Intermittent Fasting is trendy now, especially for weight loss. Its lesser known sister is Calorie Restriction, on which it’s partly based, although they aren’t the same. But both are getting a lot of attention in the scientific sphere, with studies promoted mainly by organizations with a focus on longevity, such as the National Institute of Aging.
I’ve been reading many of these publications, which you can easily find at PubMed by searching “intermittent fasting” or “calorie restriction”. Also articles more oriented towards popular science. And, although the results seem revolutionary at first sight… when you look at them with a cool head you discover many holes and questions. Those are what I’m going to talk about for the next two posts.
I don’t intend to do here a revision of the studies, but to bring up a series of considerations when it comes to interpreting them. To throw out some questions to ask yourself to analyze them critically.
Intermittent Fasting (IF) or Calorie Restriction (CR)?
I see that, in many publications about IF, when they go beyond the average people level of weight loss method, they associate it to something called calorie restriction. This concept shouldn’t be mistaken for calorie deficit, which just means eating less calories than you burn in order to lose weight.
CR implies living constantly with less calories than our body needs, although its followers would say that what happens is that the recommended amounts are too high and you can live with much less. They believe that, following a diet as restrictive as possible, they’ll be able to extend their lifespan. Even at the cost of their mental health or even, paradoxically, physical, as we shall see.
On the basis of this, there are people who defend IF as a way of “tricking” the body, so they can achieve the same benefits for longevity that CR promises, but without having to actually reduce the total amount of calories they eat; they just have to distribute them in a way that makes them spend more time without eating. Their theory is that, since autophagy —regeneration of cells— occurs when you don’t eat, the more time you don’t eat, the more this process is boosted and that’s the secret to eternal youth.
But think about this
Truth is, we all practice IF. We aren’t eating all the time, we fast between meals. The longest fasting period is the one that goes from your last meal of one day to your first meal of the next, which hopefully lasts at least 8 hours, preferably 10 (it seems to be better not to eat just before going to bed). During those times, our body carries out autophagy. But they think that’s not enough; however, they can’t agree on how it would be enough. There are several ways to practice IF, from fasting completely for 1 or several days a week to eating every day, but only at certain hours.