Ep. 38: Does Intermittent Fasting Work? (Leslie Beck interviews Dr. Ethan Weiss)
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Time-restricted eating is said to encourage weight loss and improve metabolic health. But how effective is it, really? In conversation with guest host Leslie Beck is Dr. Ethan Weiss, a cardiologist who studies human metabolism at the University of California, San Francisco. Dr. Weiss used to be a fan of intermittent fasting—until he conducted his own randomized controlled trial on humans. His findings may surprise you.
LINKS AND HIGHLIGHTS:
Dr. Ethan J. Weiss’s web page at UCSF, and his Twitter feed.
Dr. Weiss’s randomized control trial on the 16:8 form of intermittent fasting is published in JAMA Internal Medicine.
The study was featured in numerous different publications, including the New York Times and CNBC.
In the podcast, Dr. Weiss refers to research conducted on intermittent fasting and mouse studies by Satchin Panda. Here’s an interview with Prof. Panda.
Dr. Weiss referenced a leader in the field of early time-restricted eating named Courtney Peterson at the University of Alabama, Birmingham. Learn about her work.
EP. 38: Does Intermittent Fasting Work?
FINAL WEB TRANSCRIPT:
Christopher Shulgan: Christopher Shulgan here, executive producer of Eat Move Think. In this episode, we talk about intermittent fasting. That’s the healthy eating method that restricts the consumption of food for some period of the day.
Christopher Shulgan: The method is said to provide miraculous health benefits. People say it encourages weight loss and improves metabolic health. Various types exist—there’s 5:2, which entails fasting for two days a week. An alternate-day method is popular, as is something called 16:8, which compresses all of one’s eating between the hours of noon and eight p.m.
Christopher Shulgan: Dr. Ethan Weiss is a cardiologist who studies human metabolism at the University of California-San Francisco. He first began practicing time-restricted eating in 2014. He became so convinced of its benefits that he evangelized about it to other people. He noticed that comparatively few randomized controlled trials had been done on the effects of intermittent eating in humans, and so he decided to conduct his own.
Christopher Shulgan: To use the old clickbait cliché, what happened next will surprise you. It certainly surprised the New York Times, CNBC, and the many other media outlets that covered it. But we won’t give it away just yet—instead, we’re delighted to feature Medcan’s director of food and nutrition, Leslie Beck, in conversation with Dr. Ethan Weiss.
Leslie Beck: Well, thank you so much for joining me today, Ethan. I really appreciate your time.
Ethan Weiss: It's my pleasure. It's fun to be here.
Leslie Beck: So you were the lead author on a recent study about intermittent fasting that turned up surprising findings and has also gotten a lot of media attention. Before we get into that, how does a cardiologist come to conduct a nutrition study?
Ethan Weiss: That's a great question. Well, the honest answer is that I started off in a very different area of biology. And we did an experiment, and the experiment yielded a result that we didn't expect. And the result was that we made a genetic modification of a mouse and the mouse developed rip-roaring metabolic disease. And so I, 11 or 12 years ago, got fascinated with metabolic disease, and basically changed the entire direction of my research program to focus on metabolism.
Ethan Weiss: And over the years, I've gotten more and more interested in human metabolism. At that time, there was very little understanding of the relationship between these metabolic issues—be it obesity, type two diabetes, other things and cardiovascular disease. We knew that diabetes and obesity were risk factors. But it was hard to explain why a cardiologist would be interested in this stuff. Today, there are formal partnerships between the American College of Cardiology, the American Diabetes Association, American Heart Association, and there's a formal world of cardio-metabolic disease. You know, I ended up here accidentally, but I think it's a nice place to be.
Ethan Weiss: We know that all of these metabolic issues are tremendously important risk factors for developing cardiovascular disease. We still know, you know, despite everything else that's changing in the world, cardiovascular disease is still the leading cause of death worldwide. And so I think the more that we attempt to try and understand and appreciate why people end up developing disease, but then also trying to find tools to help people mitigate or modify their risk and reduce their risk is important. So now, you know, it's sort of my reason for being, is I want to try and understand, particularly lifestyle and nutrition interventions that might impact cardiovascular disease.
Leslie Beck: Tell me what got you interested in intermittent fasting in the first place? I've read it was about a mouse study. Can you talk about that?
