Skepticism

Study: Can You Fast Your Way to Good Health? (Maybe!)

As you may know, every month I do a live “ask me anything” stream for my patrons, and last month one patron asked me to look into the research on intermittent fasting. I did, and I found the subject really interesting, and I said that I’d consider doing a public video on it if a new, really interesting study on it happened to pop up. Because you know, I like to keep things topical here on main.

And what do you know, a new, really interesting study has popped up, so let’s go!

Possibly obvious content warning for today’s video: I’m going to be talking about weight loss, calories, and general health stuff, so if that topic is no good for you, I recommend giving this one a skip! If you’re not sure, I’ll give you the “too upsetting, didn’t watch” summary right here at the top: if your goal is to lose weight but you can’t or don’t want to purposely restrict the amount you eat, restricting the hours in which you eat MAY be a successful strategy for you. However, there’s not enough evidence that intermittent fasting has any benefit beyond weight loss.

Before I get into it, first I need to say that I’m not a doctor, I’m certainly not YOUR doctor, and you should talk to your doctor before you make any drastic life changes for your health. Second, I do feel the need to acknowledge that a lot of people in my progressive audience think that weight loss is never good, that it’s always capitulating to a misogynistic male gaze audience, and that it’s not really about health and wellbeing. I don’t agree with that but I respect that every person can make their own decisions about their own body and their own health. As I’ve alluded to in past videos on this topic, I was diagnosed with degenerative disc disease when I was about 15 years old, and I’ve spent time completely incapacitated by it. Over the past 25 years I’ve learned that if I want to remain mobile and happy I need to keep my weight down to reduce the overall strain on my back, while also keeping my core as strong as possible.

So yeah, there have been several times in my life when I have focused on calorie counting. Weight loss can seem really complicated but for most people, it truly is a case of taking in fewer calories than you burn. When I track my calories, my weight loss adheres almost exactly to the general rule of one pound of weight loss for every 3500 calories under my maintenance. It’s simple, but it’s not easy. It’s hard because food is delicious.

But ultimately I get a weird sense of enjoyment from it: paying attention to everything I eat, tracking it, seeing the results, I find it kind of satisfying. But there are a lot of people who find it overwhelming, simply because the act of paying attention to everything they eat and counting the calories can become obsessive. Many people assign moral value to their food, and start to feel like failures if they eat more than they planned, or they may eat way too little in order to speed up the process, leaving them without adequate daily nutrition and increasing their chances of giving up and overeating later.

Enter intermittent fasting. This is the idea of only eating or drinking calories within a certain window of time: for some people that’s 12 hours (like between 8am and 8pm), and for others it’s within 8 hours (like between noon and 8pm). IF has been the subject of quite a lot of research over the past decade or two, and recently it’s become a pretty hot trend these days, which means that there’s a lot of misinformation and wild claims based on small, inconclusive studies.

There are two categories of claims for IF: weight loss, and everything else. So first let’s talk about weight loss, because that’s what the latest study is about. Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population was published this week in Annals of Internal Medicine, and I’m pleased to report it’s a randomized controlled trial, which is of course the ol’ “gold standard” for studies like this. It means they compared three different groups that totaled 90 obese people: 30 who restricted their eating to a 8-hour window (noon to 8pm) but who didn’t count their calories, 30 who ate whenever they wanted but counted their calories, and a control group of 30 who just kept on doing what they wanted without any restriction. They followed them for an entire year, and found that while the control group didn’t lose any weight, the other two groups lost about the same amount: 10 to 12 pounds.

The IF group ended up “naturally” reducing their calorie intake to about the same as the group that was purposely counting calories, probably because they weren’t doing late night snacking or drinking anymore. The fast was moderate enough that they cut out about 400 calories, which they tended to not OVEReat when the fast ended the next day. That’s great news for people who can’t or don’t want to deal with the annoyance of counting calories.

There IS a “but,” though: both the IF and the calorie counting groups got guidance from dieticians who educated them on healthy food choices and cognitive behavioral training, which the average person doesn’t have and so we can’t say whether it’ll work in “the real world.” So if you try IF and you’re not seeing results, you might want to talk to a doctor, a therapist, or a dietician who can help you learn better strategies.

So that’s the news on weight loss: it MAY work for you if you don’t overeat post-fast.

But as I mentioned, there are a LOT of other claims made by people promoting IF: slow down aging, reduce inflammation, lower blood sugar, avoid cardiovascular disease, cure your depression, develop telepathic powers, etc. etc. These are almost all based on the idea that there’s some benefit to putting the body under a controlled amount of stress, and by “stress” I mean it in the same way exercise is good for us because it puts our body under stress. And there might be something to some of these claims: researchers have found some evidence for it in rodents. When it comes to people, it’s a lot less convincing: Cochrane did a systematic review and found evidence lacking for changes in blood sugar and cardiovascular disease.

Another systematic review published in 2021 found that people who fasted had lower rates of anxiety and depression, but that the evidence is pretty weak. The conclusion is what I keep seeing over and over for every benefit of intermittent fasting: it’s safe to try it, meaning that people who don’t have disorders like diabetes are generally fine to fast and that they don’t tend to starve themselves or develop eating disorders, and maybe it’ll help but there’s no clear evidence yet. 

There are a lot of people online who are trying to figure out how to maximize their results: will only eating in the morning be better than the evening? Some research suggests that that’s true. Is a 16-hour fast better than a 12-hour fast? Some research suggests that that’s true. But the reality is that there just isn’t enough data to say for sure. Like, if the jury’s still out on if fasting makes a significant difference on all these markers at ALL, there’s no way we can stay which TYPE of fasting is better than another.

This is one of those areas that I personally find really interesting because it seems to be something where you yourself can do a little science experiment ON yourself. If your doctor is okay with it and you’re curious how it might affect you, give IF a go! Pick the 8-hour window you prefer and restrict your eating to those times, and see what happens. Do you have more energy? Less anxiety? Fewer aches and pains? Maybe it’s the placebo effect but who cares if you end up feeling better? And if you end up not enjoying it, well, no harm.

Just don’t get weird about it. By which I mean, don’t get obsessive, don’t turn it into a disorder, and don’t even turn it into your personality. Don’t bring it up at parties. Definitely don’t go writing a book about how eating between 8am and 4pm gave you magical powers. We don’t need any more Gwyneth Paltrows for god’s sake.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor. Twitter @rebeccawatson Mastodon mstdn.social/@rebeccawatson Instagram @actuallyrebeccawatson TikTok @actuallyrebeccawatson YouTube @rebeccawatson BlueSky @rebeccawatson.bsky.social

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