If you have been lifting for a while, we're sure you will have heard the terms being in an anabolic or catabolic state.

If you have but aren't sure exactly what this means, anabolism is simply the constructive phase of metabolism in which the body's cells synthesize protoplasm for growth and repair. Conversely, catabolism is the destructive process wherein muscle and other complex substances are broken down into simpler compounds.

With that in mind, if you are looking to build muscle, improve your body composition and lose weight, then understanding how to maintain an anabolic state and ward off catabolism are crucial. In this guide, we are going to cover the major factors of the endocrine system and their role in protein anabolism and catabolism.

Before we get into that, we need to understand a bit more about the human body. Let's start with metabolism.

The basics of metabolism

We're sure most people know the term ‘metabolism’ and get the gist of what it is, but let's get a bit deeper into understanding exactly how it works.

All life is made up of cells and within these cells, chemical reactions are constantly occurring. As these reactions occur, the cells both utilise and give off energy. These reactions are divided into two categories, namely anabolic and catabolic. Anabolic reactions use energy to build cell components and molecules while catabolic reactions give off energy as they break down complex substances.

The process of metabolism refers to these reactions within the cells which occur to sustain life. Metabolism is impacted by several variables which include physical activity, nutrient availability, hormone signaling, and energy status. These affect how and when these reactions will occur. The process of metabolism creates an inherent input and output of energy, thus the need for nutrients.

Body Composition

To achieve an aesthetically pleasing physique, we need to improve body composition. This is done by reducing fat and increasing lean muscle mass. The problem with us as humans is that we want quick results, but unfortunately, losing fat and building muscle simultaneously is not likely.

This is because these events are theoretically mutually exclusive. Losing weight requires an energetic deficit while building muscle requires an energetic excess. Think about it this way, if you want to build muscle, you need to consume a surplus of calories to bring about the cellular reactions required to grow and repair muscles, and if you are eating a large number of calories, chances are that you will not be able to lose body fat. It is for this reason that bodybuilders approach training with periods of building muscle (bulking) and periods of losing body fat (cutting).

Now that we understand exactly how to go about improving body composition, let's have a closer look at how protein anabolism and catabolism impact on this.

Learning The Jargon

Before we get into the meat of the article, we are going to need to learn a few technical terms to help us understand the effects of anabolism and catabolism.

  • Muscle Protein and Synthesis (MPS) - This refers to the synthesis of protein in muscle tissue.
  • Muscle -  Protein Degradation (MPD)Refers to the breakdown/degradation of muscle tissue
  • Protein Turnover - The measurement that detects the balance between protein synthesis and protein degradation
  • Muscle Protein Anabolism - The state in muscle tissue where synthesis exceeds degradation and thus, lean tissue is being broken down
  • Muscle Protein Catabolism - The state in muscle tissue where degradation exceeds synthesis, and thus, lean tissue is being broken down.
  • Hypertrophy - Growth of tissue, in this case, muscle tissue.
  • Atrophy - Tissue shrinkage, in this case, muscle tissue.

Factors And Hormones That Affect Muscle Protein Anabolism And Catabolism

Now that you have an understanding of metabolism, body composition and know the jargon, we can get into the factors which play a large role in protein anabolism and catabolism; and which ultimately affect body composition. Here are some of the factors and hormones which we will be addressing.

As we run through each factor and hormone, you must keep in mind that these aspects have a certain degree of the interplay among one another so it is nearly impossible and also impractical to isolate these components in an everyday setting.

Amino Acid Pooling, Transport And Oxidation

In the human body, muscle tissue makes up the largest reservoir of amino acids and the largest mass of protein. The two main amino acid pools we are concerned with here are the circulating and intracellular pool.  When the body is in a catabolic state, amino acids are released from muscle tissue into circulation to be used by other bodily tissues. However, when the body is in an anabolic state, amino acids can be transported from the circulation into the intracellular space of muscle cells. They can then be incorporated into proteins and thus, synthesize new protein. Protein anabolism is also controlled, in part, by the transport of amino acids into and out of muscle cells.

Amino acids provide a substantial amount of energy due to oxidation. The oxidation of amino acids to ammonia and carbon occurs during states of starvation, when there is excessive protein in the diet and when carbohydrates are vastly restricted. The ammonia that is produced is excreted as urea via the kidneys and the carbon enters the citric acid cycle for the production of energy.


This peptide hormone is secreted in the pancreas mainly in response to increases in blood sugar levels. While insulin has got a bad rap for its ability to cause weight gain if elevated correctly and at the right times, insulin can be a powerful muscle-building tool. It is an extremely anabolic hormone that acts to induce protein anabolism when amino acids are replenished. The key to maximizing this anabolic effect is to elevate insulin levels while providing the body with enough amino acids to kick-start protein synthesis.

