Protein quality can be determined on the quantity of the essential amino acids in the protein. Leucine, one of the essential amino acids, is an important stimulus for protein synthesis.
The protein quality of a product can be determined on the basis of three characteristics:
- the quantity of protein in a food;
- the quantity of essential amino acids in the protein;
- the digestibility of the amino acids in the protein in the intestine and, consequently, the availability for absorption by the body. (1)
For athletes adequate protein with sufficient essential amino acids is important for supporting the development and maintenance of muscle mass. Additionally, the essential amino acid leucine, together with insulin and exercise training, is an important stimulus for protein synthesis.
Essential amino acids
9 out of the 20 amino acids that make up proteins are essential amino acids. The daily need for every essential amino acid has been determined (FAO/WHO/UNU, 2007). For an adequate intake of all essential amino acids it is important to consume a combination of various protein sources on a daily basis, as the quantity and composition of essential amino acids differs for each protein source. Foods with high quality proteins provide more essential amino acids.
Particular essential amino acids are important for optimum protein synthesis. The body cannot make the essential amino acids itself and therefore these must be obtained from food.
Studies among younger athletes show that eating 20 grams protein in combination with strength training is adequate to maximise muscle protein synthesis. The 20 gram protein source must be high quality and contain a sufficient amount of the essential amino acid leucine. (2-4) For the elderly a combination of proteins with a high content of essential amino acids in particular a high leucine content seems to be the best choice to support protein synthesis. There is also evidence to suggest that the quantity of protein required for optimum protein synthesis is about twice as high for elderly people as it is for younger people. (5)
- Tomé D. (2012). Criteria and markers for protein quality assessment – a review. British Journal of Nutrition. 2012;108,S222–S229.
- Moore D.R., Robinson M.J., Fry J.L., Tang J.E., Glover E.I., Wilkinson S.B., Prior T., Tarnopolsky M.A., Phillips S.M. (2009). Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise response of muscle and albumin protein synthesis after resistance exercise in young men. American Journal of Clinical Nutrition. 2009;89:161-168.
- Churchward-Venne T.A., Burd N.A., Mitchell C.J., West D.W., Philp A., Marcotte G.R., Baker S.K., Baar K., Phillips S.M. (2012). Supplementation of a suboptimal protein dose with leucine or essential amino acids: effects on myofibrillar protein synthesis at rest and following resistance exercise in men. The Journal of Physiology. 2012;590.11:2751–2765.
- Devries M.C., Phillips S.M. (2015). Supplemental Protein in Support of Muscle Mass and Health: Advantage Whey. Journal of Food Science. 2015;Vol 80(S1). doi: 10.1111/1750-3841.12802
- Wall B.T., Cermak N.M., van Loon L.C.J. (2014). Dietary Protein Considerations to Support Active Aging. Sports Medicine. 2014;44(S2):S185-S194.