High protein diets are beneficial to weight loss. The exact reason for this is not clear but may relate to the availability of protein to build skeletal muscle. As skeletal muscle tissue increases in mass, body composition improves because the percentage of total body mass contributed by fat tissue decreases. In addition, skeletal muscle is highly metabolic active and the resting metabolic rate of an individual correlates directly to the amount of skeletal muscle they possess. Further, skeletal muscle has an insulin and blood glucose lowering effect because movement and exercise increases the sensitivity of muscle to insulin, and the more skeletal muscle present, the larger the capacity to act as a conduit for blood glucose. Therefore it is recommended that those that wish to lose weight should consume a reasonably high intake of protein and perform some exercise that builds skeletal muscle. This combination has been shown to increase skeletal muscle mass significantly in just a few weeks of following the protocol.
Leucine has muscle building effects. Leucine is an amino acid found in protein foods, and it is one of the branched chain amino acids. Supplementation with leucine has been shown to increase skeletal muscle growth in the elderly, irrespective of protein intake and irrespective of resistance training participation. As skeletal muscle mass is inversely associated with mortality, especially in the elderly, leucine supplements may provide significant health benefits to the elderly. Leucine may also have fat loss effects because skeletal muscle mass is directly correlated with resting metabolic rate. Consuming high protein diets are one way to increase leucine in the diet without taking supplements. However, leucine supplement may be a more effective way of achieving the high intakes of leucine necessary to stimulate muscle growth. Whey protein contains high amounts of branched chain amino acids, including leucine.
Protein contains amino acids, and one group of amino acids that have muscle building effects are the branched chain amino acids. The branched chain amino acids include isoleucine, leucine and valine. Of these leucine has been shown to have anti-catabolic effect in skeletal muscle, and this may explain the muscle building effects of high protein diets. Leucine ingestion has been shown to stimulate muscle growth, and this has been demonstrated in individuals of different ages. For example, in one study, researcher administered 5 grams of leucine to elderly subjects (65-85 year) with high or low protein diets. The administration of leucine increased plasma leucine levels, and stimulated protein synthesis irrespective of the protein content of the diet. Further leucine stimulate protein synthesis in subjects who performed resistance training, and those who did not. Combined with other data, this study strongly suggests that leucine, and not total protein intake, is the main determinant of skeletal muscle growth.
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