The new study, published in the journal Nutrition (Vol. 22, pp. 520-527), used 28 Wistar rats eating the model AIN-93M diet for three weeks. The rats were subsequently divided into two groups, one continued to eat the normal diet, while the second group ate the diet plus a 0.6 per cent L-leucine supplement for a further six weeks.
"Significant decreases in the amount (minus 24.5 per cent) and percentage (minus 22.6 per cent) of body fat were observed for the leucine group compared with the control group," reported lead author Jose Donato, Jr. from the University of Sai Paulo.
No difference was observed however in the muscle mass of the rats, or in the mass of the vital organs.
Supplementation with the amino acid was also associated with an improvement in indicators of protein nutritional status.
"A higher protein synthesis rate might increase energy expenditure and this additional energy demand can be satisfied mainly by the oxidation of body fat," wrote Donato.
The researchers noted that leucine supplementation by itself may have side-effects, such as impairing the availability of other branched-chain amino acids (BCAA). However, "even if changes in the metabolism of other BCAAs had occurred, this was not sufficient to abolish the beneficial effects of supplementation itself on the variables analysed here," said Donato.
"The fact that even moderate doses of leucine have shown positive results is extremely relevant for the clinical application and extrapolation of these data to humans," concluded the researchers.
The demand for leucine and other amino acids is growing thanks to trends in the animal feed market but human nutritionists are becoming increasingly interested in amino acids and peptides for food use too.
Amino acids are already widely used in foods in Japan but with tryptophan supplements coming back on the UK market, and ingredients companies developing peptides for lowering blood pressure and other applications, amino acids like leucine may start to see increasing demand in Europe also.