Oddbean

Also, you must not have read the article because the second paragraph describes subjecting them to regular fasting regimes, not lifelong caloric deficit. I don't believe lifelong caloric deficit is even possible nor is it mentioned in the article. Lastly, you can gain muscle and then maintain it on a caloric deficit anyways, it's what body builders do every season. So even your initial assertion is wrong. Now I know that is a little different, but you can build muscle and not gain weight too. I feel like you're way over simplifying the process of muscle gain and retention and the essence of this article is that obesity is bad

3-7 day fasts are known to stimulate stem cells to replicate and regenerate tissue... it is related to the process of ketosis, and apoptosis and autophagy (burning fats, cells committing suicide and cells consuming other cells)... something that i would mention is that all of these processes depend on adequate levels of iodine and not excessive levels of fluorine and bromine fasts are a good thing to do, at least a few times a year, i think, but the benefits of maintaining adequate levels of iodine can't be overstated... i had massive results with it and it affected my nerves and immune system in really good ways i was just made aware that it is a critical element in the chain that enables ketosis and without ketosis you don't really make good use of fats for energy, speaking of calories... i mean, combine raising iodine levels and after 3 days of fasting you will experience a massive metabolic boost that makes you able to tolerate cold a lot easier and increases endurance and strength

"Some mice were placed on calorie-limited diets, another group followed intermittent fasting regimens, and others were allowed to eat freely." Sounds like only some of the mice were fasted intermittently, others had calories restricted. I'm certainly open to the benefits of intermittent fasting and have experimented with it myself. Having practiced (natural) bodybuilding for years in the past I was never able to maintain muscle mass whilst restricting calories. This may just speak to my lack of talent as a bodybuilder. Pros are typically still using some sort of exogenous testosterone derivative while dieting for competition so I don't think that's a good example. As a competitive weightlifter in multiple weight classes for over 15 years I feel I have a good understanding of how my body reacts to various dietary interventions and in my experience anything but brief caloric restriction leads to loss of both fat and muscle (not to mention strength). BTW the Cambridge Dictionary's definition of frail seems to cover both our usages. https://m.primal.net/LRbC.jpg

The 1 day per week intermittent fasting group appears the most interesting to me as overall caloric intake was maintained but body weight slightly reduced (possible improvement in body composition?) and some measured health benefits. To me the loss of lean mass (and probable hunger) experienced by the 40% and 20% caloric restriction groups (if applicable to humans) would considerably reduce quality of life while increasing the risk of hospitalisation and early death from falling injuries in later life. Each to their own I suppose. My preference would be to live an averagely long life with a high capacity over a long life with compromised capacity.