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Getting older? Extra leucine boosts anabolic stimulus of proteins

A couple of grams of leucine [chemical structure below] boosts the growth stimulus that protein-rich meals provide to muscle tissue. At least, in elderly people, according to American scientists in the American Journal of Physiology, Endocrinology & Metabolism.

Leucine is more than an essential amino acid that your body needs to build up muscle tissue. Research has shown that it also has a signalling function. Meals or supplements containing high amounts of leucine increase the production of insulin and stimulate the molecular machinery that muscle cells use to build up muscle fibre.

If you add leucine to a protein-rich meal, elderly people build up more muscle protein as a result, French researchers reported three years ago. Good news for older strength athletes.

When you're still below thirty your body reacts well to the anabolic stimulus of a protein-rich meal. As you get older, your sensitivity to the stimulus declines. Maybe older athletes can help stem the decline by concentrating their protein intake to a limited number of eating sessions during the day. This concept is called 'pulse feeding'. Proteins whose amino acids reach the blood quickly after intake, like whey proteins and soya proteins, are believed to be most suitable.

But how do young people react to extra leucine given with protein-rich meals? Researchers at the University of Texas went in search of the answer by doing an experiment on twenty men and women in their mid-sixties, and a similar number of men and women aged around thirty.

Half of the test subjects were given a mix of amino acids that approximated the composition of amino acids in whey protein, 26 percent of which consists of leucine.

The other half got a similar mixture, but then with proportionally more leucine: this mix consisted of 41 percent leucine. The researchers had reduced the amount of the other amino acids in the mix, so that both groups consumed 6.7 g of amino acids.

After the test subjects had consumed the amino acids, the researchers measured their fractional synthetic rate. This gives an indication of the amount of muscle tissue the test subjects' muscles were building up. The figure below shows the FSR during the first 210 minutes after consuming the amino acids.

Getting older? Extra leucine boosts anabolic stimulus of proteins

The 'ordinary' amino acid mix did not have a statistically significant effect on the production of muscle protein in the elderly subjects, but the leucine-rich mix did have a significant effect. For the young test subjects it made little difference whether they ate amino acids with 41 or 26 percent leucine.

The researchers also looked at the amount of the amino acid phenylalanine that the muscle tissue absorbed or released. The more phenylalanine that muscle cells absorb, the greater the building processes in the muscle and the less pronounced the breakdown processes.

Getting older? Extra leucine boosts anabolic stimulus of proteins

The leucine-rich amino acid mix strengthened the anabolic processes in the elderly - or weakened the catabolic processes. In the young people the leucine had no effect.

Leucine supplements are gaining some popularity in the supplements world. Strength athletes take a few grams of the [foul-tasting] stuff together with their protein-rich meals in the hope of making their bodies into a more anabolic environment. And judging by recent studies, it's not such a strange idea.

By the way, the research was funded by the Japanese company Ajinomoto, a leucine producer.

Am J Physiol Endocrinol Metab. 2006 Aug;291(2):E381-7.