Thursday, June 17, 2021

skepticism about intermittent fasting

Just seen on Instapundit: an article casting doubt on the benefits of intermittent fasting: "A Potential Downside of Intermittent Fasting: A rigorous three-month study found that people lost little weight, and much of that may have been from muscle." Here's an excerpt:

The new research, published in JAMA Internal Medicine, is one of the most rigorous studies to examine time-restricted eating, which involves fasting for 12 or more hours a day. Many followers of the diet, which has been popularized in best-selling diet books and touted by celebrities, routinely skip breakfast and eat all their meals between roughly noon and 8 p.m., resulting in a daily 16-hour fast.

Research over the years has suggested that the practice spurs weight loss and improves metabolic health, although much of the data has come from animal experiments or small studies of relatively short duration in humans. Experts say the diet works because it allows people the freedom to eat what they want so long as they do it in a narrow window of time, which leads them to consume fewer calories over all.

But the new research found that overweight adults who were assigned to routinely fast for 16 hours daily, eating all their meals between noon and 8 p.m., popularly known as the 16:8 diet, gained almost no benefit from it. Over the course of the three-month study, they lost an average of just two to three and a half pounds — only slightly more than a control group — and most of the weight they shed was not body fat but “lean mass,” which includes muscle.

Obviously, this is only one study, and there's a certain level of subjectivity when it comes to dieting, i.e., your mileage may vary. But as I said before, it's good to listen to the skeptical voices. This actually helps you to make more-informed choices. As to this article, I've actually heard this news before, that fasting can cause the body to cannibalize its own muscles. So this study is nothing new, but one should still be mindful that fasting comes with risks.

I should note, though, that the above excerpt is misleading when it says "eat what they want." You can't subsist on chocolate cake just because you're now on a 16:8 schedule. The nutrition you take in—and its quantity—is still vitally important if your goal is to lose weight. So the onus is still on you to both eat healthily and control your portions (that last part is what I've always found most difficult; I've spent most of my life as a big eater).


Charles said...

As you know, I am a dedicated intermittent faster, although my goal was never to lose weight. I've been doing IF for over half a year now, and my weight has stayed roughly the same. IF for me has always been about just being healthier in general.

As for fasting causing the body to cannibalize it's own muscles, I have actually seen an increase in my muscle mass (and a corresponding decline in body fat) since I began IF. Of course, I also try to eat healthy and exercise regularly, so I don't attribute that entirely to IF.

Honestly, I don't think any system is going to work if you're just going to treat it like a magic bullet and not put in any effort to change your habits. Like you said, it's not like suddenly restricting all of your eating to an eight-hour window is going to change much of anything if all you eat is chocolate cake. And if you don't throw exercise into the mix then, yeah, I could see people losing muscle mass.

Kevin Kim said...

Dr. Jason Fung's version of IF is the regime I'll be switching to when I'm done with my austerity. This will be a fairly intensive form of IF in which I follow an 18:6 schedule and don't eat for four days out of the week (maybe a clear soup on a fasting day). I'm not too worried about the muscle-mass issue; I suspect that, if you have enough protein in your diet and you're exercising, muscle loss won't be a factor. At least not a major one.

Daniel said...

I'm gonna go out on a limb here and say the 16:8 and 5:2 iterations of IF are probably not radical enough. Although the pandemic stalled my admittedly weak efforts, I lost around 9kg over a few months using OMAD IF (One Meal a Day), which in turn triggers autophagy and shuts down the mTOR pathway. Of course, you can also pop a couple of milligrams of rapamycin once a week (pulsed dosing) or a daily metformin pill to get roughly the same therapeutic outcome, but since weight loss is also important, dietary changes are the way to go. Rapamycin is also said to reset the body's epigenetic clock. Check out for more details. (I'm on 5mg once a week and definitely FEEL younger, but that could just as easily be the placebo talking.)

Kevin Kim said...


I'm on metformin already; I don't know whether you saw my belated reply to your comment from several days ago. I'd eventually like to get off all meds.