Protein intake and muscle mass.

There is a general belief among strength-trained athletes that high-protein intakes have a positive effect on muscle mass accretion and lead to greater strength gains. There is now substantive evidence indicating that protein intakes above the current recommended dietary allowance (0.8 g . kg(-1). day(-1)) are needed to maintain positive nitrogen balance. Restricted energy intake in an attempt to reduce body weight to make a particular weight class, results in increase in protein needs. For strength athletes, protein intakes of 1.6 to 2 g . kg(-1). day(-1) are close to the optimal requirements for muscle development. There is now experimental evidence that excessive protein intake compared with adequate intake does not result in an increased muscle protein synthesis. Amino acids deriving from excess protein intake are oxidized rather than stored as protein. Thus, there is no data available to dare, showing that protein intakes as high as 3-4 g . kg(-1). day(-1) have positive effects on muscle mass development. Gains in muscle mass are likely influenced not only by the volume and intensity of exercise during training, but also by the hormonal environment of the muscles. It has been hypothesized that amino acid supplements call influence the hormonal milieu during and after strength exercise and promote skeletal muscle anabolism. There is only little scientific evidence supporting the hypothesis that specific amino acid supplements may stimulate growth hormone (GH) release. It is likely that the magnitude of GH production consequent to heavy-resistance exercise might be higher than GH release resulting from amino acid intake. However, carbohydrate-protein supplements can affect the anabolic hormonal milieu after exercise, and are able to stimulate an environment favorable for muscle growth by increasing plasma concentrations of GH and insulin. Thus, while it is important to maintain protein balance during strength training, amino acids consumed in excess do nor result in an increased accretion of lean body mass.