Hypertrophy vs muscle gain

It wouldn’t be crazy to think that building muscle and strength are synonymous, although this isn’t actually the case. Naturally there will be a crossover between building muscle and strength, you will build some muscle when strength training and develop strength when training for hypertrophy (muscle gain). However, you won’t be able to build serious muscle when strength training or strength when hypertrophy training. In this section I will explain the difference between strength and hypertrophy training, plus help you to understand what’s going on a physiological and hormonal level.

Muscle gain

When muscles undergo intense resistance training trauma to muscle fibres occur. The muscles then undergo a process of repair, and or replacing damaged fibres. The damaged muscle activates satellite cells (see muscle damage).

Within hours of training white blood cells called neutrophils and macrophages (needed to decrease inflammation) saturate the injured muscle. Immune cells release a cell signalling protein called cytokines. The cytokines then attract more white blood cells and satellite cells (specific type of stem cell) to the damaged area. Satellite cells facilitate the complex processes of muscle repair. Satellite cells possess a single nucleus and regulate gene expression and are helped by fibro-adipogenic progenitors (FAP).

When a muscle becomes damaged, both satellite cells and FAP’s are activated and multiply rapidly. The FAP’s secrete trophic factors (food for the satellite cells). This stimulates the cells to replicate and differentiate (cell changing from one cell type to another) into mature cells fusing to muscle fibres, subsequently regenerating new muscle protein fibres in the damaged muscle. The FAP’s are then cleared. For satellite cells to work optimally it is essential to get good sleep, good quality protein and carbohydrates, optimal hydration, and a diet low in trans fats and sugar. The cell regeneration process takes 16 hours.

There are three training principles that are essential for optimum satellite cell activation:

Training principle one

It is essential to overload the muscle. If you lift a weight for ten reps, and could have performed another 5 then you won’t adequately stress the muscle to elicit the appropriate hormonal and physiological response. A program should be gradually progressed over time. Progressively trying to lift more weight each session to create an overload. Always try to lift to exhaustion. Time under tension is another important factor. Try to lift for 40-70 seconds depending on the exercise being performed, body type and goal, to allow a good pool of muscle fibre (fast twitch type one, two and slow twitch) activation, this helps to increase important muscle building hormones (testosterone and growth hormone). Studies have shown that slow lifting movements increase muscle gain more than simply lifting heavy weights, slowly on the negative phase with no rest at the top and bottom of the movement. Lifting heavy is obviously needed to produce an overload but not necessarily super heavy, this is muscle gain training not strength training.

Training principle two

For satellite cells to be activated muscle trauma/damage has to occur. As already mentioned this triggers the immune response needed for satellite cell activation. You may feel sore for a day or two after training. This is ok but not essential for muscle gain. A buildup of hydrogen ions causes muscle soreness and not lactic acid as is commonly thought. Lactic acid causes the burning sensation during training, and prevents further muscle contractions as a result of the body being unable to deliver oxygen fast enough to the muscle when training for short intense periods. In the presence of oxygen (aerobic respiration) the body shuttles pyruvate (that can be made from glucose) into the krebs-cycle to be broken down for energy. In the absence of oxygen (anaerobic respiration), with intense training for example, lactate dehydrogenase catalyzes the pyruvate to the 3-carbon compound by-product, lactic acid

(fermentation). As lactic accumulates it blocks the transport of fatty acids into the mitochondria to be oxidized for energy. This is fine when resistance training (as the lactic acid stimulates an important muscle building hormone response), but when performing high intensity cardio, (which results in the release of fatty acids into the bloodstream) the fatty acids cannot be utilized. This doesn’t mean you shouldn’t do high intensity cardio - this is covered in the HITT and fat loss section. Lactic acid production is the body’s way of preventing muscle injury. This lactic acid is then transported back to the liver and converted back to pyruvate and then glucose (gluconeogenesis).

Training principle three

Metabolic stress causes cell swelling (the pump) around muscles, which contributes to muscle growth without necessarily increasing the size of the muscle cells. The swell, which comes from the addition of glycogen into the muscle, is known as sarcoplasmic hypertrophy. This gives the appearance of larger muscles without necessarily a significant increase in strength. It is this that is the primary difference between muscle gain and strength training.

Sarcoplasmic hypertrophy is an increase on diameter without an increase in muscle fibre density. Sarcomere hypertrophy is an increase in muscle fibre density, without an increase in the diameter, strength training.

The body breaks down and rebuilds muscle every two weeks to one month and weight lifting speeds this process up. Rebuilding peaks 24 to 36 hours after training, and can continue for as long as 72 hours. This shows that same muscles can be worked more than once a week. In fact, it is thought to more beneficial to train a muscle as much as three times a week, although this does depend on body type. Different body types seem to have a quicker recovery rate from other body types, which is reflected in the YBP training programs.

As mentioned already, for effective muscle growth it is essential to initiate the correct hormonal response. Lifting weights creates a stress, and to counteract that stress, hormones are released.

Training intensity should be your number one priority to enlist the greatest number of satellite cells and kick off the muscle-growing process.

Insulin-like growth factor 1 (IGF-1)

Related to insulin and highly anabolic, IGF-1 is a key regulator of muscle growth. It is thought that it contributes to muscle growth by stimulating the proliferation of satellite cells. It regulates the amount of muscle growth by enhancing protein synthesis, facilitating glucose uptake and repartitioning amino acids into skeletal muscle.

Things that have been shown to increase IGF-1 are:

  • To train short and intensely

  • Eat good fats (the percentage depends on body type)

  • Supplement creatine*

  • Consume whey protein before and after workouts

  • Eat meat (carnivores have been shown to have higher IGF-1 than vegans)

  • Drink milk *

  • Supplement vitamin D

* It is true that studies say that both creatine and milk increase IGF-1, but personally I try and avoid both due to their associated side effects.


Insulin is a protein and it is produced and released by the pancreas. Insulin is released after you eat carbohydrates and/or protein. Like other proteins insulin is a chain of amino acids. Insulin has a folded structure like human growth hormone, which makes it act more like a signalling hormone rather than a building block.

Insulin enters the bloodstream from the pancreas and travels to body tissues, including muscle tissue. The muscle fibres (or cells) are lined with insulin receptors. When the insulin molecule attaches to the receptor, it activates the muscle cell to open and allow glucose, amino acids, and creatine to enter the muscle cells. This is one reason insulin is so important for muscle growth. When insulin attaches to the muscle cells, it initiates biochemical reactions in the muscle that increase protein synthesis and decreases muscle breakdown, which further enhances muscle growth. Insulin also increases blood flow, helping to get more nutrients like glucose and amino acids to the muscles. Bodybuilders consume simple carbohydrates on contest day creating a spike in insulin, which pushes the carbohydrates into the muscles, making them full (bearing in mind that they have become very insulin sensitive after being on a very low carbohydrate diet leading up to the competition). By encouraging our blood vessels to relax and dilate insulin also increases blood and nutrient flow to aid the healing process from training induced muscle damage. This is one reason post exercise carbohydrate intake is so important regardless of specific goal. Insulin increases how much muscle glycogen is stored in muscle tissue.

Insulin enhances satellite cell fusion. It does this by increasing satellite cell density, promoting extensive myotubular formation (developing muscle fibres) and enhances differentiation.

To maximize insulin's effects you should eat fast-digesting carbohydrates after training (the amount depends on weight, body type and goal), supplementing alpha lipoic acid (ALA) (an antioxidant that mimics the effect insulin has on muscle cells which may enhance insulin sensitivity). Insulin sensitivity creates the best environment to provide energy to power satellite cells.


Testosterone is an androgen (a steroid that stimulates or controls the development and maintenance of male characteristics) that is essential for satellite cell activation. Testosterone increases neurotransmitter levels (chemical messenger that carries, boosts, and modulates signals between neurons and other cells in the body) at the muscle fibre site, stimulates growth hormone (GH) responses in the anterior pituitary, interacts with nuclear receptors in DNA, and modulates satellite cell activity through increased IGF-1 production and androgen receptor (found on the surface of cells) density therefore optimizing satellite cell proliferation and differentiation.

To increase testosterone production you should:

  • Reduce or eliminate alcohol, caffeine, cigarettes, and other such drugs, as these increase cortisol, which may reduce testosterone production and also increase fat storage.

  • Time your carbohydrate intake correctly. It’s important to eat high glycemic carbohydrates at the right time. Over consumption of the wrong carbs at the wrong time can reduce testosterone immediately.

  • Get good uninterrupted sleep, as it is thought to increase testosterone levels (aim for at least eight hours a night).

  • Maintain a body fat level below 12 percent for males and 20 percent for females. This is ideal to balance your hormone levels and prevent decreasing your testosterone levels.

  • Eat healthy fats such as avocados, olive oil, fatty fish, nuts, and lean animal meats, as they are needed for testosterone production.

Intense training sessions with multi-joint movements (between 40 to 60 minutes depending on body type) help to maximize testosterone production. Most testosterone (98%) is bound to sex hormone binding globulin (SHBG) and a protein called albumin, training appears to increase testosterone availability by increasing free testosterone and making muscle cell receptors more sensitive to testosterone's effects.

Growth Hormone

Growth hormone (GH) stimulates the production of IGF-1. Secreted from the anterior pituitary gland following intensive weight sessions, GH is essential for the uptake and final-stage integration of amino acids into new muscle proteins.

GH controls how large our muscle fibres grow and is also thought to promote the second phase of myogenesis (formation of muscular tissue).

