l-Leucine, an isoleucine antagonist in the rat

An excess of dietary l-leucine has been shown to retard the growth of rats fed low-protein diets or diets deficient in isoleucine. The addition of isoleucine to such diets overcame, to a large extent, the growth-retarding action of an excess of l-leucine. These observations suggest that an excess of dietary l-leucine can act as an antimetabolite of isoleucine in the rat and can thereby increase the requirement of the rat for isoleucine.