Ethan Weiss: Yeah, sure. So it was indeed about a mouse study, or I guess it was really about a series of mouse studies. The lead investigator is a scientist by the name of Sachin Panda in Southern California. And he published some really exciting work back in 2012, 13, 14, using what we call time-restricted feeding in mice. And it was a series of articles showing initially that you could protect mice from developing metabolic disease related to diet-induced obesity or metabolic disease. And then eventually, he showed that you could not only protect them, but you could actually cure them.
Ethan Weiss: And the cool thing about that study—without going into too much detail—and what got me excited about it was that you could do all this, and the mice ate the same exact diet and the same exact number of calories. So all that was different was the time of day that they were eating, or the window of time that they were allowed to eat. And so it was kind of an interesting idea. And the take home was that the mechanism related to an increase in resting energy expenditure. So they were burning more calories at rest, doing nothing. So it seemed like one of these, like, too good to be true interventions that might afford people who are looking to lose weight or improve their metabolic health, an option that was not too terribly complicated.
Leslie Beck: I see. So that's how you got into it. And certainly time-restricted eating, which is one version of intermittent fasting is very popular today. You know, limiting your eating to that eight hour window. But there are other versions of intermittent fasting, too. Why do you think that time-restricted eating is so popular and trendy today? Is it because it's easier to follow? People think it's going to help them lose weight? What are your thoughts?
Ethan Weiss: Yeah, it's a great question. So those studies that he did got a lot of attention, there were a number of very, very prominent articles written the popular press, I think the biggest was an article written in the New York Times, I still remember the figure of a clock and a mouse. And as a result of all of the hype and excitement over these studies, many of us, including myself, decided to give this a shot. And many of us, including me, had success with it, anecdotally. And my personal success, I lost some weight, I don't remember exactly how much but I lost seven or eight pounds, felt better. And I think I had the reaction that a lot of people have when they do it, which is wow, this is actually pretty easy to do. And so I got excited just as a lot of other people did, that this had a lot of potential. So I think I started recommending it to friends and family and some patients, and really was ultimately sort of led to the kind of conclusion that I should probably be a little bit more cautious in making these kinds of recommendations until we had data on two-legged creatures, in humans.
Leslie Beck: Right.
Ethan Weiss: And that was sort of what motivated us to eventually do the study. As to why this has gotten so popular, I do think it's precisely because it's so easy to do. There's no fancy calculator, you don't have to measure your calorie intake, macros, there's nothing to it. It's just eat during this time of day and don't eat during this time of day.
Leslie Beck: Right, right. And so I understand you've been following it for six years now, since 2014. You've lost a little bit of weight. With respect to the weight loss benefits of intermittent fasting—and I have read that, yes, intermittent fasting overall, when they look at the studies can promote a weight loss, but no more effectively than, say, cutting your daily calories each day. Is that because—do you think people are eating fewer calories in that eight-hour window? Or as you said, the mouse study that they're burning more calories at rest when they eat within a certain window?
Ethan Weiss: Yeah. So I think the excitement for me was understanding that mice and people are very different in terms of metabolism, I thought it was unlikely that we would increase our resting energy expenditure while cutting calories, or while eating this way. It was possible, but one potential idea was, since we know that anytime a human being cuts calories and loses weight, that we have this programmed, incredibly strong evolutionarily-programmed response to actually reduce energy expenditure to keep us from starving to death. We know that anytime somebody loses weight or cuts calories, they're going to have a corresponding decrease in energy expenditure. So the question was well, maybe you would have a smaller decrease or no decrease or, you know, in a ideal world, you'd have an increase. So that was the idea. I think, as you mentioned, most people probably still sort of subscribe to the idea that the only real way to lose weight is to restrict calorie intake. And so the other possibility was, as you mentioned, if you're eating fewer meals, or eating during a smaller number of hours of the day, you have fewer opportunities. And so maybe, effectively, you are restricting calorie intake.
Leslie Beck: So let's get into your study now that was recently published, well, it was published the end of September. Tell us about the study. How did it work? And then after that I'll ask you about the findings.
