In this interview, Leonie Heilbronn, Ph.D., discusses an ongoing 18‑month clinical trial involving 210 participants with obesity that compares intermittent fasting (IF) to continuous calorie restriction (CR). The study consists of a six‑month intensive phase with frequent monitoring and support, followed by a 12‑month follow‑up where participants continue the assigned diet with minimal assistance. The trial is fully blinded; no interim analyses have been performed, and results are not expected until after the final follow‑up in November 2021, with publication likely in 2022. The interviewee expresses expectations based on prior observations: CR participants often regain weight (citing the “Biggest Loser” phenomenon and ghrelin signaling), whereas IF may mitigate weight regain for some individuals. However, existing large‑scale studies with 12‑month follow‑ups have shown no significant difference between IF and CR overall, suggesting that benefits may be individual‑specific. The conversation also highlights the randomization process, which prevents participants from choosing the diet they feel suits them, and notes that some people adapt well to fasting while others experience irritability and difficulty habituating.
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One of the other studies that I'm super excited to hear about, you're looking at 210 people with obesity comparing intermittent fasting and restricting calories. How far along is that study? Because I, I'm really hopeful to see the results, but.
Can you share? Yeah. So the Last patient finishes November 21st. So it's, it's, it's an 18 month trial. So we do a six month really active phase where we see them a lot and we help them out and that phase is over. And then they have a 12 month follow up after that period where we really let them go and say, we say try to continue doing this diet without our help and we bring them back 12 months later to see how they're going. So that phase does not finish until November 2021. So probably not till 2022 will we have the study out. So, so they take a long time. But I'm excited by this.
So early results that are not, you know, statistically valid and all. Does one seem to work better than the other or you just have no clue yet?
We really don't have a clue yet. We have, you know, statisticians on this trial that blind everything and yeah, we, we don't, we don't have a handle on that at all unfortunately. We have done no, you know, no analysis on anything. So we have to wait till the end of the trial.
You're super blinded then. Well, kudos to you for doing, doing good science. And I'm sad because I'm pretty sure that what you're going to see, especially with a one year follow up like that is the people who do calorie restriction gain all their weight back. Because all you have to do is watch the Biggest Loser and just go a year out from everyone who loses weight on that show and they're all fatter than they were in my own life. You know, I lose 20 pounds, gain 30, lose 30, gain 40. Most likely because of ghrelin signaling. But then you do fasting or do anything with ketones, it seems like it becomes a non issue. So I'm, I'm very excited to see those results.
I'm hopeful too, but I don't know. So there's only one real trial or maybe is there two now that have done this in large populations and they've shown that there wasn't any difference either between the calorie restriction and intermittent fasting groups. They've done 12 month follow up, not 18 month follow up, but interesting. Yeah, they didn't see any difference between the chiral restriction and intermittent fasting group So I think that intermittent fasting really works for some individuals but it doesn't, it doesn't perhaps work for all individuals. So there's, there's that you know we don't let them choose when they do these research studies they get randomized into fasting or caloric restriction and they don't get to say okay I think that I'd suit fasting better or I'd suit calorie restriction better and I think that, that some people and I'm one of them I prefer fasting and being able to eat what I like on the weekends sort of thing and then you know go hard during the week and yeah so I think that some people really suit it and then some people get really grumpy during the fasting period and they just from what I've seen don't, don't habituate. So some people takes them a little while to get used to fasting and then some people just maybe never get used to it sa.
