Many bodybuilders consider protein to be the most important part of the diet. While essential for building muscle, protein alone will not create a great physique. A combination of good quality protein with optimal amounts of other macro- and micronutrients along with an effective training regime will allow for maximal results.

Performance-Meals are high in protein.

What is protein?

Protein molecules are long chains of constituent amino acids, joined together by ‘peptide’ bonds. There are 20 standard amino acids that can be joined to form proteins. The combination of different amino acids in the chain, along with the relative numbers of each in the protein will determine the overall structure of the protein and therefore its purpose.

The 20 amino acids used in protein are listed below. Those in italics are deemed essential because they cannot be created in the body from other amino acids in a process called transamination. They must be obtained from the diet, or deficiency will result:





















There are other, non-protein amino acids such as ornithine and taurine, which have their own particular biological functions. Indeed, many of the above standard amino acids also have non-protein functions in the body, as discussed below.

Uses of protein

  • Structural – the most well known and bodybuilding related fate of dietary protein is incorporation into muscle tissue. A diet rich in protein (balanced by adequate amounts of carbohydrate, fat and micronutrients) combined with weight training can result in hypertrophy. Other common structural proteins are: collagen, responsible for giving skin its structure and elasticity and keratin, present in hair and nails.
  • Enzymes – these are long molecules of protein twisted into characteristic globules, each one specific to the action of the individual enzyme. Enzymes are responsible for speeding up (catalysing) metabolic reactions. For example, amylase is an enzyme that facilitates the digestion of starch into smaller molecules in the mouth and in the upper intestine.
  • Oxygen transport molecules – these have a similar structure to enzymes and facilitate the carriage of oxygen around the body in the bloodstream (haemoglobin) or in the muscles (myoglobin).
  • Hormones – some hormones, such as growth hormone, insulin and glucagon are peptides. These play a key role in anabolism and fasting.
  • Immune system – some immune systems factors are made up of proteins.

Uses of amino acids

While the majority of amino acids are incorporated into protein to fulfil the above functions, some individual amino acids have particular roles in the body, which include:

  • Glycine is used in the production of creatine (muscle function), haem (oxygen transport and the final part of respiration) and glutathione (a potent antioxidant). While glycine itself is not essential, it may be required in such quantities the requirements cannot be met by transamination alone. Therefore, a dietary source is required. Glycine therefore may be considered ‘conditionally essential’.
  • Lysine is required to synthesise carnitine, a molecule (an amino acid itself) used to transport fat into the sub cellular organelles for oxidisation.
  • Arginine is metabolised to form nitric oxide, which plays an essential role in the tone of blood vessels, blood pressure, neurotransmission and immune function.
  • Tryptophan is used in the synthesis of serotonin, which is why consuming tryptophan rich foods before bed such as milk or cottage cheese may help you sleep, although only when consumed with carbohydrate, so not necessarily ideal for the bodybuilding enthusiast.

Many other amino acids have such vital functions in the body. However, supplementing with these aminos will not necessarily result in the more creatine or more fat being oxidised, as the body has to be deficient in these nutrients at the outset. Adding in more, when more are not required will just be surplus calories.

Incorporating protein into the bodybuilding diet

Unlike carbohydrate and fat, protein is a key feature of every meal in a bodybuilding diet, whether bulking or cutting. It really is as simple as that. The amounts required will vary from person to person. Some will gain mass on relatively low levels, others will need significantly more.

Start out with around 2g per kg bodyweight a day and adjust accordingly. If gains are slow, try increasing the protein levels consumed, if too much fat is gained, try decreasing the levels of protein (while still ensuring balance with other macronutrients).

There is much talk of the biological value (BV) of protein. This is a measure of the percentage of protein ingested that is stored in the body. Whey protein has the highest biological value, with egg a close second. Further down the list is milk, followed by fish, beef, chicken, soy and pulses. This method of characterising protein has significant flaws, such as ignoring the amino acid profile of a protein (which effectively could have a high biological value but lack an essential amino acid) and is disputed in the scientific literature.

When bulking, eat as much of your protein from food sources (with the exception of whey post workout or first thing in the morning), keeping them relatively lean (grilled chicken and turkey, lean cuts of red meat, white fish, tuna, low fat cottage cheese, pulses, egg whites, etc) or containing healthy fats (oily fish). However, for those with high protein requirements but not so big appetites, meal replacement protein shakes can be a useful addition.

While cutting, protein intake remains similar to when bulking and therefore forms a greater overall percentage of calories, given that carbohydrate and fat are restricted. However, the sources must on the whole be food based (apart from whey post workout) and very lean, unless contributing to essential fats.


While whey protein and in some cases, meal replacement protein shakes, are a notable addition to a bodybuilding diet, adding easy to eat protein, there are many more protein based supplements on the market offering in some cases miracle results overnight.

These are covered in more detail in the supplements article. However, scientific evidence of the efficacy of such supplements e.g. branched chain amino acids (BCAA), glutamine, etc is equivocal. While they may be of benefit to some individuals it would be advisable to work on the overall diet first, to ensure sufficient levels of nutrients from real foods rather than using supplements to correct for an inadequate diet.


While protein plays an important role in the bodybuilder’s diet, the contribution of other macro- and micronutrients cannot be underestimated. Combining large amounts of whey protein and other supplements with a junk food diet and inappropriate training will not create the desired physique.



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