Ethan Weiss: Yes. So as I mentioned, I was really motivated by this series of papers in mice. And what we decided was, we wanted to try as best we could to replicate the experiment that was done in mice. Again, doing metabolism or nutrition experiments in people is a lot more complicated than it is in a mouse, right? A mouse lives in a cage, you put the food in there, they eat what they eat, and it's very easy to manage that. It's not so easy in people, outside of the sort of very, very unusual circumstances of somebody being admitted to a metabolic ward. And we knew we were not going to do that. So our primary goal was to do something that we thought was going to be easy to do, and tractable, and that it represented a real world situation.
Ethan Weiss: And we focused our attention on defining two different prescriptions and comparing them, as opposed to trying to very precisely measure everything that people were eating. We did do some, I think, pretty intense phenotyping on a subset of the people. So we tried to measure a lot of different things in them to try to get at potential mechanisms if we did see a difference. But our primary goal was, if we recommend to people eat during this window, don't eat during this window, and then we recommend to a different group of people, eat during this time, what's the effect? And again, that was really motivated by what we saw as one of the main advantages or potential advantages of this intervention was that it's very simple and easy to follow. So what we wanted to do at the beginning was to test the recommendation, test the prescription. So that was the basic design. And it was, you know, initially sort of framed as a pilot study. We ended up—I don't know what you'd call it, I think it's probably beauty's in the eye of the beholder, but it was a relatively small study, and over a relatively short period of time, although standard for a short-term weight loss study. And yeah, like I said, we designed it so that our primary endpoint was going to be weight loss. And then we had this sort of smaller group of people that we did more intensive analysis on.
Leslie Beck: So you basically randomized people to either do time-restricted eating, and I read that it's between noon and eight p.m. And then the other group ate meals throughout the day at conventional times.
Ethan Weiss: That's right. Yeah.
Leslie Beck: Okay. And nobody counted calories, they just ate what they wanted, basically.
Ethan Weiss: Yeah, we made no recommendation about calories. We made no recommendation about diet. We made no recommendation about exercise. We told people to live their lives, and the only intervention, we wanted to really isolate this one variable.
Leslie Beck: So it was a three-month study. Tell me what you found after three months.
Ethan Weiss: What we found was, at least as per self-report, which was all we had, that it was indeed a relatively easy intervention to do. So I think it was roughly 83 percent or so of people who responded us said that they were able to do it, compared to 90-something percent. So there was a difference, but it was relatively easy to do compared to most diet interventions. Other than that, our primary endpoint, what we found was that there was no statistical difference between the amount of weight lost in the two groups. And it's important because I think, you know, this speaks to the value or the importance and to our commitment to using a proper control arm, to do a randomized trial with a control arm. We can talk a little bit more about how we thought about conceiving of that control arm. But we wanted to be able to actually say that if there were an advantage that would be different than what we saw in the control group. And we found no difference. Both groups did lose weight, statistically, they both lost a little bit of weight, but ...
Leslie Beck: A little bit.
Ethan Weiss: About a kilogram, I think, in our main group, and about, you know, I think six-, almost seven-tenths of a kilogram in the control group.
Leslie Beck: So you were quoted in the New York Times as being shocked by the results. Why were you shocked?
Ethan Weiss: Well, I think, you know, as much as I try to tell people and young people who get into science not to try to go out and confirm your hypothesis to fit the data to your hypothesis, I was a believer. And so our intention, our goal was to validate that this actually worked. And I was practising it myself. And I think I did have some bias, right? I had already recommended it to a lot of different people. I expected it was going to work, I drank the Kool Aid. So I really believed it. So I think when we unblinded the data and started to do the analysis, we were all quite surprised. In fact, Dylan Lowe who's the graduate student, former graduate student who's now graduated, who was the lead author on the study, he and I were reminiscing a couple of weeks ago about how back when we first started analyzing the data, we'd have these three-way conversations between us and this statistician. And we kept telling him to redo the analysis. We said, "Well, there must be something wrong, do it again. Do it this way." And at one point, he finally said to both of us, "Guys, I can do this analysis 300 different ways, but there's no difference. There's no effect."
Leslie Beck: Yeah. And so how did the study findings affect your own diet? Did you make some changes as a result?
Ethan Weiss: I did end up making changes. I stopped doing this form of, you know, time-restricted eating. Effectively, I started eating breakfast again.
Leslie Beck: Okay. There was another finding that made lots of news headlines that you haven't discussed. I also read that the people who did the intermittent fasting, actually 65 percent of the weight they lost, albeit it wasn't a lot of weight, was from muscle. Can you talk to that?
