The demands for amino acids in most organs and tissues do not
vary significantly from the fed to the postabsorptive state because
little surplus protein is accumulated. Furthermore, the hepatic
uptake of gluconeogenic amino acids decreases with nutrient
intake (5). Consequently, the primary fate of ingested amino
acids is incorporation into muscle protein to replete the reserves
of amino acids lost in the fasting state. Under normal conditions,
gains in muscle protein mass in the fed state balance the loss of
muscle protein mass in the postabsorptive state.