Amino acid prevents muscle breakdown

A study published in the December 2005 issue of The Journal of Physiology reported the findings of researchers at the Human Nutrition Research Centre Clermont-Ferrand and Institut National de la Recherche Agronomique in France that adding the amino acid leucine to older individuals' diets could help prevent the muscle breakdown that occurs with aging. After age 40, humans lose 0.5 to 2 percent of their muscle tissue per year.

In the current research, Lydie Combaret and colleagues studied muscle breakdown in young and old rats. Immediately after amino acids are consumed, muscle protein degradation slows and protein synthesis increases. This process is less effective in older animals, resulting in increased breakdown and slower synthesis. While it had been demonstrated that leucine could improve protein synthesis, the amino acid's effect on breakdown had not been previously determined.

They found that the slow in degradation following a meal did not occur in the older rats, but adding leucine to the diet restored breakdown in older animals to that of younger rats. The authors believe that the problem results from a defect in the machinery that breaks down contractile muscle protein. Senior co-author Didier Attaix commented, "Preventing muscle wasting is a major socio-economic and public health issue, that we may be able to combat with a leucine-rich diet."

In an accompanying "Perspectives" article in the same issue of the journal, Michael J Rennie summarized, "When old rats are fed a diet which is supplemented with leucine, there is what amounts to a rejuvenation of the normal postprandial inhibition of muscle protein breakdown . . . This is exciting because it strengthens the idea of a co-ordinated linkage between the meal-related stimulation of protein synthesis and the inhibition of breakdown."