Protein, one of the three macronutrient groups, along with lipids (fats) and carbohydrates. The role of protein for muscle growth and repair is well documented; however it is also essential for the maintenance of healthy bones, skin and ligaments/ tendons.

Research published by Stark et al. on  reports that:

“For maximal muscle hypertrophy to occur, weightlifters need to consume 1.2-2.0 grams (g) protein per kilogram. (kg) and > 44–50 kilocalories (kcal). Kg body weight daily”.

A diet containing more than 2g/kg/day is typically considered a ‘high protein diet’. When calculating macro breakdown, whatever our goals, we apply 4 calories per gram.

However, apart from calculating protein amounts to optimally achieve our goals, what other considerations must we give to protein foods?

Biological Value

Biological Value (BV) is a measurement of the ability of our body to make use of amino acids in foods.  It is one of a number of measures by which protein quality is considered. The higher the BV of a protein source, the greater the capacity for our body to make use of the amino acids.

Table 1, below, shows some protein sources with the highest biological values. Quoted from an article on, the biological value is calculated by:

“Biological value measures protein quality by calculating the nitrogen used for tissue formation divided by the nitrogen absorbed from food. This product is multiplied by 100 and expressed as a percentage of nitrogen utilized”

Table 1:

  • Cow’s Milk Biological Value:  91
  • Casein Biological Value: 77
  • Whey Biological Value: 104
  • Egg Biological Value: 98
  • Beef Biological Value: 80
  • Soy Biological Value: 74

Amino acids

Another consideration that must be given is to the constituent components of the proteins that we consume. Amino acids are defined as:

Any of a class of organic compounds that contains at least one amino group, –NH 2, and one carboxyl group, –COOH: the alpha-amino acids, RCH(NH 2)COOH, are the building blocks from which proteins are constructed.”

There are 20 amino acids, and they comprise the basic components that proteins are built form. However, not all amino acids are equal. Amino acids are subdivided into 3 different groups: Essential, non-essential and conditionally essential. Table 2, below, categorises the amino acids.

Table 2:

Essential (Indispensable)

Histidine / Isoleucine / Leucine / Lysine / Methionine / Phenylalanine / Threonine / Tryptophan / Valine

Conditionally essential

Arginine / Cysteine / Glutamine / Glycine / Proline / Tyrosine

Non-essential amino acids

Alanine / Asparagine / Ornithine / Serine / Theanine

The 9 essential amino acids are considered so as they must be consumed though our diet. These amino acids cannot be synthesised by the body therefore the body’s supply must be provided daily by foods.

The 9 essential amino acids combine with each other within the body to create the non-essential amino acids. The third classification of ‘Conditionally essential amino acids’ are needed in times of illness and stress.  During times of stress or trauma, 6 non-essential amino acids (See table 2) become ‘conditionally essential’ (Indispensable).  During these periods of recovery, these non-essential amino acids must be supplied by the diet to meet the needs of the body.


Sources of protein

Sources of protein can be subdivided into two categories: Complete proteins and incomplete proteins.

For a protein source to be considered complete, it must contain sufficient amounts of all 9 essential amino acids. Animal sources of protein such as Beef, pork, chicken, turkey, eggs, fish and most protein supplements are all considered complete proteins.

Incomplete protein sources are generally all plant sources apart from soy. This makes soy protein an excellent complete source of protein for vegetarians. Incomplete protein sources are low or lacking one or more of the essential amino acids.

Plant based sources such as beans (kidney beans etc.), chickpeas, legumes and vegetables are considered incomplete however they can be mixed to create complete proteins.


Protein digestibility corrected amino acid score (PDCAAS)

PDCAAS numerically ranks protein sources based on the completeness of their essential amino acid content, and has a maximum score of 1.0


PDCAAS of different protein sources.

A score of 1.00 indicates that the protein source contains all 9 essential amino acids. Table 3, below, contains the same protein sources as table 1, however the PDCAAS have been included. With all but beef protein achieving a maximum score of 1.00, these are all complete sources of protein and contain all the essential amino acids in sufficient amounts.

Table 3:

Source of protein:                   BV (Biological Value)                     PDCAAS

Bovine/ Cow’s milk                         91                                                           1.00

Casein                                            77                                                           1.00

Whey                                              104                                                         1.00

Egg                                                 98                                                           1.00

Beef                                                80                                                           0.92

Soy                                                  74                                                           1.00



Branch chain amino acids (Leucine, Isoleucine and Valine) are 3 essential amino acids that comprise one third of all skeletal muscle.

Food sources of BCAA’s include chicken, fish (especially tuna and salmon), eggs and lean beef. However, BCAA supplementation has also been proven to be beneficial to resistance training athletes. To quote a report published in the ‘Journal of the International Society of Sports Nutrition’ by Campbell et al.

“When BCAAs are taken during aerobic exercise the net rate of protein degradation has been shown to decrease. Equally important, BCAA administration given before and during exhaustive aerobic exercise to individuals with reduced muscle glycogen stores may also delay muscle glycogen depletion.”

BCAA’s been shown to aid in recovery from exercise by not only offsetting fatigue but also by boosting protein synthesis.

The study by Campbell et al. as mentioned above suggests an intake of BCAA’s as follows:

Leucine: Great than or equal to 45 mg/kg/day

Isoleucine: Great than or equal to 22.5 mg/kg/day

Valine: Great than or equal to 22.5 mg/kg/day

Thus providing the optimal 2:1:1 ratio of the 3 BCAA’s.



van Hooijdonk, T [WWW]—Assessing-protein-quality-110613.pdf  “Assessing Protein quality” (2013)

Matthew Stark , Judith Lukaszuk, Aimee Prawitz and Amanda Salacinski [WWW]  “Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training”

Jose Antonio, Corey A Peacock, Anya Ellerbroek, Brandon Fromhoff and Tobin Silver [WWW]  “The effects of consuming a high protein diet (4.4 g/kg/d) on body composition in resistance-trained individuals”  (2014)

Jay R. Hoffman and Michael J. Falvo [WWW]  “Protein- which is best?” (2004)

Gertjan Schaafsma [WWW]

“The Protein Digestibility–Corrected Amino Acid Score” (2000)

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