To increase GH you should:

  • Train hard, quick-bursts of HIIT (high intensity interval training), 30 seconds, five times, above lactic threshold appear to enhance GH production. This activates fast-twitch muscle fibres, which in turn, maximizes GH levels.

  • Sleep also boosts GH production. The first hour of sleep produces the strongest wave and then there are episodic waves every 90 minutes.

  • Supplement with arginine and lysine immediately before training and sleeping.

  • Glutamine supplementation after workouts and before bed will improve your immune and digestive system integrity and muscle recovery, but also elevate GH levels.


Cortisol has a bad reputation, but in fact it is an essential hormone needed for good health. Cortisol is still important for the regulation of inflammatory responses in the body and the balancing of blood sugar in times of stress. It is also an essential anti-stress hormone. If you didn’t have cortisol you would go into shock after trauma and probably die. Post exercise cortisol helps supply fat to the muscle to help power muscle protein synthesis.

Cortisol is released by the adrenal cortex above the kidneys in response to low blood sugar. In a fasted state adrenaline is released and subsequently cortisol, which stimulates gluconeogenesis (formation of glucose from non-carbon sources, such as amino acids and glycerol) and initiates anti-stress and anti-inflammatory pathways. Cortisol along with glucagon, is needed to obtain glucose for energy from stored glycogen, this process is called glycogenolysis. For glycogenolysis to occur an enzyme called glycogen phosphorylase cleaves a molecule of glucose from the long chain of glucose molecules (glycogen) and adds a phosphoryl group, producing glucose-1-phosphate. For this to be able to leave the cell and be utilized for energy it is converted by the action of an enzyme called phosphoglucomutase to glucose-6-phosphate.

Cortisol is released by the adrenal glands under conditions of high stress (mental and/or physical and even high temperature) and is the body's primary catabolic hormone. Its functions include the reduction of protein synthesis, the conversion of protein to glucose (gluconeogenesis) and the inhibition of tissue growth. This is why cortisol is associated with muscle breakdown (proteolysis).

So why if cortisol is a catabolic hormone that promotes the breakdown of carbohydrates, proteins and fat is it associated with fat storage, especially around the middle?

One thought is that the chronic release of cortisol (when you are in a stressed state), and therefore the increased chronic breakdown of essential fuel compels the body to up-regulate fat receptors on cell membranes. When in a stressed state cortisol is released, subsequently causing the body to release stored fuel. If you were stressed because you were running from a lion for example, then this extra fuel would be perfectly necessary, but generally increased cortisol levels are caused by mental stress, from work or maybe a relationship for example. There are two things happening, the glucose, which is obtained from stored carbohydrates, fat and protein is now floating around in your blood stream, to fuel a non-existent fight or flight situation. The unused abundance of fuel, now at dangerous levels, needs to be removed from the bloodstream and re-stored as soon as possible. Although it may have originally been acquired from protein or carbohydrate sources, some will be re-stored as fat. The second thing is that the chronic release of cortisol, and subsequently chronic fuel breakdown, sends the body into a panic that it will soon run out of essential stored energy, so it up-regulates fat receptors on cells increasing its fat storing capacity and therefore fat storage

Cortisol is a steroid hormone that has catabolic effects opposing testosterone, growth hormone and insulin. Excess cortisol reduces human growth hormone and testosterone output, contributes to osteoporosis, reduces muscle, slows metabolism and increases abdominal fat, impairs memory and learning, reduces glucose utilisation and suppresses immunity.

Cortisol is also released first thing in the morning. Exercising on an empty stomach first thing in the morning has been shown to actually intensify cortisol's effects thus resulting in a slowing of metabolic rate. Although in some cases certain body types with specific goals may find exercising in a fasted state beneficial this is not the case for all body types.

All exercise will create cortisol release. People who train in endurance type events like marathon training will produce a lot of cortisol. Well-trained experienced people produce less cortisol. High intensity training, like a resistance workout or interval training when rest periods are short and intensity is high, creates a rise in plasma cortisol concentrations. This is why training low intensity for hours in order to lose fat does not work. The correct lifestyle and dietary protocols will help keep cortisol levels under control.

The time of day you train also has an effect on cortisol. Training when cortisol is already high (in the morning) doesn’t cause it to rise above already elevated levels, so as it is already high training in the morning prevents a secondary cortisol peak.

As we know, cortisol has a catabolic effect on our muscle (mainly fast twitch) and bone, but it is important to remember that the acute increase in cortisol following exercise is necessary to stimulate the inflammatory response needed for the repairing and remodelling of muscle. It is long-term chronic cortisol release caused by stress that has the catabolic effect. See our stress section for more information.

Other factors that affect muscle gain

Certain body types will naturally find it easier to grow muscle than others. Age and gender will also determine the amount of muscle a person can grow. The older you become the harder it is to build muscle. Ageing mediates cellular changes in muscle, decreasing actual muscle mass. This is called sarcopenia. Weight training has been shown to slow down and in some cases even reverse this muscle loss. Resistance training also prevents injury in the elderly by improving the strength and integrity of connective tissue.

Woman will find it harder than men to increase muscle as they have much lower levels of the important muscle building hormone, testosterone.

Weight training is important for women, don’t be afraid of muscle - read more about this in our article men and women are not the same.

Your natural genetic body type has a massive say in the amount of muscle you are able to grow. There are 3 main body types (somatotypes), which are ectomorphic, mesomorphic and endomorphic.

It is possible that you may fall between one of two categories. For example, someone who falls between an ectomorph and mesomorph we classify as an ecto-mesomorph and someone between a mesomorph and an endomorph is classified as a meso-endomorph. The more ectomorphic your body type the harder it is to build muscle, and the training and dietary strategy needs to be different from other body types.

Strength training

It’s a common misconception to assume that a big muscle equals a strong muscle. Being able to activate as many muscle fibres as possible is essential to maximise strength. The central nervous system controls how many fibres will be activated for any given movement, this is to prevent injury. You will never activate 100% of your muscle fibres even when lifting your one rep max.

Motor neurons

Increasing the quantity of muscle fibres you can activate will help you to lift more and increase strength. The activation of these muscle fibres is carried out by the central nervous system. When you lift a weight a message is given for your muscle to contract from the brain down the spinal cord to the nerves attached to your muscles called motor neurons. These motor neurons initiate muscle contraction. Each motor neuron controls the contraction of a specific group of muscle fibres. The more motor neurons that are activated, the greater the number of muscle fibres that will contract. Training with heavy weights at the 2 to 6 rep range will create the necessary adaptation to increase the number of motor neurons. Motor neurons send electrical impulses to muscles. The frequency of these electrical impulses varies; a low frequency causes a sluggish muscle contraction and a high frequency a fast powerful one. Plyometrics play an important role in increasing the power of nerve impulses.

Size of the muscle

There is a correlation between the size of muscle fibres and the strength they are capable of developing. The stronger a section of muscle fibres attached to a motor neuron the more force will be generated by a nerve impulse.

Intramuscular coordination

When an untrained individual performs a movement they do so in a disorderly fashion. This is because the motor neurons discharge their electrical impulses in an irregular manner. The muscle fibres contract in a random and therefore ineffective and disorganised way. Regular training helps the muscle contraction to happen in a coordinated manner.

You may notice how on some days you are stronger than on other days. This is due to the efficiency of the central nervous system. A well-rested central nervous system will reveal its efficiency and you will be strong. Conversely if the central nervous system has not fully recovered the weight you lift will seem heavier than it actually is.

When strength training we use different energy pathways depending on the type, intensity and duration of exercise, the body uses a lot of energy. Performing lower repetitions (2 to 6) for 5 to 15 seconds the energy source used comes from the Adenosine Triphosphate Phosphocreatine system. The ATP-PC system uses phosphates to produce energy very quickly without the use of oxygen. There are very small amounts of stored ATP in the muscle, which can only provide enough energy for a short but powerful movement. The body then needs enough rest (2.45 to 4 minutes) to sufficiently resynthesise ATP.

Studies have show time and again that you will lift more weight and therefore become stronger with the correct rest period, specific to ability level and body type. For example, more rest is needed for an ectomorph compared to an endomorph and a beginner versus an advanced trainer.

Good fats are important in the diet for strength training, not just for the hormone production and boosting benefits, but also for neuron performance. Most of the axons in the central nervous system are wrapped in myelin, a substance rich in lipids (fatty substances) and proteins. Myelin insulates and protects the axon and helps speed up nerve impulses, much like the coating found around an electrical wire.

Energy systems

Depending on the sport, duration and intensity of an activity the body will utilise different fuels and energy systems. There are three main systems.

The term aerobic simply means with or using oxygen, the opposite, without or not using oxygen, is called anaerobic. ATP (Adenosine triphosphate) is the body’s energy currency. ATP cannot be stored in the body so needs to be generated very quickly. Although ATP can be generated anaerobically, although only in small quantities, a lot of ATP can be made in the presence of oxygen, allowing the activity being performed to last longer. The formation of ATP is a complex one requiring several substances and enzymes, producing different by-products depending on the energy system being utilised.

The aerobic and anaerobic energy systems do not work individually, but overlap, although one will be working more than the other. It’s the intensity and duration of a specific activity that determines which energy system will be utilised.

