The whey proteins are rich sources of leucine and affect mTOR-mediated skeletal muscle protein synthesis. The present authors wished to investigate the dose–response effect of chronic supplementation of the whey proteins (WP) with leucine on the anabolic pathway proteins mTOR and p70S6K in the diaphragm of sedentary and exercised Wistar rats. Ninety-six weanling male Wistar rats were divided into eight groups and fed for 30 day diets containing either casein or WP, with increasing levels (0, 3, 4.5 and 6% of the diet) of leucine. A parallel set of eight groups was exercised for comparison. Serum uric acid, creatinine, glucose, AST, ALT, CK, LDH and cholesterol, were determined by standard methods, and mTOR and p70S6K, using the Western blot analysis. Leucine supplementation increased both, mTOR and p70S6K in the diaphragm in a dose-dependent way, independent of the type of dietary protein. These changes produced no significant increase in either diaphragm or protein mass Ver menos