Leucine and citrulline: two major regulators of protein turnover.

Both leucine and citrulline stimulate muscle protein synthesis, in part through a common mechanism of action mediated by the mTOR signaling pathway. Both leucine- and citrulline-enriched diets improve nutritional status in various experimental models of injury. However, in the context of intensive care unit (ICU) patients, there is conflicting data on leucine and no data at all on citrulline. Therefore, beyond a strong rationale, large clinical studies are required before any reliable recommendations can be issued on the use of leucine- or citrulline-enriched diets in ICU patients.