By Jimmy Downs

Sunday Sept 30, 2012 (foodconsumer.org) -- Rajavel Elango at The Hospital for Sick Children in Toronto, Canada and colleagues have published a study recently in the American Journal of Clinical Nutrition suggesting that the tolerance upper intake level (UL) for leucine, an important branched chain amino acid, should be 500 mg/kg/day or about 35 g/day for healthy adult men.

Leucine, a popular dietary supplement, has been believed to improve athletic performance and is commonly used along with other branched chain amino acids isoleucine and valine by bodybuilders to build muscle. Studies showed supplements of these three branched chain amino acids can help people on a protein-restricted diet to prevent muscle loss among other things.  But the tolerable upper intake level for leucine is unknown.

The researchers tested different doses of leucine in five healthy adults and measured plasma and urinary biochemical parameters and changes in leucine oxidation to determine what dose would be adequate for healthy adult men.

They concluded "On the basis of plasma and urinary variables, the UL for leucine in healthy adult men can be suggested at 500 mg · kg−1 · d−1 or ∼35 g/d as a cautious estimate under acute dietary conditions."