Dietary protein for athletes: from requirements to metabolic advantage.

The Dietary Reference Intakes (DRI) specify that the requirement for dietary protein for all individuals aged 19 y and older is 0.8 g protein.kg-1.d-1. This Recommended Dietary Allowance (RDA) is cited as adequate for all persons. This amount of protein would be considered by many athletes as the amount to be consumed in a single meal, particularly for strength-training athletes. There does exist, however, published data to suggest that individuals habitually performing resistance and (or) endurance exercise require more protein than their sedentary counterparts. The RDA values for protein are clearly set at "...the level of protein judged to be adequate... to meet the known nutrient needs for practically all healthy people...". The RDA covers protein losses with margins for inter-individual variability and protein quality; the notion of consumption of excess protein above these levels to cover increased needs owing to physical activity is not, however, given any credence. Notwithstanding, diet programs (i.e., energy restriction) espousing the virtue of high protein enjoy continued popularity. A number of well-controlled studies are now published in which "higher" protein diets have been shown to be effective in promoting weight reduction, particularly fat loss. The term "higher" refers to a diet that has people consuming more than the general populations' average intake of approximately 15% of energy from protein, e.g., as much as 30%-35%, which is within an Acceptable Macronutrient Distribution Range (AMDR) as laid out in the DRIs. Of relevance to athletes and those in clinical practice is the fact that higher protein diets have quite consistently been shown to result in greater weight loss, greater fat loss, and preservation of lean mass as compared with "lower" protein diets. A framework for understanding dietary protein intake within the context of weight loss and athletic performance is laid out.