ATP-CP system

The first system is the anaerobic or adenosine triphosphate- creatine phosphate system (ATP-CP). This system solely relies on stored ATP in the muscle and that muscle's capacity to regenerate ATP from a finite amount of phosphocreatine (PC). These two substrates will rapidly deplete without oxygen so too will the activity being performed. This system is used with short duration high intensity activities that last less than ten seconds. The fuel used in the specific system is creatine phosphate. Events/sports people like shot putters, weight lifters, American football linemen, 100m sprinters and speed skaters will use this system. The waste products from this system are minimal as the duration is so short. This is the system and fuel utilised during strength training.

You will find when pushing your body this hard that after 15 to 20 seconds the pace will inevitably slow. Lactic acid within the muscle will increase, slowing the ability of the muscle to contract. At this point you will either have to stop or lower the intensity, subsequently moving into a different energy system.

This is a good system to boost athletic performance.

Glycolysis system

The second system is called the anaerobic lactic (AL) system (also known as fast glycolysis). This system utilises glucose obtained from muscle where it is stored as glycogen. It is this system that takes over from the ATP-CP system, generating power for longer. It provides energy for medium to high intensity bursts of activity that last from ten seconds to two minutes. Activities like football, rugby, sprinting, American football skill position, middle distance runners (400m-800m) would use this system. This system, as with the ATP-CP system, works at the higher intensity end of the scale and does not require oxygen for fuel to produce energy. The difference between the two is that a person can work at a longer duration with the anaerobic lactic system, albeit at a slightly lower intensity. As a result, waste products such as lactic acid accumulate in the blood and in muscle cells causing a burning sensation in the muscle. It is at this point of being in an anaerobic system that shortness of breath and fatigue will inevitably set in. Training with explosive short bursts like this for 30 minutes will burn a lot of calories. At the high intensity phase the main fuel will come from glucose. During the low intensity recovery period between exercises fat will also be burnt. During the high intensity phase fatty acids will be released into the blood, however the circulating lactic acid blocks their uptake into the cell mitochondria (the powerhouse in the cell where fuel is burnt to produce energy). As the intensity drops, so too will the lactic acid levels and the utilisation of fat will increase. Training in this way will give a metabolism boosting effect. This is called EPOC (excess post-exercise oxygen consumption). It is believed that training in this way will increase the metabolic rate by 15% over the following 24-hour period, increasing fat burning. (It is when your body is at the lowest intensities that the highest percentage of fat is utilised). When you train in this system on a regular basis you become more efficient at burning calories and generating energy, as this type of training increases the number of mitochondria (organelle in which fuel is oxidised and energy is produced) in muscle. This will in turn maximise the ability of the muscle to burn carbohydrates and fatty acids for ATP. Exercise creates a low-energy signal known as AMP (Adenosine monophosphate, synthesised from ATP). When there is a rise in AMP, the body will up-regulate ATP production to prevent an energy deficit. Muscle contraction whilst training produces a 300 to 10,000% increase in intracellular calcium increasing contractile ability. The rise in both AMP and calcium are strong signals for the production of new mitochondria, which occurs in the resting state immediately following exercise.

There will also be an increase in testosterone and growth hormone immediately post exercise, which will have an anabolic (growth) affect. The more muscle you can build, the faster your metabolism will become, creating a good fat burning environment while at rest. For women worried about building muscle, please read the article on why women will struggle to build muscle.

Aerobic system

The third system, which can be broken into two parts, is the aerobic system. This system needs oxygen and can produce more ATP than the previous two. This system uses the heart, lungs and circulatory system to provide the muscles with the necessary oxygen to produce energy. This system starts to be engaged after about 30 seconds and lasts up to 2 hours, utilising both stored glucose (glycogen) and fat. After about two hours the stored glycogen will be depleted (this does of course vary from person to person) and fat becomes the main substrate used for fuel. Carbon dioxide and water are the waste products produced and are expelled allowing the activity to continue. The aerobic system is the most utilised of the three. It provides energy for low intensity activities. Activities such as long distance running, long distance swimming, crew (rowing) and sea kayaking rely on the aerobic system.

The science of fat loss

The body regards fat as wealth, like money in the bank. The body is wired to store fat easily to guarantee it has energy to live in times of famine. Fat is also the main source of fuel between meals, while resting, sleeping and during low intensity activities. Fat obviously gets a negative press, when in fact it is essential for health. Fats regulate and manufacture hormones, transport vitamins and minerals throughout the body, store essential minerals (A,D,E and K), are essential for structural integrity of cell membranes and are the largest source of energy in the body.

It was once thought that a low-fat diet would be the answer to the growing obesity epidemic spreading across the western world. We now know that certain fats are beneficial, not only for health, but also fat loss. Next it was carbohydrate that was to blame, with the emergence of high protein, low carbohydrate diets, again not necessarily the answer. The point here is that the over consumption of any food group will lead to fat storage. At YBP we believe that everyone is different, some people would benefit from eating more carbohydrates, while others would do well on a higher fat diet, but everyone needs both, just at different times, and in different quantities. Carbohydrates are not bad, fat is not bad, they just need to be used correctly.

There is a lot more to fat loss than meets the eye. It’s a crude approach to assume that eating less calories and exercising more is always the answer. The approach needs to be tailored to the individual. Many factors can affect a person’s weight and the ability to lose fat.

Weight gain is not always as simple as a lack of activity and eating too much, there are many factors that should be taken into consideration.

Genetics - some people are genetically programmed to burn energy at a lower rate. An endomorphic body type tends to have a slower metabolism than an ectomorph.

Incorrect food choices – some people may be making the wrong food choices without realising. These choices may be learnt in childhood, come from cultural influences, or perhaps the socio-economic group, and can lead to eating food that will, for different reasons, cause fat gain. Some people may just be eating the wrong food at the wrong time of day for their body type, even if they are consuming what are considered to be healthy foods.

Diabetes - diabetics struggle to control their weight as excess glucose in the blood is converted to fat (please read the diabetic guide for more information).

Pathophysiology - low levels of leptin, the hormone that controls appetite, can cause an individual to overeat, as can low levels of serotonin. (See hormones and fat loss guide)

Blood sugar imbalances - high sugar consumption, stress and stimulants (such as tea and coffee) will contribute to an imbalance in blood sugar, and the subsequent hormone imbalance that accompanies it. Excess sugar in the blood will be stored as fat and can result in sugar cravings and adrenal stress, which in turn can suppress thyroid function. (See blood sugar balance guide)

Allergies or food intolerances - food allergies tend to produce an immediate and severe response, but many people suffer from intolerances to foods they consume frequently, unaware that many of the minor symptoms they are experiencing are due to foods they are eating. Wheat and dairy are among the most common culprits. (See our allergy and intolerance guide for more information or if you suspect you have either an allergy or intolerance).

Underactive thyroid - the thyroid gland helps to control metabolism and subsequently greatly effects weight. Low thyroid function can be borderline and thus not picked up on routine blood tests. (See our thyroid guide).

Dehydration - many people do not drink enough water, leaving them dehydrated. Water is essential to help eliminate toxins and dilute sugar or protein in the blood. Toxins are released when fat stores are broken down. Toxins damage and disrupt body cells, so they are stored in fat to nullify and reduce potential damage. (Please read our liver guide).

Digestive problems - digestion is fundamental to the way our body absorbs, simulates and stores food. Digestive problems are frequently implicated with weight issues. Potential problems include low stomach acid, low digestive enzymes and yeast overgrowth such as Candida, parasites and bacterial infections. (See our digestion guide for more on this).

Nutrient deficiencies – a wide range of nutrients are required to support metabolic processes. Essential fats are particularly important, B vitamins, vitamin C, zinc, choline, inositol, chromium and manganese are especially useful for weight control and metabolism.

Toxicity and poor liver function - the liver is the central organ of detoxification and also plays a key role in the digestive process. It is involved in blood sugar balance and the recycling of excess hormones such as oestrogen (which can contribute to weight gain), and toxic removal. (See liver guide).

Hormones - many hormones are involved in fat burning (lipolysis) such as glucagon, adrenaline, insulin, cortisol, thyroid hormone, testosterone, leptin, ghrelin, human growth hormone, oestrogen, progesterone and DHEA. Some need to be high, while others low, to elicit the correct fat burning affect. Oestrogen is a fat storage hormone and contributes to weight gain. Oestrogen dominance (in relation to progesterone) can affect thyroid function by inhibiting its ability to produce thyroid hormones, contributing to hypothyroidism. Weight gain may occur pre-menstrual and at the menopause. Hormones are also involved in appetite control.

