Intermittent Fasting Probably Isn't Making You Bald
Why recent headlines aren't as convincing as they might seem.
As with most fad diets, intermittent fasting is somewhat controversial. Proponents claim that it can extend your life and cure any manner of diseases, while opponents have raised fears that it could damage your organs in various ways. There’s also some concern that it’s just a hard thing to do, and so may not be the best dietary recommendation for most people to follow.
The latest news story about intermittent fasting seems to agree with the skeptical claims. Scientists have apparently shown that intermittent fasting may slow hair regrowth, potentially causing hair loss, which in turn could make adherents of the eating pattern go bald. For anyone trying intermittent fasting as a method of losing weight, that’s a pretty scary claim to hear.
As someone who lost most of their hair in their 20s, and also someone who has used intermittent fasting for a while to help manage my weight, I found these claims fascinating. Fortunately, while the headlines are very worrisome, the underlying data is not nearly as problematic as you might’ve heard.
Let’s dig into the science.
Shaving Mice
The new study that has everyone up in arms about intermittent fasting is a really interesting piece of research. There are two parts to this paper. The first is a lengthy series of investigations into mice. The authors took three groups of genetically identical mice, and after a lead-in period fed them either as much food as they wanted, only on alternate days, or only 8 hours out of every 24. This was meant to mimic different types of intermittent fasting strategies.
The series of studies is very complex, and I won’t go into all the detail here. If you’re interested in the cell mechanics of mice, and how various processes influenced hair cell growth when the rodents were fed these different patterns, I recommend reading the paper itself.
To briefly summarize the results, the authors showed that mice fed a ‘fasting’ pattern had slower hair growth when shaved than mice who were fed as much food as they wanted. The fasting mice didn’t have a lower caloric intake - on average, as determined by observing the amount of food eaten and comparing the groups using a statistical test - which was some indication that it wasn’t lower calories per se causing this issue.
There were a number of possible explanations that the authors explored for why these mice didn’t grow their hair back as quickly. They found that there was likely a fairly complex mechanism that involved the adrenal glands activating to prevent hair follicles from regrowing when mice were not eating for long periods of time. The study indicated that the process of burning through fat stores in these animals caused their bodies to slow the regrowth of hair by deactivating hair follicle cells, possibly to conserve energy.
This is all fascinating, but the next bit is perhaps the most interesting part of the study. The second part of the paper is only one short paragraph, but is rather remarkable - the authors conducted a randomized clinical trial comparing intermittent fasting with a more general low-calorie diet and a control group. They found that people who were doing intermittent fasting had about 18% lower hair regrowth than people not dieting at all, which they argued was evidence that the mechanisms they’d seen in mice were also present in human beings.
However, there are some holes to this theory.
Hairy Data
The first issue is one that I alluded to above. The paper tested all of these mechanisms in mice by giving one group all the food that they could eat and comparing that group to two groups who were given a diet that mimicked intermittent fasting. This is an issue, because they didn’t compare to any other type of diet. It’s not clear that the issues seen in this study are solely due to the fasting rather than having a lower caloric intake more broadly. There is some evidence that these changes were not due to lower calories, because the calories were not statistically significantly different between groups, but it’s still an important question to answer. This is particularly problematic because the authors don’t seem to have looked at how body weight interacted with the hair regrowth they were looking at.
It’s also an issue because the authors appear to have shown in their randomized trial of humans that this is exactly what happened. In the text of the study, they only talk about the intermittent fasting people compared to the control group. But they also had a group in this trial who were doing a regular low-calorie diet with no fasting.
If you look at the graph where the authors show the hair results in humans:
There is an effect of intermittent fasting. But there’s also an effect associated with general energy restriction. It’s hard to recreate the statistics here, but it looks almost certain that there’s no statistical differences between intermittent fasting and general dieting in humans.
Now, it’s also important to note that unlike the rodent research, the human trial was very low-quality. Of the 49 people that started the two-week trial, 23 dropped out. Because of this drop-out, there were substantial differences between the groups in terms of their characteristics - for example, the general diet group was 89% women compared to 63% in the intermittent fasting group and 33% in the control. This, along with the tiny sample size, impossibility of blinding diets, and all the other issues you commonly see in diet trials make the results all but meaningless regardless.
That being said, if we are to take the author’s primary contention about diets, it seems that this entire effect could be explained by the impact of eating less food. Certainly, the data in humans seems to support the idea. And while the data from rodents is intriguing, there’s a big difference between mice eating chow on a specific timer in a lab and humans eating diets in the real world.
Ultimately, what we’ve got here is a fascinating mechanistic investigation for mice that has little to no connection to dieting in real human beings. The fact that mice who are only fed on specific ‘fasting’ schedules have these enormous body changes is certainly interesting, but whether it relates to actual hair loss in humans is unclear.
It’s possible that intermittent fasting may make your hair grow a bit slower. It’s also possible that this could reduce the number of hair follicles you have. However, the data on this is mostly in mice so far, and the data we’ve got for humans seems to show that if anything it’s probably an issue for all diets rather than just intermittent fasting.
Personally, as a bald man who likes intermittent fasting, I’m not going to change my habits any time soon. Eating fewer calories if you’re a bit overweight is generally good for you in many ways. The benefits of weight loss far outweigh the worry about losing a few hairs.