Intermittent Fasting With or Without Calorie Restriction?

While wandering the internet today, my attention was drawn to a post on intermittent fasting (IF) and its relationship to calorie restriction (CR), a topic I've touched on in the past. The author examines a brace of research papers and concludes:

In summary, it looks like intermittent fasting extends lifespan in rats and mice only when it is accompanied by calorie restriction. It does not mean that the animals are also put on CR; rather, they just naturally end up eating less (unlike humans, who tend to be very flexible and good at compensating for calories). And, in the rare cases that the animals actually do eat twice as much the next day, their lifespans are not increased.

I'm not sure I agree with the comment on eating habits for either humans or mice. Anecdotally, it seems that you'd have to work pretty hard at eating to catch up on the calories missed by practicing alternate day fasting. It's not something that will just happen if you're eating ad libitum. But I'm not polling a large sample size with that question. Perhaps most people easily manage to eat two day's worth of calories in a day.

In the broader context of intermittent fasting, and as the author of the post above does point out, IF without CR in fact extends life span in nematode worms, a process which seems to happen through molecular mechanisms separate from those known to be associated with CR. In addition, IF without CR produces other health benefits in mice:

We report that when [mice] are maintained on an intermittent fasting (alternate-day fasting) dietary-restriction regimen their overall food intake is not decreased and their body weight is maintained. Nevertheless, intermittent fasting resulted in beneficial effects that met or exceeded those of caloric restriction including reduced serum glucose and insulin levels and increased resistance of neurons in the brain to excitotoxic stress. Intermittent fasting therefore has beneficial effects on glucose regulation and neuronal resistance to injury in these mice that are independent of caloric intake.

Notice that those mice were capable of taking up the slack to consume twice as much on the eating days. It seems to vary from study to study as to whether animals will make up the difference.

The bottom line to all this remains much the same for now:

Both calorie restriction and intermittent fasting [can] produce significant health and longevity benefits in shorter-lived mammals such as mice, and at least significant health benefits in primates, including humans.

Far more research has been accomplished for calorie restriction, and uncertainty remains as to whether intermittent fasting is as good, definitely increases longevity, has a preferred method of practice, or whether it could even be harmful to long-term health if done incorrectly.

It seems plausible that calorie restriction and intermittent fasting produce their benefits in similar but different ways, based on research in lower animals, but I know of no research confirming this in mammals.


I agree that it would be pretty hard to practice intermittent fasting without producing caloric restriction. Fasting typically causes your appetite to be suppressed.

Not only does the literature point to the health benefits of both intermittent fasting and caloric restriction, I can attest to the fact that it results in more energy and a general feeling of well being. I love this expression "Nothing tastes as good as thin feels". Remember this next time you reach for something that is fattening and has no nutritional value.

Posted by: Brenda Rusnak - Longevity at June 2nd, 2010 4:39 PM

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