DIETARY PROTEIN AND EXERCISE: EVERYTHING YOU NEED TO KNOW.
Recommended protein intake
Recommended protein intake is most certainly a controversial topic and one which has experienced considerable change in recent years. Currently, the recommended dietary allowance (RDA) for protein intake varies based on the individual’s physical activity level. As an individual’s physical activity increases so should their dietary intake; this is due to increased rates of amino acid/protein metabolisation during exercise (1) and damage to muscle tissue caused by exercise (2). Here are the current daily recommended ranges according to the International Olympic Committee (IOC) and the International Society of Sports Nutritionists (ISSN) (3).
- General population – 0.8-1.0g/kg body weight
- Physically active individual –1.0-1.5g/kg body weight
- Strength/resistance training individual – 1.5-2.0 g/kg body weight
How are these values calculated?
Protein recommendations are based on measurement of nitrogen balance and utilisation of amino acid tracers. Nitrogen is the fundamental component of amino acids, which are considered the building blocks of protein (4). Nitrogen balance measurement involves tracking the total amount of nitrogen which is consumed vs the amount which is excreted; when an individual is in nitrogen balance they are considered to be consuming and excreting an equal amount of nitrogen, therefore their dietary intake meets nutritional requirements (5).
Protein consumption and kidney function
One of the common things you’ll hear in the media is that high protein consumption causes kidney failure, reportedly due to the increased strain placed on the glomerular pressure and filtration systems (6). The research which cited these issues was conducted in individuals already with renal disease, and the dots were connected to healthy individuals. Significant research has been done into this area with healthy individuals since nothing has been proven (7, 8, 9, 10).
Protein consumption and calcium
Another commonly held belief is that high protein consumption affects calcium retention, which could predispose an individual to osteoporosis. This again has been extrapolated from studies with small sample sizes and methodological errors. Recent research has shown that the phosphate content of foods is protective against bone resorption (11).
Another topic which gains a lot of attention around protein intake is timing, specifically for exercising individuals who are performance or body composition focused. It is agreed that protein timing is essential for recovery, inducing hypertrophy, glycogen resynthesis, and perhaps maintenance of proper immune function (12).
This article’s aim is not to go into a detailed analysis of pre, intra, post-workout protein timing and amounts - that would be another article altogether!
Branched-Chain Amino Acids
The branched-chain amino acids (BCAAs) are three of the nine essential amino acids, specifically leucine, isoleucine, and valine. A significant body of research has stated the benefits of BCAAs on muscle protein synthesis (13), which has led to a range of BCAA supplements becoming popular.
The benefits and applicability of a BCAA supplement depend on an individual’s exercise habits and dietary patterns, along with other factors. For individuals consuming a low protein diet, BCAA supplementation can prove to be beneficial in promoting muscle retention and growth; this supplementation can be either during or after exercise (14). However, for individuals with an already high dietary protein intake (>1.5 g/kg/day) supplementation has been shown to be ineffective due to an already high BCAA content from whole food sources (15).
1. Rennie, M. J., Edwards, R. H. T., Krywawych, S., Davies, C. T. M., Halliday, D., Waterlow, J. C., & Millward, D. J. (1981). Effect of exercise on protein turnover in man. Clinical Science, 61(5), 627-639.
2. Potgieter, S. (2013). Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the
3. International Society for Sports Nutrition. South African journal of clinical nutrition, 26(1), 6-16. (3)
Tarnopolsky, M. (2004). Protein requirements for endurance athletes. European Journal of Sport Science, 4(1), 1-15.
4. Wu, G. (2013). Functional amino acids in nutrition and health.
5. Rand, W. M., Pellett, P. L., & Young, V. R. (2003). Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. The American journal of clinical nutrition, 77(1), 109-127.
6. Metges, C. C., & Barth, C. A. (2000). Metabolic consequences of a high dietary-protein intake in adulthood: assessment of the available evidence. The Journal of nutrition, 130(4), 886-889.
7. Martin, W. F., Armstrong, L. E., & Rodriguez, N. R. (2005). Dietary protein intake and renal function. Nutrition & metabolism, 2(1), 1-9.
8. Knight, E. L., Stampfer, M. J., Hankinson, S. E., Spiegelman, D., & Curhan, G. C. (2003). The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Annals of internal medicine, 138(6), 460-467.
9. Bedford, J. L., & Barr, S. I. (2005). Diets and selected lifestyle practices of self-defined adult vegetarians from a population-based sample suggest they are more'health conscious'. International Journal of Behavioral Nutrition and Physical Activity, 2(1), 1-11.
10. Blum, M., Averbuch, M., Wolman, Y., & Aviram, A. (1989). Protein intake and kidney function in humans: its effect on'normal aging'. Archives of internal medicine, 149(1), 211-212.
11. Dawson-Hughes, B., Harris, S. S., Rasmussen, H., Song, L., & Dallal, G. E. (2004). Effect of dietary protein supplements on calcium excretion in healthy older men and women. The Journal of Clinical Endocrinology & Metabolism, 89(3), 1169-1173.
12. Potgieter, S. (2013). Sport nutrition: A review of the latest guidelines for exercise and sport nutrition from the American College of Sport Nutrition, the International Olympic Committee and the International Society for Sports Nutrition. South African journal of clinical nutrition, 26(1), 6-16.
13. Kimball, S. R., & Jefferson, L. S. (2006). Signaling pathways and molecular mechanisms through which branched-chain amino acids mediate translational control of protein synthesis. The Journal of nutrition, 136(1), 227S-231S.
14. Gibala, M. J. (2007). Protein metabolism and endurance exercise. Sports Medicine, 37(4), 337-340.
15. Wolfe, R. R. (2017). Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?. Journal of the International Society of Sports Nutrition, 14(1), 1-7.
An article by tutor: George Pollitt.