Ethan Weiss: Yeah. So I want to be clear here. Let me first say it wasn't really technically muscle. We can't determine that based on the imaging we use. If you want to be super technical about it, it's called fat-free mass. So you can measure fat mass on a DEXA scan, you can measure fat-free mass. We can make some adjustments and call it "lean mass." And actually, the real difference was in appendicular lean mass. And that means on the appendages, so the arms and legs. And what we saw was that there was a greater decrease in lean mass in the time-restricted eating group compared to the consistent meal timing group.
Ethan Weiss: And I want to just say a couple of things that are sort of inside baseball about clinical trials. One was, because we measured several hundred variables, there are some we haven't even analyzed and published yet. We measured quite a number of things. Even the DEXA scan alone, I think has, like, 30 variables in it. We measured a bunch of different blood markers. We measured energy expenditure, both resting energy expenditure, total energy expenditure. We had people wear Oura Rings, and we measured activity, we measured sleep, we measured—it's literally hundreds of variables. And because people are familiar with this idea that a P value less than 0.05 means that there's a five percent chance that your finding, if it's positive, is a false positive. So that's the ...
Leslie Beck: It could have just happened by chance.
Ethan Weiss: By chance.
Leslie Beck: Yeah.
Ethan Weiss: And what that means is that if you do 100 experiments, you're going to have five of them that are going to be false positives, they actually are not—they're not real. And so because of that, statisticians have developed this methodology to correct for what they call multiple hypothesis testing. So if you do 100 experiments, you have to take a statistical penalty to avoid this possibility that you're actually getting these results by chance. And so it's corrected. Basically, you overcorrect. So the P value, instead of being—the threshold being 0.05, maybe it's 0.001 or something like that.
Ethan Weiss: So when you're doing clinical science like this, you're asked to pre-define what your endpoints are. And so we had a predefined primary endpoint. We had several, I think, eight predefined secondary endpoints. And among those secondary endpoints, we did correct for multiple hypotheses. So what I'm saying is that that difference in appendicular lean mass was actually validly corrected. It wasn't among the several hundred other variables that were uncorrected. The rest of the information in our paper, the rest of the variables in our paper were not corrected. So we'll talk a little bit later probably about some other things that showed up as being different, that we can't say really are different because of this problem. But in this case, we did see this difference in appendicular lean mass. And as you mentioned, of the weight that people lost, a large proportion of that weight did come from non-fat.
Leslie Beck: Non-fat, lean mass. To put it into layman's terms, you're finding around—the people in the intermittent-fasting group lost more lean mass than the other group. Your methodology, statistical methodology means that that finding actually is very valid. Is that what you're saying?
Ethan Weiss: Yeah, we have high confidence that it's real.
Leslie Beck: Okay. Perfect.
Ethan Weiss: I think there are some other things in there that I'm not as confident are real. In fact, I have very little to no confidence that they're real. But this one I'm quite confident is real.
Leslie Beck: So we also hear that intermittent fasting, besides you read it has weight-loss benefits, that it has benefits for your metabolic health: improved blood sugar, insulin, blood cholesterol, and so on. What did your study find? Now I understand these were your secondary endpoints you were looking at.
Ethan Weiss: That's right. And again, it was a smaller subgroup of people. It was only 50.
Leslie Beck: Okay.
Ethan Weiss: It was—I can't remember the number, but it was roughly half that actually had come in to do all this analysis. So half the people—everybody got a wireless scale, and the primary endpoint was derived from the weights from those wireless scales. So of the 116 people who completed, those are the data we used. And then roughly half the people also came into our lab, and had all these other things, including blood tests and DEXA scans.
Leslie Beck: Blood work. Yeah.
Ethan Weiss: So to make a very, very long story short, we found nothing. And there was no meaningful difference in any of these other markers, again, among the eight that we pre-specified to be key secondary endpoints. So including insulin, glucose, any lipids. I mean really, anything that you could think of, there was just no difference.
Leslie Beck: Okay, so intermittent fasting. No difference in body weight, no difference in cholesterol, blood sugar, insulin, all of those other metabolic health markers.
Ethan Weiss: Correct.
