askchapo

Minor CW: disordered eating, drugs, animal experimentation.

Seems like a lot of folks have responded while I was away, and my last couple hours of research tends to agree with them. Seems like my initial knee-jerk skepticism might have kicked in a little hard in this case. I'm pretty drained from work so this is probably going to be a half-assed kind of effortpost, but here we go anyway, because getting deep in the weeds about food and diet is kinda what I do.

All other things being equal, being a healthy weight is going to be better for you than not (this goes for over and underweight), regardless of what specific method you use to maintain your energy balance. That is, provided you're not doing anything extreme (e.g. keto, binging / purging, meth). So, in that sense, if you can maintain a healthy weight doing intermittent fasting (IF), it's probably alright. Or at least, not bad.

It gets a bit more hairy when you get into the science. While the RCT quoted in the Skepchick article that someone posted upthread is good, RCTs are necessarily limited in scope. This particular one only compared 8-hour time-restricted eating (TRE) to a calorie restricted diet over 12 months, and for weight loss only. They performed about the same. There are several meta-analyses (aggregate analysis of other RCTs) that generally agree; most forms of IF do about the same as continuous energy restriction (CER -- ie low-calorie) diets in terms of weight, fat and cholesterol over a long enough timeline. However it's worth noting that IF only works if you -actually- reduce calories overall. Fasting does nothing if your weekly calorie intake stays the same (eg- binging on high calorie foods on your "feast" days).

Additionally, there are different forms of IF. This umbrella review of meta-analyses focused on four kinds; Zero-calorie alternate day fasting (ADF) ie- eating only every other day, modified ADF (restricting calorie intake every other day), 5:2 (five days eating, two days fasting at various calorie intake levels), and TRE, as explained above. It does highlight a few places where specific kinds of IF MIGHT outperform CER for certain outcomes (5:2 diet for fasting insulin, for example) or in certain situations (MADF might be better for obesity). But this is really dietician territory, and I'm not a dietician. If you have a specific problem beyond wanting to be a healthy weight, you need to talk to one. Incidentally, this might be where some of the woo around it comes from; there is some preliminary work in animal models and theoretical pathways suggesting it might have some benefit alongside chemotherapy. This is really cutting-edge theoretical stuff, and I'm not an oncologist, either. It's a big deal if it's true, but nobody is sure yet. OTOH, being a healthy weight definitely reduces your risk by a good margin. If fasting is what gets you there, cool. Just don't neglect actual medical treatment if you need it.

Other folks have also mentioned the risk of it evolving into disordered eating. There are survey studies that seem to suggest a correlation, but that's also somewhat true of -any- kind of dieting. This also doesn't really establish causality; ie- are they exhibiting disordered eating because of IF, or are they using IF to mask disordered eating, or is there a common thread where people who tend toward disordered eating anyway might find IF more attractive? Regardless, if you feel like you might be vulnerable to that kind of thing, maybe steer clear for now and talk to your doctor and/or psych about it. I'm not a psych, either, btw.

Lastly, maintanence. There doesn't seem to be a ton of data on this, and what data there is suggests it's about the same as CER. Which is a shame, because generally speaking, losing weight isn't as hard as keeping it off. I imagine it might be easier to integrate a time-based regimen into your lifestyle than a calorie-based one, since you don't have to count anything other than hours. That's kind of speculation on my part, but some of the other anecdotes in-thread make an intuitive kind of sense to me.

Overall, seems like it's probably not much better (or worse) than any other method of calorie control for weight loss. Any health benefits are more likely due to weight loss rather than anything specific about the diet though. Advice about eating disorders is valid, and Your Mileage May Vary. The best diet is the one that works for you.