This paper reviews the recent literature concerning the importance of the gut in extraintestinal protein metabolism. A growing body of evidence suggests that the gut modulates amino acid flux and inter-organ relationships in various metabolic states. This may be particularly true during the absorptive period, when the gut: (1) controls amino acid absorption; (2) may modulate catabolism and uptake for synthesis of absorbed amino acid; and (3) consequently influences the availability of liver and extrasplanchnic amino acids, as well as their pattern and kinetics through portal flow delivery.