Psychological factors - stress and depression are often triggers for comfort eating, but they also have a physiological effect on your body. Stress is a massive trigger for fat gain and also a huge obstacle in the way of fat loss. (See stress guide for more information)

Environmental and lifestyles factors – these include fast food consumption, recreational drugs, medication, lack of sleep, sedentary lifestyle, stimulants, smoking and alcohol. Alcohol has many negative effects when trying to lose fat. (Please see alcohol and caffeine guides for more)

Under eating - commonly when trying to lose weight the tactic is to either reduce calories and/or increase activity. This will be the right approach for the majority of people, but not everyone. If we do not eat enough calories for our specific energy needs, our body will move into starvation mode, by up-regulating the hunger hormone ghrelin and slowing metabolism. Ghrelin is secreted from the lining of the stomach when it is empty between 2 to 5 hours after a meal. It is possible to mentally override hunger signals, but this approach is both unhealthy and hard to maintain. The opposite hormone to ghrelin is leptin (protein responsible for satiety signals). Leptin is secreted from fat cells (adipocytes) into the circulatory system and (like ghrelin) travels to the brain to activate the hypothalamus. The higher number of fat cells you have the more leptin is produced. If a higher number of fat cells equals more leptin, why do overweight people struggle to lose fat? The answer is leptin resistance, which is explained in a little more detail later in this guide. A hormone called cortisol is also released when you under eat. Cortisol has the effect of slowing metabolism and subsequently increasing fat storage. Another appetite suppressing hormone is serotonin. Serotonin is converted from the amino acid tryptophan aided by B vitamins. Serotonin is also a powerful mood regulator, making you feel less anxious, more relaxed and also more energetic and focused. Serotonin is made after eating sweet or starchy carbohydrates. If tryptophan is an amino acid, which means it comes from protein, why is serotonin synthesised after eating carbohydrates? Amino acids compete with one another for absorption. When we eat sweet or starchy carbohydrates they are broken down into glucose in the intestinal tract and released into the bloodstream. The presence of sugar in the blood initiates the release of insulin from the beta cells found in the islets of Langerhans in the pancreas. The hormone insulin pushes the sugar and amino acids into the cells, to be used for energy or stored. Tryptophan tends to get left behind in the blood while other amino acids get absorbed. The insulin surge pushes the left behind tryptophan across the blood brain barrier into the brain, increasing serotonin production. B vitamins found in whole grains and legumes help the body convert the hormone tryptophan into serotonin. Tryptophan-rich foods include turkey, salmon, tuna and dairy products. Outside of diet, regular exposure to direct sunlight also stimulates serotonin production.

What is body fat?

Body fat is stored in white adipose tissue under the skin. Contrary to outdated beliefs, new fat cells can be produced at anytime of life and we don’t have a set number. Fat is stored inside cells called adipocytes in the form of triglycerides (three fatty acids attached to a glycerol backbone).

There are three types of fat. Firstly there’s the fat that is stored for fuel in adipose tissue beneath the skin and is biologically active. The second is known as essential fat, which is found in the central nervous system, bone marrow and muscle. In men essential fat constitutes 3% of total body fat and 12% in women. Women have a higher percentage of fat, as it is essential for reproduction, this is stored in breasts, pelvis, hips and thighs. The third fat is visceral fat, which is found around the organs. Too much visceral fat is linked with an array of health problems.

Fat stored around the abdomen is related to a greater risk of disease than fat stored on the thighs, bum, hips and upper arms. Fat around the abdomen releases fatty acids, inflammatory compounds, hormones (that lead to increased blood fats), blood glucose, increase blood pressure, and aromatase. Aromatase is the enzyme that converts testosterone to oestrogen (a fat storage hormone). Fat around the abdomen is related to high, chronic cortisol levels, caused by stress (stress comes in many forms, physical and psychological). Ironically cortisol is a catabolic (breakdown) hormone. When levels are chronically high the body overreacts to the potential catabolic effects by up-regulating fat storage mechanisms subsequently increasing fat synthesis.

Adipocytes are metabolically active and regulate their number and size by secreting signals, such as the hormone leptin. Leptin gives the signal of satiety, switching off hunger signals. The more fat a person has, the more pro-oxidant, harmful cytokines, such as c-reactive proteins, are also secreted. The leptin binds to these pro-oxidants and cannot pass through the blood-brain-barrier to signal the brain to stop eating, leaving the secreted leptin ineffective. Leptin then builds up in the blood unable to get to its destination and bind to the necessary receptors. The increase of leptin in the blood produces a down regulation of leptin output, assuming there is enough, inevitably leading to leptin resistance.

Eating a diet high in processed foods, sugar (especially fructose), and grains (in excess) can contribute to leptin-resistance. Sugar also causes inflammation and the production of inflammatory cytokines.

Eating at the correct times is essential for hormonal balance, depending on your body type and goal. Some body types are better eating more regularly, while others are better leaving gaps between meals. Those with a faster metabolism (ectomorphs) have a smaller storage capacity and will naturally use their liver energy stores (glycogen) faster than other body types, so we recommend eating smaller and more regularly to keep those stores replenished. Body types with a slower metabolism (endomorphs) have a larger energy storage capacity and should eat less frequently to allow the use of stored energy. It is important for an ectomorph not to completely deplete their liver glycogen stores, as this will create a catabolic (breakdown) environment, increasing the chances of muscle breakdown. Conversely, the more endomorphic body types tend to carry more muscle, so it is not a concern if they move into a catabolic state between meals, depending on the specific goal. For the more endomorph body type the bigger gaps between meals allows insulin levels to fall, which is beneficial for fat loss. After eating insulin levels rise, while there is insulin in your blood stream the fat burning mechanisms are inhibited and fat storage increases. There are a lot of sources recommending we should eat small and regular meals, this will work for some but not everyone.

Drinking water between meals is always a good option to keep hunger at bay.


Metabolism is another important factor in weight management. Metabolism is the chemical process that occurs within a living cell or organism that is necessary for the maintenance of life. Within metabolism substances are constantly broken down (catabolism) for energy and synthesised (anabolism) to replenish and repair. Everyone’s metabolism runs at a different rate. You will ordinarily find that an ectomorph body type has a faster metabolism, while an endomorph body type is slower.

Many factors affect metabolism. Not eating the correct number of calories per day will slow metabolism, in an effort to conserve energy and prevent the body slipping into starvation mode. The number of meals varies for different body types and goals. A common mistake is to reduce calories too far in an effort to burn fat. This is why fad diets rarely work in the long term. Crash dieting generally results in some initial “weight” loss, coming from stored carbohydrate (glycogen) and water, not fat. Also extreme diets are commonly low in essential nutrients that are critical for every system in the body to work efficiently. Long term crash dieting will inevitably lead to muscle loss, slowing metabolism and subsequently increase fat storage.

  • Movement, exercise and activities will increase metabolism. Take the stairs, walk or ride a bike instead of driving for example.

  • Studies have shown that increasing your water intake can speed up metabolism by 40%. It is not known how this works, but one theory is that the metabolic increase occurs when the body attempts to heat the ingested water to core temperature.

  • Coffee contains caffeine, which is a stimulant. Stimulants will boost metabolism. However, be aware that there are side effects to drinking too much caffeine, such as, insomnia, headaches, stomach upsets, dizziness and more. Green tea is a good alternative.

  • Metabolic rate decreases by 5% a decade. This is partly due to loss of muscle tissue as we age. Men generally burn calories at a faster rate than women because they have a higher muscle mass.

  • Thyroid disorders can either speed up (over active) or slow down (under active) metabolism. Low carbohydrate diets have been shown to slow thyroxine output subsequently contributing to slowing metabolism. Studies have shown that eating less carbohydrate will help with fat loss, however the reduction amount should be tailored for the individual. Cutting carbohydrate too far will slow thyroid hormone (thyroxine) output, which will in turn slow metabolism. The type of carbohydrate that is eaten is also important. Studies show that there is more weight gain (in the form of fat) from eating high glycemic carbs versus low glycemic carbs, and over eating carbs at one sitting is not advisable. The body only has a finite capacity to store and process carbohydrates at one time. Other hormonal disorders such as PCOS will also slow metabolism.

  • Body composition is also an important factor (the ratio of muscle to fat). Muscle is denser and more metabolically active than fat, requiring more energy and increasing metabolic rate.

  • Living in tropical climates has a 5 to 20% increase in base metabolic rate. It takes more energy to keep core temperature down. Exercising in a higher temperature will also have an additional boosting affect.

  • Strength training builds muscle density. Muscle burns 73 calories more than fat per kg per day. Combined with the correct type and frequency of cardio training, a resistance routine is essential for any fat loss programme. Studies have shown that cardio exercise has a beneficial influence on increasing metabolism. Cardio, but especially high intensity cardio, increases both mitochondria (powerhouses within the cell, that burn fuel for energy) and the compound cytochrome c (needed for aerobic energy production in the electron transport chain). There is more in depth information about this later in this guide.

  • Spices have been shown to have a little effect on increasing metabolism.

The fat journey

The process of fat digestion begins in the mouth with the mechanical grinding of the teeth to break down the fat into smaller pieces. Enzymes called lingual lipases in the mouth start to emulsify the fat and the saliva makes it moist and easier to swallow. Once in the stomach the fat is further broken down by gastric lipases into a semi-liquid state known as chyme. This now passes through into the duodenum (upper small intestines), which is where most fat digestion takes place and also were most nutrients are absorbed. Hormones signal the gallbladder to contract pushing bile into the small intestine. Fat is hydrophobic, which means they do not dissolve in water. When the fat enters the aqueous intestinal environment, bile is required to emulsify the two substances. One end of the bile molecule is a hydrophobic (water fearing) and the other end is hydrophilic (water loving). The hydrophobic end attaches to the fat molecule, while the hydrophilic end protrudes out attaching to the water, the fat and water don’t actually touch. Once the two are combined they are called micelles and provide a larger surface area in which the lipases can work. Enzymes work better in an alkaline environment, however the chyme is acidic after leaving the hydrochloric acidic environment of the stomach. Bile produced by the liver and stored in the gallbladder is secreted along with bicarbonate ions, which neutralise the acidic pH of the chyme.

