People generally lose muscle as they age (sarcopenia). This can be the result of a few factors: 1) decrease in muscle fiber size, 2) conversion of fibers from type II to type I, and 3) decrease in the total number of muscle fibers.
Training can impact the first two of these variables, but the third, loss of muscle fibers was thought to be beyond control. Now some new studies are starting to question this belief.
This study(pdf) shows that in rats, calorie restriction led to no loss of muscle fibers with age. This held true whether the rats were younger or older when subjected to calorie restriction. The idea is that calorie restriction led to decreased oxidative damage and better protein turnover in the muscles.
This news item discusses a similar study where calorie restriction in rats led to virtually no loss in muscle function during aging.
I think all this is quite amazing given the traditional idea of sarcopenia. It's normally thought that muscles get weaker with age and that strength training is needed to counteract this. These studies suggest that diet may be a way to halt muscle loss as well.
The next question for me is that if calorie restriction works, will intermittent fasting have the same effects? In general, I believe that intermittent fasting provides all the benefits of calorie restriction without the costs (fatigue, loss of libido, etc.). I hope future studies will address this.