Leslie Beck: So I'm intrigued with early time-restricted eating or circadian rhythm fasting. When your eight-hour window starts earlier in the day versus, say, at noon. And eating this way, you read it really matches our body's biological clock or circadian rhythm. Can you talk a little bit about early time-restricted eating?
Ethan Weiss: Yeah, I'm also quite intrigued by it. I think the leader in that field is a investigator at University of Alabama-Birmingham named Courtney Peterson. And she's done and is continuing to do a number of studies on early time-restricted eating. We did briefly consider using an earlier feeding window or eating window in our study, because of the sort of—her data and other data suggesting that there may be advantages. Now we didn't consider this possibility that there may be a harm signal or potential harm signal. Again, you can use whatever language you want around the loss or relative loss of lean mass. We weren't thinking about that. In retrospect, I think that may be very important, so their timing may be important relative to the lean mass findings. But we were thinking that it may be advantageous for other metabolic benefits. We decided ultimately not to do that, because of the convenience factor, right?
Ethan Weiss: In our culture, breakfast is a meal that few of us eat with other people around. It's a very unsocial or antisocial meal, whereas dinner is a very social meal. And so I sort of went through the exercise of imagining that I sat down to dinner with my family and had a glass of water and watched them eat, right? And turned a participation sport into an observation sport. And so we felt like it was—while there were sort of scientific reasons to consider doing it, that the practical reasons made it something we didn't choose to do for this first study.
Leslie Beck: I see. So early time-restricted eating, explain to our listeners why eating earlier in the day and finishing earlier may be better for our metabolic health, perhaps weight loss.
Ethan Weiss: Yeah, we don't know. And in fact, there's an abstract for the upcoming Obesity Society meeting, and Dr. Peterson's group is presenting on that. And I can't remember the details off the top of my head, but it's a published abstract. And I don't think there was a statistical difference between weight loss. I think they did see some other things, improvements in maybe body composition. But, you know, the idea is that our bodies are primed to—you know, sort of all of the mechanisms of acquiring calories and storing them are more primed to happen in the morning. And there's this sort of borderline wive's tale idea that you don't want to have a huge meal right before you go to bed, that it may have adverse impacts. The truth is, we just have no idea. I don't think it's ever really been studied adequately enough, at least I don't know of any studies comparing them directly. Courtney's done some small studies that I think are really intriguing about it. And there are certain hormone responses, right? We know that there are circadian rhythms that, for example, growth hormone and cortisol are both secreted earlier in the morning. So when it comes to muscle synthesis, I do think there's very biologically-plausible explanations that muscle synthesis may happen predominantly in the morning, and so that it would make sense to have more substrate, more protein around to be able to make that muscle.
Leslie Beck: At breakfast, yeah. Okay. So why do you think that people in the intermittent fasting group may have lost more muscle compared to people in the conventional eating times group? What's going on there?
Ethan Weiss: Yeah. Again, I just want to be careful that we didn't technically find that they lost more muscle. For the purpose of this discussion let's talk about muscle, because I think the likeliest result is that it is muscle. We didn't formally prove that it's muscle. It could have been, I guess there's a small chance it could have been water or glycogen. But let's just have the conversation about muscle. Let's pretend that we actually did show that there was a decrease in muscle mass. So why is that? Well, we don't know. But we do have some hypotheses, and they all relate to protein, either protein amount or protein timing.
Ethan Weiss: So I think there are some interesting studies showing that people tend to eat a relatively fixed amount of protein per meal. And so if you cut a meal, you're cutting protein. There are other studies showing that if you're cutting calories, you may cut more protein. So one hypothesis is that people were eating less protein because they were having fewer meals.
Leslie Beck: Right.
Ethan Weiss: The second hypothesis is that it has something to do with timing of protein. There are some really interesting small studies, mechanistic studies, showing that new muscle synthesis occurs in the morning. So there was a beautiful study that we cited in our paper, that randomized people to two different interventions. One was where they had all their protein spread out equally across the day, and one was where they had their protein skewed towards later in the day. And then they did muscle biopsies on these people and measured the amount of new muscle that they were making. Now remember that we're constantly making and breaking down muscle, it sort of seems like a futile cycle, right? Why would we be doing that? But we do. And we do that with many different biological pathways. So it's not just you make new muscle when you eat, you're constantly making new muscle and breaking it down. And so they measured the amount of new muscle synthesis with the people who skewed their protein intake later in the day and it was decreased. Now they did not measure muscle mass. They did not do it long enough to be able to detect a difference in total muscle, but they did show that the amount of new muscle being made was reduced when you skewed the protein intake later in the day.