The different lipases work at different sections of the digestive process, and in different PH environments. The first is lingual lipase, which is secreted from glands under the tongue, gastric lipase (stomach) and pancreatic lipase (pancreas). The lipases break down the micelles, which contain fat in the form of triglycerides. Triglycerides (3 fatty acids connected to a glycerol backbone) are broken down onto a mixture of diglycerides (2 fatty acids) and monoglycerides (1 fatty acid) and free fatty acids. The intestinal mucosal cells absorb monoglycerides and diglycerides, this allows them to pass through the wall of the small intestines, before being built back into triglycerides. In the enterocytes (cells lining the intestinal wall) the triglycerides combine with cholesterol, phospholipids and protein forming structures known as lipoproteins. The lipoproteins are solubilised (making them soluble in water) by a coating of protein allowing them to travel through the aqueous lymph vessels and subsequently into the bloodstream. Lipoproteins are classified by their differing degrees of density. Lipid is less dense than protein. The lower the density, the less protein. Collectively they are called chylomicrons. These chylomicrons are then released into the bloodstream via the lymphatic system, were they are either stored, or oxidised for energy. Some triglycerides are synthesized in the liver, packaged into VLDL’s (very low-density lipoproteins) and released directly into the bloodstream.

The triglycerides contained within the chylomicrons need to enter the cell to be either used for energy or stored (catabolised or synthesised respectively). This transportation process is catalysed by two enzymes called LPL (lipoprotein lipase) and HTGL (hepatic triglyceride lipase). These enzymes hydrolyse (chemical reaction involving water) triglycerides from the chylomicrons and VLDL’s into free fatty acids and glycerol. This process happens in the capillaries of tissue, such as adrenal glands, liver, skeletal muscle and adipose tissue so the free fatty acids can be absorbed into cells for energy or storage, the glycerol is transported to the liver and kidneys via the bloodstream. The concentration of LPL depends on the body’s nutritional state at the time. Fat can come from a recently ingested meal, that has entered the blood from the lymphatic system, in the form of chylomicrons, found in adipose cells, attached to albumin in the bloodstream or in the liver where it has been synthesised from excess glucose and packaged as VLDL’s

In the fed state after a meal (postprandial), high glucose levels stimulate the release of insulin from the pancreas facilitating glucose uptake into the cells.

An interesting point is that high levels of insulin stimulate the release of LPL from adipose cells facilitating the uptake of free fatty acids and monoglycerides into the cells for conversion back into triglycerides for storage, this is known as fatty acid synthesis.

While insulin stimulates adipose cells to secrete LPL it simultaneously inhibits skeletal muscle LPL secretion, preventing fatty acids being taken up by muscle cells and used for energy.

As already mentioned, in the fed state when insulin is high and glucagon low, our cells take up glucose, and we are in an anabolic state. If we have a sedentary lifestyle and do not need this glucose for energy it will be stored as glycogen, when our glycogen stores are full the excess glucose needs to be converted and stored as fat. This is called fatty acid synthesis (lipogenesis), where triglycerides are formed from glucose. (Read in more detail Fatty acid synthesis in the coming section)

Fatty acid synthesis

When blood glucose levels are high (fed state) fatty acid synthesis will occur in the liver. The specific hormone that regulates this state is insulin. When there is a lot of ATP being produced there will be a natural proclivity to store fuel. When glucose enters the cell using a specific transporter it gets converted to pyruvate, then pushed into mitochondrial matrix and converted to acetyl CoA a 2-carbon molecule. This is our precursor for fatty acid synthesis, converting a monomer (acetyl CoA) to a polymer (fatty acid chain). The first obstacle that needs to be addressed is that the enzymes required for lipogenesis are located in the cytoplasm outside of the mitochondria, while the acetyl CoA is inside the mitochondrial matrix and there are no transport mechanisms to transport either the enzymes or acetyl CoA across the mitochondrial membrane. There is however a protein shuttle that can transport the molecule citrate across the membrane into the cytoplasm where the enzymes are located. Citrate is a combination of oxaloacetate and acetyl CoA and there is an enzyme (citrate synthase) in the cytoplasm that can separate them releasing the acetyl CoA. The oxaloacetate is then recycled back into pyruvate in which a molecule of NADPH is produced. NADPH will later be used to power a reduction reaction in the synthesis of fatty acids. For any anabolic reaction energy in the form of ATP is required. Converting the 2-carbon acetyl CoA to a 16-carbon polymer (palmitic acid) would require 14 NADPH and 8 ATP molecules. The by-products of these reactions are 14 NADP+, 7 ADP, 6 H20 and 8 CoA molecules that are removed in order for the carbon molecules in the fatty acid chain to form a double bond.

The 2-carbon Acetyl CoA and the 2-carbon malonyl CoA are hydrolysed by the enzyme acetyl CoA carboxylase, adding a carbonyl group, removing Co2 (carbon dioxide) and H2o (water). This first step uses 1 ATP and 1 NADPH molecule. Acetyl CoA carboxylase is the slowest reaction in fatty acid synthesis and therefore is the rate limiting factor. The next step is the removal of the two CoA groups from acetyl CoA and malonyl CoA. This reaction is catalysed by the enzyme known as fatty acid synthase, which polymerises the 2-carbon fatty acid malonyl CoA subunits together to form a 16-carbon chain (palmitic acid). The CoA groups are removed and replaced by a carbon to carbon double bond. Longer fatty acids can be produced in this way. Three such fatty acids can now be attached to a glycerol backbone, packaged as VLDL (very low-density lipoproteins) and delivered to body tissue, for storage or to be broken down for energy.

In a fasted state (low blood glucose) glucagon is the hormone released and not insulin. Glucagon stimulates the production of LPL from skeletal muscle, increasing the free fatty acid uptake into muscle cells for energy. This is also known as a lipolytic state. When your body is in a stressed state when adrenaline is high and both skeletal and cardiac muscle are stimulated to produce and secrete LPL. This is why short intense stress can promote weight loss, however chronic stress actually causes weight gain.

Fat oxidation

Fats are stored as triglycerides predominantly in adipose tissue until needed for energy. At times in which energy is required (famine, physical activity, fasted state) stored triglycerides are broken down and transported to the tissue, generally skeletal muscle. This process is known as lipolysis. High levels of adrenalin (80%), noradrenalin (20%) released from the adrenal glands and glucagon from the alpha cells in the islets of Langerhans located in the pancreas in combination with low insulin levels stimulate fatty acid release from triglycerides in the adipose cell. These are catabolic hormones, meaning they breakdown rather than store fuel. The adrenaline and glucagon hormones dock on their respective beta-adrenergic receptors on the adipose cell wall known as g-protein coupled receptors. This then causes cAMP (Cyclic adenosine monophosphate) to be generated inside the cell. Through a series of steps this activates HSL (Hormone-sensitive lipase), adipose triglyceride lipase (ATGL) and lipase A (LIPA) in the adipose cell. HSL proceeds to cleave free fatty acids from the glycerol backbone, allowing them to be released into the blood. Fatty acids either entering the blood after digestion or released from adipose tissue stores are bound to the protein albumin for transport to peripheral tissues. Once this complex of fatty acid attached to albumin interacts with a cell surface the pair separate. The fatty acids enter the target cell cytoplasm using a protein called free fatty acid transporter, then through a series of complex reactions the process of beta oxidation begins (this process is covered in more detail here, read more).

Hormones (adrenalin, noradrenalin and glucagon) dock on their respective beta-adrenergic receptors on the adipose cells, known as g-protein coupled receptors. The binding of the hormones activates a G stimulatory protein (group of proteins known as molecular switches, found inside cells, that transmit information from outside the cell to inside) that then binds to GTP (Guanosine triphosphate). An enzyme known as AC (adenylate cyclase) embedded in the cell membrane is then activated. AC converts ATP (adenosine triphosphate) to cAMP (cyclical adenosine monophosphate). This then activates PKA (protein kinase A), which phosphorylates (adds a phosphoryl group) and in turn activates a protein called perilipin, causing CGI to separate, moving to activate the enzyme ATGL (adipose triglyceride lipase). As we know a glycerol backbone is attached to three fatty acids, the enzyme ATGL cleaves the first fatty acid, leaving a diglyceride. PKA then activates the next enzyme, HSL (hormone sensitive lipase) responsible for removing the next fatty acid leaving a monoglyceride, lastly an enzyme known as monoglyceride lipase cleaves the final fatty acid leaving the glycerol backbone (the glycerol was preventing the fatty acids leaving the cell).

The fatty acids and the glycerol backbone are then transported into the bloodstream. Glycerol is soluble and can be transported in blood on its own, the free fatty acids are not and need to be transported with a transport protein (albumin) taking them to muscle (liver heart muscles) to be oxidised to make ATP. Glycerol can also be used for energy, or by a process called gluconeogenesis (in liver), be converted to glucose. The fatty acids are now available for oxidation (burnt for fuel). The fatty acids enter the cell and need to be converted to their active form, fatty acid acyl coA. An enzyme called fatty acyl coA synthetase triggers the conversion (using energy from ATP degrading to AMP+PP) adding a coA prevents the fatty acid leaving the cell. This is known as the activation stage. The fatty acid, now called a fatty acyl coA still needs to enter the cells power house to be oxidised. The fatty acid acyl coA can only pass through structures known as porins located in the outer mitochondrial wall, entering the inter-membrane space. Another obstacle awaits the fatty acid; it is now held in the inside of the mitochondrial wall and cannot pass through the inner mitochondrial wall into the organelle. A different transport mechanism is needed to transport the fatty acid into the mitochondrial matrix, this is known as the carnitine shuttle. An enzyme called CAT1 (carnitine acetyltransferase 1) found in the outer mitochondrial wall attaches carnitine to the fatty acid releasing the coA group back into the cell cytoplasm. In the next step an enzyme called carnitine acylcarnitine translocase found in the inner mitochondrial wall transports the fatty acid acyl-carnitine into the mitochondrial matrix. This is known as the transport stage. The next problem is that acyl coA is the only form of the fatty acid that can be metabolised in the mitochondria and the coA group has been removed. An enzyme called CAT 2 (carnitine acyltransferase 2) attaches a new coA group removing the carnitine molecule which is released into the intermembrane space to be used again.

