Leucine supplements could help prevent muscle loss
French researchers who have reported positive results on rats.
By supplementing the diet of young (8-month) and old (22-month) rats with 5 per cent leucine, the scientists from INRA's Human Nutrition Research Centre in Auvergne showed that muscle loss was repressed in the older rats.
The study also found that elevated levels of peptidase enzymes and proteasome subunits characteristic of old muscle were suppressed in 22-month old rats chronically fed a leucine-supplemented diet.
A natural balance exists in adults between muscle breakdown and buildup. After a meal muscle loss slows down and synthesis doubles. However, as we get older this balance is upset and muscle breakdown begins to dominate. Annual muscle loss for people over 40 can be as much as two per cent.
The researchers established that muscle loss does not slow down after feeding in older animals, so there is excessive loss.
"Thus the defective postprandial down-regulation of in vitro proteasome-dependent proteolysis [breakdown of contractile muscle-protein] in 22-month-old rats was restored in animals chronically fed a leucine-supplemented diet," wrote Lydie Combaret and colleagues in the December issue of the Journal of Physiology (vol 569, issue 2, pp 489-499).
A diet rich in protein, and therefore also leucine, has previously been shown to increase weight loss in highly active people. Professor Donald Layman from the University of Illinois, author of this earlier report, explained that "the diet works because the extra protein reduces muscle loss while the low-carbohydrate component gives you low insulin, allowing you to burn fat".
He also pointed out that the average American diet contains 4 or 5 grams of leucine, "but to get the metabolic effects we're seeing, you need 9 or 10 grams".
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.
