OK, I love these kind of discussions. I just went to PubMed and found this article that totes the aspect of leucine supplementation.http://www.ncbi.nlm.nih.gov/pubmed/24327520Leucine improves protein nutritional status and regulates hepatic lipid metabolism in calorie-restricted rats.
Pedroso JA1, Nishimura LS, de Matos-Neto EM, Donato J Jr, Tirapegui J.
After taking an embryology class and finding out how different we are from rats/mice/rodents, I do not take it too seriously about the outcome of obese rats going on a caloric restriction diet and preserving muscle mass during their large weight loss.
And so they make a generalized statement:
"These results indicate that increased leucine intake may be useful in preventing excessive protein waste in conditions of large weight loss".
?Can this be comparable to a human who exercises alot (assumed not obese), is going from a diet focused on muscle mass gains to a diet to get the bodyfat down (manipulating nutritional macros), all the while preserving the hard earned muscle mass??
IMO: you really need to look at the details of the experiment to get at the truth of the hypothesis, and at what perspective is the answer coming from.
mTor is such a big buzzword in the research field. I glanced over the two papers, and saw nothing specific on connecting leucine with ageing. There are too many other factors to consider to make such a broad generalized statement.