The next stage is called beta-oxidation. The name beta-oxidation comes from the specific place the fatty acid is broken down. A fatty acid is a long chain consisting of carbon and hydrogen atoms. The chain needs to be broken into portions of two carbons to be oxidised. The break of the fatty acid occurs between the alpha and beta carbons (this is why it is known as beta oxidation). Fatty acids vary in length, depending on the amount of carbon atoms they are made up of. A fatty acid made of 4 to 8 carbons is a short train, 6 to 10 carbons is a medium chain, 10 to 16 carbons a long chain and 17 to 26 is a very long chain. Short chain and medium chain are oxidized exclusively in the mitochondria, long chain fatty acids are oxidised in both the mitochondria and the peroxisomes (a cell organelle containing a large number of enzymes, including catalase and oxidase, that break down long-chain fatty acids) and the very long chain fatty acids are oxidised only in the peroxisomes.

Fatty acids consisting of 10 to 12 carbons and shorter can enter the mitochondria by diffusion (the passive movement of molecules or particles along a concentration gradient, or from a region of high concentration to a region of low concentration), long chain fatty acids need to be activated in the cell cytoplasm to be able to enter the mitochondria or the peroxisomes. The activation of the fatty acids occurs when the enzyme acyl-CoA synthase catalyzes a bond (thioester link) between the fatty acid and acyl-CoA, using energy from ATP (high energy molecule that stores energy we need). This then becomes fatty acid acyl-CoA and can be transported into the mitochondria.

The fatty acid now goes through a series of steps, oxidation, hydration, and thiolation. These reactions ultimately break down the fatty acids two carbons at a time producing acetyl coenzyme A molecules. These molecules have hydrogen atoms attached that contain electrons, which are then transported by two different electron carriers (FAD and NAD) to enter the krebs cycle (a series of enzymatic reactions in aerobic organisms involving oxidative metabolism of acetyl units and producing high-energy phosphate compounds such as ATP). Fatty acids yield high amounts of ATP (high-energy molecule that stores the energy we need to function).

ATP (adenosine triphosphate) is a molecule that carries energy to be used by cells. It is made up of a base (adenine), sugar (ribose) and a three-phosphate chain. Energy is released from ATP when one of the three phosphates is removed. When the phosphate is removed, the ATP molecule becomes ADP (adenosine diphosphate), which is a lower energy molecule. ADP can be re-synthesised to ATP using energy, or can be further degraded, removing another phosphate group becoming AMP (adenosine monophosphate).

The next step in fat breakdown is called respiration, which is the metabolic processes by which living cells break down carbohydrates, amino acids, and fats to produce energy in the form of adenosine triphosphate. Respiration can be broken down into three parts. They are called glycolysis (occurs in cell cytoplasm), Krebs cycle (occurs in the mitochondrial matrix) and the electron transport chain (occurs in the inner membrane of the mitochondrial wall).

The goal of cellular respiration is to obtain the energy from food and convert it to ATP so our body can use it for fuel.

Firstly glycolysis (splitting sugars) is the breakdown of glucose. There are 10 steps in the breakdown of glucose and fructose to pyruvate involving many enzymes. Two ATP molecules are required to fuel this process creating a 6-carbon sugar diphosphate molecule, which then splits into two 3-carbon molecules. These are then converted to pyruvate and ATP is formed. This is used during short high intensity movements and does not require oxygen (anaerobic).

The net result of glycolysis is 2 molecules of ATP, 2 molecules of pyruvate, 2 molecules of water and 2 molecules of NADH (an enzyme that helps with the transportation of electrons that have been removed during the breakdown process, taken to the inner membrane of the mitochondria for use in the electron transport chain).

The two pyruvate molecules are either passed on to enter the Krebs cycle (in the presence of oxygen lower-intensity, longer duration exercise) or converted to lactic acid by a process called fermentation (in the absence of oxygen-higher intensity, shorter duration exercise).

The next stage is called the Krebs cycle (also known as the citric acid cycle). This happens in the mitochondria and requires oxygen. The 2 pyruvate molecules from glycolysis enter here, the Krebs cycle breaks down 1 pyruvate at a time.

This is an 8-step cycle, when pyruvate enters the mitochondria, carbon dioxide is removed, and the removal of the carbons forms an acetyl group. The acetyl group then combines with coenzyme A to form acetyl coenzyme A. Acetyl coenzyme A binds to oxaloacetate to form citric.

Acetyl coenzyme A’s role is to transport acetic acid from one enzyme to another around the Krebs cycle. Each pyruvate acid molecule that is used in the Krebs cycle yields 3 CO2, 1 ATP, 4 NADH, 1 FADH2 (double for the original glucose). The CO2 are released by respiratory exhalation. Fats, carbohydrates and proteins can all be metabolised in the Krebs cycle.

The third stage of respiration is known as the electron transport chain. This is the stage where the most amount of ATP are produced. A lot of the energy (electrons) acquired in the previous two phases is stored in NADH and FADH2. These two enzymes give up their high-energy electrons. The electron transport chain is an array of molecules, mainly proteins, built into the inner membrane of the mitochondria. NADH gives up its electrons to the first complex in the chain. The electrons then move along the chain, giving up their energy as they move from one end of the chain to the other. The energy taken from the electrons is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space. This causes an increase of hydrogen ions with all the electrons and potential energy. These hydrogen ions are then diffused through a protein complex called ATP synthase. As the hydrogen ions flow through the concentration gradient of the protein complex, ATP synthase captures their energy, converting ADP and P (organic phosphate) to make ATP. One ATP synthase complex can generate 100 molecules of ATP per second. Oxygen is the terminal protein electron receptor. When the oxygen accepts the hydrogen ions it becomes water. If no oxygen is available, the hydrogen ions cannot pass through the electron transport chain, which reduces production of ATP. This phase produces a net of 32-36 ATP.

Heavy metals, pesticides, pollution and other harmful chemicals can impede the function of the mitochondria, blocking its ability to burn fuel. Eating organic food as much as possible while supporting the liver will help reduce your toxic load. It is worth remembering that toxins are stored in fat tissue. As fat is burned for energy (oxidised) toxins will be released back into the bloodstream. This is another reason why it is essential to support the liver by eating a diet full of colourful vegetables, high in fibre and to drink lots of water to help the body eliminate these harmful toxins.

Men and Women are not the same

Here at YBP we like to look as our members as individuals. The way you eat and exercise is not just determined by body type, age, ability level, but also gender. There are many exercise strategies and nutrition programs on the market, that are generic, one size fits all. This just doesn’t work. Women are very different to men. When resting woman tend to burn more glucose than men, they also store more fat after eating, this is to preserve life-saving essential fat.

From an evolutionary perspective, more fat on a woman is beneficial during pregnancy and lactation. Storing fat on the hips and thighs (gluteofemoral fat) is thought to be in preparation for pregnancy. This gluteofemoral fat has a higher percentage of DHA, one of three omega-3 fats. The theory is that there is a higher DHA level because it is important for breast milk production and it is also essential for the baby’s brain.

Interestingly, during exercise, women burn more fat than their male counterparts. Men tend to have more visceral fat (around the organs) and woman more subcutaneous fat (under the skin). Visceral fat is linked with cardiovascular disease and insulin resistance.

Women appear to lose fat from their upper body first, for the preservation reasons already mentioned. For both sexes, fat seems to be harder to lose on certain areas on the body. For men it’s the lower abdominals and love handles, while for woman it’s the hips and thighs. This is thought to be down to the type of receptors that are attached to fat cells. Receptors are like locks for a specific key, in this case the key is a hormone called adrenaline. The hormone adrenaline attaches to the receptors initiating lipolysis (fat burning). There are several different adrenergic receptors, alpha 1, alpha 2, beta 1, beta 2 and several more. Alpha 1 and beta 1 and 2 are all lipolytic (causing fat breakdown), however alpha 2 is anti-lipolytic (inhibits fat breakdown). The hips and thighs on a woman are high in alpha 2 adrenergic receptors. The combination of alpha 2 receptors and the hormone oestrogen make it harder for women to burn fat than men (who tend to have fewer alpha 2 receptors and more testosterone). The correct training and diet programme will help shift this stubborn fat.

You may have read in other articles on YBP about the importance of keeping stress under control. High levels of stress in women can cause the hormone pregnenolone (the precursor to many hormones) to produce more cortisol and aldosterone rather than oestrogen and testosterone. Testosterone has been shown to increase fat loss, while oestrogen is linked with fat storage, although conversely it appears that oestrogen during exercise stimulates both adrenalin and human growth hormone, increasing fat loss. It has been shown that cutting calories too much is not only harmful to reproduction, but it also disrupts hormones and increases cortisol. Too much stress and not getting the correct amount of calories will increase cortisol, causing muscle breakdown, slowing metabolism and subsequently reduce fat loss, even increasing fat storage.

