In this interview, Dr. Krista Varady describes a controlled eight‑week trial that compared four groups of overweight women: (1) intermittent fasting with a 30% caloric restriction (fasting three days per week, eating ad libitum on non‑fast days), (2) continuous caloric restriction at 70% of normal intake, (3) intermittent fasting without caloric restriction (eating the same amount of calories as the restriction group but spread over the week), and (4) a control group receiving all foods without any restriction. All participants were provided all their meals. The fasting‑with‑restriction group lost slightly more weight than the continuous‑restriction group and showed greater improvements in diabetes‑risk markers and cardiovascular risk factors, exceeding expectations. However, because the weight loss differed, the study could not isolate whether benefits were due to fasting per se or simply greater weight loss. Adherence was high—over 50% of women enjoyed the protocol, likely influenced by media hype around intermittent fasting at the time. Participants reported reduced hunger on fasting days and did not overeat on re‑feeding days, suggesting possible appetite‑suppressing effects of fasting, perhaps mediated by ketones or ghrelin, though mechanisms remain speculative. The host shares a personal anecdote from the Bulletproof diet, noting that even when consuming very high calories (4,500 kcal) while fasting, he still lost weight, challenging the simple calories‑in‑vs‑calories‑out model, but cautions against intentional over‑feeding due to health risks.
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You do have a study in overweight women though, that you. You've done as well, right?
Yeah. On fasting. So yeah, we. This is the one where I was just mentioning before, where we fed them. This is the one where we fed them all of the foods. So we had four groups of women. We had women who were randomized to intermittent fasting with caloric restriction. We had a caloric restriction group, so they were energy matched and provided all their foods. And then we had a group of intermittent fasting people that were not energy restricted, so no caloric restriction. And then we had the control group. So the, the intermittent fasting group fasted for three days per week from 8am so they had breakfast and then they fasted for 24 hours and then, and then the next day ate the intermittent fasting restricted people aided about energy balance. And that is providing the same amount of calories as 70% restriction every day.
These are all women though, right? Just to be super. Okay, that's really unusual because not that many people have done women fasting studies, especially with the degree of comparing 70% of normal calories, 100% of normal calories. Kind of summarize the results for listeners because this is really important science.
Well, we saw that intermittent fasting 70, so the caloric restriction, intermittent fasting really, it outperformed caloric restriction in terms of weight loss and in terms of improving health. So it was unexpected. We did not, we thought that providing all the foods to everyone and we actually didn't want to get weight loss. We wanted to have exactly the same amount of weight loss in both the groups. So we could see whether intermittent fasting is beating caloric restriction without being different for body weight. And you know, the science never works out as you plan it exactly. But so we did see that the intermittent fasting group lost a little bit more weight than the cholera restriction group and they had better improvements in their health. So greater reductions in diabetes risk markers and greater reductions in cardiovascular risk markets than the calorie restriction group. So yeah, we, we proved that hypothesis, but we did get a little bit more weight loss than we wanted in one group. So that makes us not be able to say is it the weight loss or is it the fasting, which is exactly what we wanted to do, which is, which is better. So yeah, it was a little bit disappointing in the end.
But the interesting, the women in the study though, it wasn't disappointing at all because most people are happy to lose some weight. So you did get a great outcome for the people in the trial, but the data hid from you. Okay, that's funny.
And what we saw really was they were doing great on the fasting day. So our ladies in that study, you know, it was an eight week trial. It wasn't long, long term. And in this case, I think more than 50% were very happy to do it. I think intermittent fasting was very new when we ran that trial too. So it had really only just come out. Michael Mosley's book had came out during the trial and so it was all over the media and they were excited to be a part of this study. And so I think that maybe that had something to do with it. I don't, I don't know. But they, they, they were very adherent and they had trouble eating on their eating days enough. All the food we gave them, so they weren't actually that hungry, had their fasting day, they did great on it, they were really compliant. And then they got to their eating day and they didn't need all the food we gave them. So that's why they lost that little bit more weight, I think, than, than the calorie restriction group. I don't think it was magic. I don't think that they had, you know, super metabolisms or anything like that. But, but maybe there were some appetite changes that makes them not be so hungry. And potentially it's ketones, potentially it's ghrelin. We don't, we don't know that they are, you know, even they're not that hungry the next day. They can't, they can't overeat. They don't want to overeat.
The hunger suppression part of fasting is very interesting. When I was, this is about 12 years ago, I was working out the principles on the bulletproof diet, which is a cyclical keto thing with intermittent fasting and a little bit of time restriction in it. And I said I'm going to eat 4,500 calories a day, but generally either have intermittent fasts for breakfast or only have fat and nothing else at breakfast. And it was so hard to eat that much food because you're just not hungry. But the reason I was eating so much as I was trying to say I'm eating enough calories to gain 20 pounds, but I'm only going to gain 3 pounds. Therefore the calories in calories out equation is just flawed. But, but what I did was I lost weight and I kept losing weight even on a stupid amount of calories, which this is not the bulletproof diet. But though, guys, for your listening, um, I don't recommend you overfeed at all. It's not good for you to overfeed. There's lots of evidence it's bad for you. Um, but I was just sort of trying to disprove something and I did it for probably long. Can do it eating when you're only hungry. And magically you probably do get caloric restriction, Sam.