While research suggests that insulin doesn't directly affect the rate of transport of most amino acids, it does indicate that it increases muscle protein synthesis by drawing on the active intracellular pool of amino acids. The exceptions to this are amino acids like alanine, leucine, and lysine that use sodium-potassium pumps as insulin causes muscle cells to become hyperpolarized by the activation of these pumps. What this suggests is that hyperinsulinemia (i.e. excess levels of insulin in the blood relative to the level of glucose) coupled with elevated plasma amino acid levels is favourable for facilitating muscle protein synthesis. This can be induced by simply consuming protein and carbs.

IGF-1 is a peptide hormone that is produced mainly in the liver. It binds with growth hormone and therefore influences the growth of humans, meaning IGF-1 is a mediator of the effects of GH. IGF-1 is also a potent initiator of the AKT signaling pathway in cells, which impacts cell growth and the proliferation thereof. Because IGF-1 is bound to one of six protein complexes in the body, we need to factor in the actions of IGFBP-3 as this makes up roughly 80% of all the binding.

Insulin-Like Growth factor-1 (IGF-1) & IGF-Binding Protein-3 (IGFBP-3)

Similarly to insulin, IGF-1 affects protein metabolism due to its ability to bind and activate the insulin receptor. However, this occurs at a far less effective rate as IGF-1 only has about 1/1oth of the potency of insulin. Between IGFBP-3's ability to inhibit skeletal muscle atrophy and IGF-1's ability to promote protein anabolism in skeletal muscle, increasing the production of these anabolic hormones will position you for greater gains in lean muscle mass.

Factors that affect the production of IGF-1 and IGFBP-3 include, but are not limited to, genetics, biorhythms, age, exercise, nutrient status, stress, disease state, and ethnicity.

As growth hormone is ultimately what leads to IGF-1 production, if we elevate endogenous GH levels, we will subsequently enhance IGF-1 production. We will discuss practical ways to increase the production of GH in the next section.

Growth Hormone (GH)

This peptide hormone which is produced in the pituitary gland is responsible for the stimulation of cell growth and reproduction. GH also stimulates the production of insulin and IGF-1. This subsequently promotes the growth of lean body mass, adipose tissue, and storage of glucose. When the body is in a fasted and other catabolic states, GH then stimulates the release and oxidation of free fatty acids for energy and consequently preserves lean body mass and glycogen stores. This oxidation of free fatty acids may also help with weight-loss.

The growth hormone's anabolic actions work mechanistically differently to that of insulin. While insulin's anabolic actions occur during the preprandial timeframe, GH's anabolic actions tend to occur during stress and fasting.

The growth hormone also inhibits the oxidation of amino acids. This means that GH spares vital amino acids in the amino acid pools which results in greater availability of amino acids for incorporation into proteins.

In the short term, GH also helps to promote protein synthesis. This occurs as a result of the downstream paracrine IGF-1 release. But it is not just GH that helps to increase paracrine IGF-1, testosterone is also responsible for amplifying IGF-1 levels.

Another great benefit of increased GH is that it accelerates the transport of numerous essential amino acids across the cell membrane. These are specifically the essential amino acids that are mediated by System L (the major transport system responsible for sodium-independent transport of neutral amino acids) such as leucine, isoleucine, and valine.

To Maximise GH, You Can Consider the Following List of Stimulators and Inhibitors:

Stimulators of GH Secretion

  • Sex hormones (androgens and oestrogen)
  • Peptide hormones such as ghrelin and growth hormone-releasing hormone (GHRH)
  • Nicotinic acid (Vitamin B3)
  • Nicotinic receptor agonists Somatostatin inhibitors
  • Fasting
  • Deep sleep
  • Intense exercise
  • GABA (gamma-aminobutyric acid) supplements

Inhibitors of GH Secretion

  • Somatostatin
  • Hyperglycaemia ( e.g. carbohydrates in the bloodstream)
  • IGF-1 and GH (due to negative feedback inhibition on the pituitary gland)
  • Xenobiotics
  • Glucocorticoids
  • Certain sex hormone metabolites, such as dihydrotestosterone (DHT)


It also stimulates the production of insulin and IGF-1. This subsequently promotes the growth of lean body mass, adipose tissue, and storage of glucose.


Androgens are anabolic hormones that influence the development and maintenance of male sex organs and secondary sex characteristics. While there are several androgens produced in the adrenal glands, the one we are going to focus on is testosterone. This is because it is the most potent naturally produced anabolic hormone.

Testosterone has been shown to play a central role in the growth and maintenance of muscle tissue. Studies in which hypogonadal men (i.e. men with testosterone deficiency) were given a replacement dose of testosterone, saw the men experience gains in fat-free mass and muscle strength with an increase in muscle protein synthesis. This effect was also seen in healthy men and trained athletes upon the administration of pharmacological doses of various androgens.