Studies have shown that protein synthesis is actually the same in men and women, so it is possible for women, especially certain body types, to build muscle. What makes it harder for a woman to build huge amounts of muscle, is that they have a small percentage (10 to 30 times less) of the hormone testosterone than men. This is the hormone needed to build muscle. During and after exercise testosterone levels rise, but not enough to initiate any serious muscle growth, although athletic performance is improved. Protein synthesis decreases with age. So women will naturally find it harder to build serious muscle, but it is definitely possible with the correct training and diet programme to build a strong, lean body. At YBP we have seen time and again that women who lift weights get the best results. It is important for women to train using weights, as even a small increase in muscle helps speed metabolism. Research has shown that an extra 70 to 100 calories per day are burnt for each kilo of muscle built.

Another very important reason for women to weight train is to increase the strength and density of their bones. Training with weight is a powerful preventative for osteoporosis, a disease caused by porous bones and low mineral density. Osteoporosis increases susceptibility to bone fractures. A high percentage of women get osteoporosis during their lives. Research has shown that six months of weightlifting may increase bone mineral density by as much as 15 percent. An increase in muscle will naturally cause an increase in bone density. The message is, don’t be afraid to weight train.

Damage to muscle is essential for your body to change

Minute muscle tears are created when you train, these are called micro-traumas and they are subsequently accompanied with inflammation. The micro-traumas are caused by the eccentric movement (lengthening) of a muscle, rather than the concentric (contracting/shortening) phase. The soreness you get the day or days after training is a symptom of the damage caused by exercise.

The correct rest period between training sessions is important to prevent injury. The most accepted theory is that microscopic ruptures (or lesions) within the target muscle, due to the eccentric force, cause the two major protein filaments actin and myosin to separate prior to relaxation, which promotes greater tension within the remaining active motor units. Muscle contraction occurs when actin and myosin filaments slide over one another in a series of repetitive events. Sarcomere (basic unit of muscle) damage is produced when this tension to the muscle is performed. When this happens, pain receptors (nociceptors), contained in muscle connective tissues are stimulated and sensations of pain are felt. To provoke this pain, and ultimately benefit from it, we must train with increasing levels of intensity. It is not the lactic acid that is produced during the workout that causes muscle soreness or DOMS (delayed onset of muscular soreness), but the chemical changes within the muscle, i.e. hydrogen ions.

Next day muscle soreness, is not an indicator on how hard you have trained. If you have no soreness, this does not mean you will have no results. Your body will get used to a certain movement, intensity and weight. The muscle changes its structure (grows) to prevent further damage, this is what is called the repeated bout effect. This is why it is important to follow a specific training program. Muscles will adapt over time to prevent damage and results will inevitably slow. To prevent this from happening you must change your exercise program and training concept monthly.

It is not a good idea to train when muscles are still sore, this causes overtraining. But it is possible to speed up the healing process with the correct nutrition and stretch program.


There are many types of cardio. Long/medium/short duration, light/moderate/high intensity, running/biking/rowing etc. All these types and variations have their place, depending on your goal. We have all seen those people who run for hours in a concerted effort to lose weight, or those running marathons yet are still overweight. How can this be? Especially when we are told light intensity, long duration training utilises more fat than carbohydrate, why are these people not (always) lean?

There are a couple of reasons for this. Although it is true you will burn a higher percentage of calories from fat, you won’t necessarily burn as many calories. Imagine you run at a light intensity for an hour and burn 300 calories, 50% from fat (150 calories) and then the next day you perform 30 minutes of high intensity interval training and burn 600 calories but only 30% fat (180 calories) you are still in fact burning more fat. Please note that this is a simplified example only for the purposes of clarification.

The second reason is the effect high intensity training has over the 24 to 36 hours post training. High intensity exercise has a metabolism boosting affect that light intensity training doesn’t have. This is known as EPOC (excess post exercise oxygen consumption) or after burn, which is an increased rate of oxygen intake post exercise. In some studies, this has been shown to increase by 15%. This extra oxygen helps replenish ATP, resynthesize muscle glycogen from lactate, restore oxygen levels in venous blood, muscle and myoglobin. Remember when at rest we burn almost only fat, so in this increased state of metabolism for the following 24 to 36 hours post training you will be burning more fat even at rest.

Thirdly, it is the effect that the hormone cortisol has on our metabolism. All exercise will create cortisol release. People who train in endurance type events like marathon training will produce a lot of cortisol. The more experienced a person is the less cortisol produced. High intensity training, like weight training, or interval training, with short rest periods and high intensity work interspersed, will increase plasma cortisol concentrations as well. However this type of training is performed for a shorter period of time. As already mentioned, cortisol has a catabolic effect on muscle, reducing testosterone and subsequently slowing metabolism. This is why training low intensity for hours in order to lose fat does not work.

High intensity style of exercise leads to an up-regulation of both aerobic, anaerobic and ATP-PC enzyme activity. This leads to all energy systems working more efficiently at burning calories and producing energy. There is also an increase in muscle cell organelles leading to an improved calcium balance and contractile ability.

I would like to clarify that if you are training to run a marathon light intensity long duration training is essential, and with the correct diet and supplement protocol in place you can limit muscle loss. Different cardio regimes will need to be employed for sports specific goals, but for fat loss HIIT is the recommended approach.

HIIT (high intensity interval training) involves alternating between all out exertions for a recommended time (below one minute) followed by a rest period, then performing a certain number of sets. Working for such a short duration and at such a high intensity burns predominately carbohydrate. Although it is blocked from entering the mitochondria to be used for fuel because of the increase in lactic acid that is produced when working at such high intensities. This is why at YBP we recommend a lactic acid removal phase, working at the lactic acid threshold for a specific period of time (depending on body type and goal) to allow the fatty acids to enter the mitochondria and be used for energy. We then recommend another burst of intervals to get the important EPOC effect.

Studies have shown that high intensity training produces more fat loss over time than low intensity cardio. It is also particularly good for getting rid of stubborn fat. This is thought to be down to the higher levels of post exercise fat burning, higher insulin sensitivity (meaning more carbohydrate will be stored as glycogen and not fat), higher fat oxidation by muscles, an increase in growth hormone (which, as already mentioned, aids fat loss), catecholamines (adrenalin and noradrenalin) which directly induce fat mobilisation, post exercise suppression of appetite and an increase in mitochondria (allowing more fat to be utilised at the any one time.

High intensity cardio vs low intensity cardio

You may have seen many different variations of cardio while in the gym. Some people are walking, some jogging, while you will see others all out sprinting. So which version is the best? Cardio of any type is beneficial to health, from walking to skiing, for all ages in any state of health.

Heart - like any other muscle the heart grows stronger when it is challenged and worked. Conversely if it is not worked it will become weaker. A strong heart means a decreased resting heart rate, lower resting blood pressure, improved circulation (important for nutrient delivery and waste removal) and generally means your heart doesn’t have to work as hard while at rest. Testosterone is increased during and after exercise, low testosterone has been shown to increase the risk of blood clots.

Metabolism - a consistent increase in heart rate also speeds up many processes, which are also known as metabolism. Studies have shown that the higher the intensity of cardio the greater the metabolic effect. This is due to what is known as EPOC (excess post-exercise oxygen consumption). Following exercise, EPOC is part of the process that restores and replenishes body energy stores (ATP and creatine) back to a resting state, repairs cells, balances hormones creating an anabolic environment. An increased metabolism aids weight management.


Endorphins - exercise increases the release of endorphins (feel good hormones), which have been shown to alleviate the symptoms of depression and fatigue. The hormone ghrelin, which increases appetite, has been shown, to rise when performing low intensity cardio, while the opposing hormone leptin, which decreases appetite, falls, making you hungrier. Interestingly studies have shown that high intensity training decreases ghrelin concentrations, helping to curb appetite and subsequently aiding fat loss and weight management.

Human growth hormone (HGH) - as well as sporadically during the day and when we are sleeping, high intensity training has also been shown to help increase human growth hormone (HGH). HGH contributes to fat loss by aiding muscle tissue growth, which in turn increases metabolism. It has also been shown that high intensity training as opposed to low intensity increases cell sensitivity to the appetite suppressing hormone leptin up to 48 hours post training. As well as contributing to bone and muscle strength, HGH also regulates fat metabolism.

Irisin – a hormone known as Irisin (the exercise hormone) was shown in one study to reprogramme fat cells to burn rather than store fat, in another it was shown to regulate undifferentiated stem cells to become bone building cells instead of fat storage. On another note people with higher amounts of irisin in their blood were more likely to have longer telomeres (caps at the end of chromosomes). This is significant because shorter telomeres are associated with health issues such as heart disease, Alzheimer’s and cancer.

Testosterone - the male sex hormone (women also have testosterone, though in smaller amounts) is increased during exercise, especially when working large muscle groups. It is needed for bone, hair and muscle growth as it repairs muscle cells damaged through exercise. As muscle is biologically more active than fat, the more muscle the faster the metabolism.

Oestrogen - is an important female sex hormone needed for the development of breasts, for reproduction and the menstrual cycle. Like most hormones it has to be in the correct balance. Both oestrogen and progesterone decline with age, however progesterone declines more creating an oestrogen dominance. It’s a vicious cycle because an increase in oestrogen leads to an increase in fat, which in turn produces more oestrogen. Progesterone stimulates fat burning, and is also a diuretic, while oestrogen increases water retention. Too much oestrogen is associated with breast, endometrial, prostate, colon and ovarian cancer. Conversely progesterone slows cancer growth. Other symptoms include, weight gain, excessive menstruation, thyroid problems, headaches, fatigue, hot flushes, infertility, depression, endometriosis and uterine fibroids to name a few.

