It's been known for some time that muscle tends to waste away as we get older (over the age of 40, people start to lose up to 2% per year). A team of scientists at the INRAs Human Nutrition Research Centre in Auvergne has demonstrated that this loss - at least in rats - is prevented with sufficent Leucin supplementation.
So what is Leucin? Leucin is one of the essential amino acids (essential as the body needs it but doesn't produce it directly). As it's found in all protein foods, it isn't exactly difficult to come by. In fact, bodybuilders have been taking protein supplements with leucin for years. The study, however, focuses on the effects of muscle aging - and recommends, among other things, up to 9 or 10 grams per day (the average in the US is around 4 or 5) to reproduce the results shown.