Lemon (1) wrote an overview on protein metabolism and the effects of physical activity on protein requirements. He reviewed existing research on protein intake for strength athletes and endurance athletes, as well as addressed the possible negative health concerns of high protein diets.
Lemon, P.W. Is Increased Dietary Protein Necessary or Beneficial for Individuals with a Physically Active Lifestyle? Nutr. Rev. 54(4):S169-S175. 1996.
FINDINGS: Overall, research on strength athletes suggests that an optimal intake of protein for building muscle mass is 1.7-1.8 g/kg of bodyweight per day. The optimal intake for endurance athletes appears to be 1.2-1.4 g/kg of bodyweight per day. These recommendations are significantly greater than the RDA of .8 g/kg and are only valid if caloric needs are being met. These recommendations are also based upon research on college-aged males consuming adequate energy intake. Protein requirements may be different for individuals on lower calorie diets, females, individuals of different age groups (such as elderly individuals, children or adolescents experiencing rapid growth, or pregnant women), and individuals less likely to consume an optimal mixture of nutrients (such as vegetarians).
The idea that high protein intakes can cause kidney problems appears to be a myth. This idea has been taken from research done on individuals with preexisting kidney disorders; however, such research cannot be extrapolated to healthy individuals. Numerous strength athletes consume diets extremely high in protein; if high protein diets caused kidney problems, one would see a much higher prevalence of kidney disorders in this population, which is not the case. In addition, animal studies utilizing very high protein intakes have not shown kidney problems. The increased nitrogen load placed upon the kidney by increased protein intake does not pose a potential threat to a healthy kidney.
When protein intake is high, water loss may be increased due to the excretion of additional nitrogen. Individuals must ensure that water intake is high to prevent dehydration.
The potential for high protein diets to increase calcium loss appears to be only a problem in purified protein. The high phosphate content of food protein negates any effect of protein on calcium.
IMPLICATIONS: Strength athletes should consume 1.7-1.8 g/kg body weight of protein a day, and endurance athletes should consume 1.2-1.4 g/kg body weight of protein a day, assuming that caloric needs are being met.