Similar to GH, testosterone also appears to exert part of its anabolic effect by decreasing amino acid oxidation and enhancing uptake into muscle proteins. Additionally, there is also a synergistic, but independent, anabolic effect between testosterone and growth hormone which enhances their benefits on muscle protein synthesis (MPS).

To maximise the production of testosterone, you can consider the following list of positive and negative effectors.

Positive Effectors

  • Adequate sleep
  • Fat loss (to a degree, since fat cells secrete aromatase, an enzyme involved in the production of oestrogen.)
  • Vigorous exercise (especially resistance training) Testosterone-boosting supplementation (ZMA, DAA, Ashwagandha, Tribulus Terrestris)

Negative Effectors

  • Obesity
  • Lack of sleep
  • Sedentary lifestyle / inactivity
  • Very-low fat diets
  • Prolonged aerobic/cardiovascular exercise
  • Excessive alcohol intake
  • Xenobiotics

Oestrogenic Hormones

Oestrogens are the primary female sex hormones that are responsible for the growth and maturation of female reproductive tissues. Just like females produce testosterone, males also produce oestrogen, but in much lower concentrations.

The 3 major oestrogens produced in the steroidogenesis pathway are oestradiol, oestrone, and oestriol. Oestradiol has the most potent oestrogenic effects, roughly 10 times that of oestrone and 80 times that of oestriol.

While most oestrogens in females are produced in the ovaries via aromatization of androstenedione, in males it is produced from the testes and more so in the aromatization of testosterone in fat cells.

Oestrogens can have both anabolic and catabolic effects with regards to protein metabolism. However, these occur mainly through the mediation of other hormones in the body. Oestrogens increase systematic GH levels and paracrine IGF-1, both of which favour anabolism. Oestrogens also promotes water retention which is favourable to cell volumisation, and therefore anabolism.

On the other hand, when there is an excessive amount of oestrogen present in the body it can be indirectly catabolic as its backload’s androgen receptors and down-regulate the production of gonadotropin-releasing hormone in the hypothalamus. This will result in lowered testosterone production.

To keep a balanced oestrogen production, follow these tips:

  • Eat a well-balanced diet that has sufficient vitamins/minerals and dietary fibre.
  • Limit the intake of soy and phytoestrogens from plant products.
  • Limit alcohol intake as this impairs the liver's ability to metabolize oestrogens.
  • Supplement with anti-aromatase inhibitors/oestrogen blockers (DIM & Eurycoma Longifolia)
  • Maintain a regular workout/exercise regimen.
  • Maintain healthy body weight.

Oestrogens can have both anabolic and catabolic effects concerning protein metabolism. However, these occur mainly through the mediation of other hormones in the body.

Stress Hormones

Glucocorticoids (primarily cortisol), glucagon and catecholamines

Glucocorticoids (mainly cortisol), glucagon and catecholamines (specifically epinephrine/adrenaline) are secreted in response to stress.


This steroid hormone is produced in the adrenal glands. It is responsible for the regulation of metabolism, development, immune function, and alertness. The main glucocorticoid produced in the body is cortisol. Cortisol is commonly known as the "stress hormone" and is often demonised for its ability to promote muscle atrophy. During periods of fasting, cortisol maintains nominal concentrations of glucose in the blood by initiating gluconeogenesis. However, to aid this process, amino acids get utilised and protein then gets degraded.


This peptide hormone is produced in the pancreas. It works in reverse to insulin. For example, glucagon stimulates glucose released when blood sugar levels drop. Glucagon also influences gluconeogenesis and also glycogenolysis, similar to cortisol.


The main hormone that falls under the catecholamines is adrenaline (epinephrine). It is often referred to as the fight-or-flight hormone. Adrenaline is produced in the central nervous system and adrenal glands. Like cortisol and glucagon, adrenaline also stimulates glycogenolysis in the liver and muscle.

Under prolonged periods of stress, these hormones impair muscle protein synthesis. This leads to muscle tissue atrophy. Adrenaline and cortisol may also inhibit the secretion of insulin and blunt the synthesis of paracrine IGF-1, both of which are anabolic hormones. This is then counterproductive to the protein anabolism.


This guide to protein anabolism and catabolism falls in a field of research that is continually growing.

Therefore, advances in discovering exactly how these hormones work and how best to manipulate them to enhance protein anabolism are undergoing constant change. However. this guide gives you a broad overview of the factors that mediate protein metabolism and our goal is to provide you with the necessary information to devise the optimal eating and lifestyle habits required to maximise protein anabolism and therefore build more muscle.

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