Dietary protein requirements in athletes

Abstract

Current dietary protein requirements were determined using essentially sedentary individuals and, therefore, are designed for the general population. Unfortunately, the recommendations from these studies have been applied to athletes as well. Because of the vast differences in daily energy expenditure alone this would seem to be a naive approach. Moreover in recent years, considerable evidence has accumulated on athletes, primarily those involved at each end of the exercise intensity-duration continuum, i.e., strength (weight lifting) to endurance (running, cycling, or swimming), suggesting that dietary protein needs may be greater by as much as 125% in comparison to sedentary individuals. The additional protein may be necessary for use as an auxiliary fuel for endurance exercise and as a supplementary source of amino acids to build and/or maintain the large muscle mass present in those who strength train. In addition, although more speculative, it is possible that other constituents in high quality protein sources, i.e., creatine, conjugated linoleic acid, carnosine, etc. may also be beneficial. Definitive dietary recommendations for various athletic populations must await further study, but the mass of current evidence indicates that individuals involved in strength/power/speed activities may benefit from intakes of about 1.7 to 1.8 g protein·g body mass-1·day-1 (approximately 112-125% higher than the sedentary recommendation) and those who participate in endurance activities from about 1.2-1.4 g·kg-1·d-1 (approximately 50 to 75% higher than the sedentary recommendation). Assuming total energy intake is sufficient to cover expenditure, these intakes can be obtained from a diet consisting of about 10% energy intake as protein. Some athletes may not consume this amount of protein, especially those who consume inadequate energy (dieters or those trying to maintain an arbitrary body mass for their activity, i.e., gymnasts, dancers, wrestlers, etc.), those who are growing (children, adolescents, women who are pregnant), or those who select diets which may exclude high quality protein sources (vegetarians and seniors). Despite the common practice of consuming greater amounts of protein (2-4 g·kg-1·d-1) among strength athletes in particular, few data exist suggesting that this has any further benefit, i.e., there appears to be a ceiling effect. Finally, the concerns expressed routinely about liver or kidney problems with high protein diets have little scientific support; however, the easy accessibility of individual amino acid supplements poses a potentially serious threat because there are likely a variety of confounding interactions and the effects of mega doses of single amino acids are largely untested. Future studies are needed to fine tune these recommendations.