Oestrogen dominance could also be due to other factors:

  • Xenoestrogens – found in skin care products, some food dyes, industrial materials and pesticides to name a few.

  • The contraceptive pill

  • Obesity - due to an increased oestrogen production.

  • Stress – cortisol is the stress hormone and when elevated it uses up a hormone called pregnenolone, which is needed to produce progesterone. It also depletes magnesium, vitamin C, and B vitamins needed to neutralise bad oestrogen metabolites in the liver.

  • Heavy metals - slow liver detoxification function, which in turn leads to an increase in hormones that should have been eliminated.

  • Liver problems – for the reasons outlined above.

  • Blood sugar imbalances – these increase both insulin and cortisol, which subsequently increases oestrogen release, depletes magnesium, vitamin C, and B vitamins needed to neutralise bad oestrogen metabolites in the liver.

  • Hormone replacement therapy (HRT) - synthetic oestrogen.

  • Poor sleep - increases cortisol and when this is elevated it uses up a hormone called pregnenolone, which is needed to produce progesterone.

  • Caffeine - increases oestrogen production, depletes magnesium, vitamin C, and B vitamins needed to neutralise bad oestrogen metabolites in the liver.

Cortisol - also known as the stress hormone, it is released in large quantities when we are anxious and stressed. Ironically cortisol is a catabolic hormone, and when released in a short period it will increase fat burning. Chronic stressful lifestyles however panic our body into thinking the constant circulating catabolic hormone will use up our important energy reserves so it up-regulates the fat receptors on cells (especially around the abdomen) subsequently increasing fat storage. Studies have shown that low intensity training will either lower cortisol levels or they will stay the same. High intensity training was shown to acutely increase cortisol levels, returning to normal after exercise. Intense endurance training has been shown to chronically increase cortisol levels. Vitamin C can help reduce cortisol levels.

Peptide YY - is secreted in the gut, and acts upon the brain increasing satiety after a meal. It appears that exercise increases peptide YY levels.


Exercise increases the muscles ability to utilise glucose helping to balance blood sugar and prevent blood sugar swings. This is extremely important with diabetics as they struggle to control blood sugar. Low testosterone may also be a contributing factor.


Low intensity cardio (such as a walk after a workout) helps to remove by-products of exercise and decrease recovery time. It can also help to increase blood flow and therefore oxygen and nutrients to muscles speeding up the repair and replenishment phase, reducing DOMS (delayed onset of muscular soreness).

Different types of cardio training

There are two types key types of cardio training, low intensity and high intensity.

What is low intensity cardio?

Low intensity training is often a favourite of bodybuilders, who perform very slow, low intensity cardio for a long period in the belief they will be solely working in the fat burning zone and prevent any muscle breakdown. Working at 50-70% of your maximum heart rate (MHR) while walking, swimming or light jogging are all examples of low intensity cardio. To calculate your MHR subtract your age from 220. A person of 40 working at 50% of maximum heart rate would be working at 90 beats per minute, this is known as the fat burning zone.

It is true that a higher percentage of fuel burned during low intensity cardio comes from fat. Walking at 2.5 miles per hour burns 257 calories per hour and a low intensity bike ride will burn 343 calories per hour (based on an 80kg person). Low intensity exercise is aerobic, meaning it uses oxygen. If you are training for a long-distance event like the marathon then low intensity cardio is what you should be doing accompanied with the correct exercise and nutrition plan. Simply breathing produces free radicals (reactive unchained molecules), and the harder we breathe the more we produce. Conversely, exercise also produces the antidote, namely antioxidants. The lower intensity training however produces more antioxidants compared to free radicals, while the opposite is true of high intensity training, making lower intensity training better for the immune system.

What is high intensity cardio?

High intensity cardio is performed at 70-90% MHR and works in the anaerobic (without oxygen) energy systems (ATP-PC and glycolysis) using short intense bursts with ATP replenishment rest in-between. The fuel used in these particular energy systems comes predominantly from stored carbohydrate (glycogen). There is a limited supply of glycogen, around two hours depending on weight. High intensity workouts include short explosive bursts of energy, sprints for example. You will never be exclusively burning one fuel whilst training, it is true that working at this intensity there will be an inevitable use of protein as an energy source and this will be taken from muscle tissue, as the body simply cannot break down fat fast enough. This will subsequently lead to a loss of muscle tissue, however due to the hormonal response elicited from this type of training (an increase in testosterone and HGH) it has also been shown to aid muscle growth. As long as the high intensity training is accompanied with the correct nutrition and nutrient timing, there should be no muscle loss. Insulin is the anabolic hormone needed to take sugar from the bloodstream and push it into cells, to be either used for energy or stored as glycogen or fat. Insulin sensitivity (how well your body processes glucose and stores body fat) is improved through high intensity training. The more insulin sensitive your body, the smaller the amount of insulin required to balance blood sugar, preventing an overreaction and increased fat storage. As well as the negative affect this style of training has on the immune system (mentioned in the previous section), another negative is the parallel increase of lactic acid with intensity. An increase in acidity will cause the body to leach alkaline reserves in the form of minerals from bones to buffer the acidic environment. This however is not a reason to avoid this type of training. With the correct nutrition plan in place you can ensure you are getting plenty of alkalising foods and antioxidants to counteract the negative aspects of high intensity training, although if you are already feeling under the weather you will be better choosing the low intensity option until you are recovered.

Which is best for fat loss, low or high intensity cardio?

A woman weighing 60 kg working at low intensity (60-65% of MHR) for 30 minutes burns 146 calories, 73 calories from fat (50%).

The same woman performing high intensity training (80-85% MHR) for 30 minutes burns 206 calories, 82 from fat (39.8%).

This shows that although a higher percentage of calories burnt at low intensities come from fat, working at a higher intensity actually burns more calories and subsequently a higher portion of fat.

High intensity training, by its nature is hard due to the energy system you will be working in. This type of training can only be performed for shorter periods of time. It is important to remember that training at high intensity on a regular basis can lead to overtraining and injury. Make sure you stretch and listen to your body. High intensity training is best for results, but it is worth throwing in the odd low intensity, recovery session. Recovery will be faster with low intensity training.

High intensity training has been shown to increase mitochondria concentrations in muscle. This is significant because mitochondria are the organelles found inside cells that burn fuel for energy. The fitter you become, the more mitochondria you will have, the more energy we can burn at one time, making our workouts more efficient. Another added benefit with the high intensity training is the EPOC factor previously mentioned in this article.

Fat burns in a carbohydrate flame

This simply means that when glucose reserves are depleted from both the blood and stores (glycogen), exercise becomes difficult, as you will fatigue. Fat is metabolised very slowly and will only sustain low to moderate intensity exercise, and as you will see in the cardio section intensity is key.

As we begin exercise we will predominantly be using glucose for fuel regardless of the intensity. When we are oxidising glucose for energy, intermediates are produced (see the energy system section) to allowing acetyl CoA group to enter the krebs cycle. Acetyl CoA is produced from fat (beta oxidation) and carbohydrate (glycolysis) breakdown. Acetyl CoA then enters krebs cycle, where the acetyl portion is oxidised to carbon dioxide and water releasing energy as ATP and GTP. It is the intermediates produced during glucose breakdown that allows fat to be used for energy. Different body types on differing goals may fuel themselves in different ways before training. Some are better eating 45 mins to 1 hour before, while others are better to have a 2 to 3 hour window of not eating before training. It is important to replenish glycogen stores post training and eat the right amount of carbohydrates to ensure you have enough to train at the right intensity. The amount of carbohydrate you eat depends on your daily activity level, your goal, how many times you exercise per week, your body type and your stats. If you have dinner at 7pm and breakfast at 7am that is 12 hours without food. We burn on average 100 calories an hour so that is 1200 calories burnt throughout the night. At rest or below 65% of aerobic capacity, 50% or more comes from fat. We can’t access muscle glycogen (roughly 1,500 calories) while at rest so all our energy during this time comes from fat, blood glucose (roughly 80 calories) and liver glycogen and fat. We store anything between 50-120g (200-480 calories) of glycogen in the liver. This means that by the morning liver glycogen stores are very low, if not depleted. This is more of an issue for the ectomorph body type. An ectomorph will have a smaller storage capacity than other body types and a faster metabolism depleting their small stores. Once the glycogen stores are depleted, the body will start to obtain the extra energy required from fat and protein (from muscle). The endomorphic body type need not worry as much. They will have a larger capacity to store glycogen, they tend to build and maintain muscle much easier and they have a slower metabolism so will not burn as much glycogen, which is great for preventing muscle breakdown, but not for fat loss. It is however better to ensure glycogen stores are replenished regardless of body type. For the ectomorph it prevents muscle breakdown and subsequently slowing of the metabolism, and for the endomorph it supplies the body with the correct fuel to exercise at high intensities without fatigue. This is why it is essential to replenish your stores after training when you are most insulin sensitive and eat the correct amount of carbohydrates during the day.

On the other end of the scale, overeating carbohydrates, not only in general, but also per meal, can cause an energy surplus. In the energy surplus scenario, once muscle and liver glycogen stores are full, the excess glucose will be converted to fat (lipogenesis).

It is easy to over or under-eat. We are not suggesting people should be constantly counting calories, however, we do think that monitoring your calorie intake for a couple of weeks makes a huge difference to really understanding what you are eating. It is essential to tailor your calorie and macronutrient intake to your specific body type, goal, daily physical activity level and your personal statistics (age, weight, height).