There is a growing interest in the role of microbial populations of the gut in aging and health, with evidence from recent years suggesting that their level of influence might approach that of exercise. Some fraction of the benefits to health and longevity that occur due to the practice of either calorie restriction or intermittent fasting are thought to be mediated by resulting changes in gut microbe populations. This seems a safe assumption, given the evidence to hand, but the still open question is just how large or small that fraction might be. The consensus view remains that benefits largely result from increased cellular housekeeping, and the fact that calorie restriction fails to work in animals with disabled autophagy is telling.
Complicating the matter, however, calorie restriction and intermittent fasting are not just two ways of achieving exactly the same result. They produce significantly different patterns of gene expression in animal studies. Intermittent fasting without reducing calorie intake still produces health and longevity benefits in rodents. Calorie restriction lasting for less than three days in humans fails to produce the significant benefits to immune cell populations that fasting
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