Leslie Beck: Yeah, a little bit of protein at breakfast, more at lunch, and most of it at dinner.
Ethan Weiss: Exactly. And that makes sense if you think that some of these hormones that are important in building muscle, like cortisol or growth hormone and other things, are largely priming the system to be able to do that, for that machinery to be active in the morning. So I think it's an interesting finding. It's definitely something that we would like to continue to explore.
Leslie Beck: Yeah, it is very interesting. So where does this leave us now? There really is very little evidence, if at all, that intermittent fasting or time-restricted eating improves your metabolic health, helps you lose weight. So where do we go from here? You know, what about other forms of intermittent fasting, the 5:2 diet, for example, or alternate-day fasting?
Ethan Weiss: Yeah, I would love to be able to speculate. But I've sort of made that mistake once now, and I'm not going to do it again. So I will say what we found was that this form, or a recommendation to do this form of time-restricted eating—so eating only between 12 and 8 p.m.—didn't work. And there was a potential signal for—I wouldn't call it harm, but it was something to keep an eye on in terms of this muscle thing.
Leslie Beck: The lean mass.
Ethan Weiss: So I think from my perspective, the potential of this, the reason we all got so excited about it was that it was easy to do. And it seemed like you could broadly apply it to large populations of people. I think I'm less convinced now that that's going to happen. So I think there's a lot left to explore, I think that we've talked about the timing. So you could change the window, you can change the number of hours that you're fasting, you can change the regimen even in more extreme ways, right, by fasting every other day, or fasting two days a week or—I have some patients of mine who fast for one week at a time doing only water. So none of that's been studied in a real way. And so I think there's a lot left there. I'm personally very interested in trying to understand if there's an interaction between when we eat and what we eat. So I'm interested in understanding if there's an interaction between diet and meal timing. And so that's an area that I'd like to explore going forward.
Leslie Beck: So what are you doing now specifically with your diet? You said you're eating breakfast. Have you made any other changes based on some of the hypotheses you mentioned, especially around protein?
Ethan Weiss: Nope.
Leslie Beck: Nope. Okay.
Ethan Weiss: No. I really just added breakfast back. I haven't thought so much about adjusting the other two meals that I eat during the day. I've never been a snacker. And I didn't really make any other changes. I just started having breakfast again.
Leslie Beck: So lastly, there are many people out there who want to adopt some sort of eating pattern that's going to help them with weight loss. If not intermittent fasting, what would you recommend those folks?
Ethan Weiss: [laughs] You're not going to get me to bite on that one. I'm not making that mistake again. I mean look, there's abundant evidence on, you know, some of the more popular diets. One thing I would say, is that there was very little, very little data on intermittent fasting. There were some small studies, mostly uncontrolled. There were a few controlled studies, but really small and short durations. And so I think, you know, the amount of data we have on pulling that lever of meal timing is relatively small and has been small. And so I think there were a lot of people doing this in the absence of data. Now these other diets, you know, whatever you want to call it: vegan diet, low-
fat diet, low-carb diet, there is actually a healthy amount of data. I mean, there are good data, I think, on all these diets, I think there are personal preferences, and there's probably a sort of—a diet that works for some people better than it works for other people. But I think there are abundant studies showing that there are diets out there that are effective. The key, of course, with all diets, as you know well, is not can you lose some weight, but can you maintain it?
Leslie Beck: Can you follow it?
Ethan Weiss: Yeah.
Leslie Beck: Yeah. Is it sustainable? Right.
Ethan Weiss: Look, what I would be interested in is more rigour in nutrition science, I think what we're missing here. Look, I think one thing that came out of our study that I took away from it, and I brought to it, right? I mean, we had a commitment to do it this way from the beginning, was the presence of this control group. And again, in nutrition, it's very difficult to do a proper control group, because you can't blind people, right? You can't just give somebody a placebo pill on an active drug, because they know what they're putting in their body every day. So we had to come up with sort of a trick to try to make it feel like the control group was not controlled. That's the other problem with these nutrition studies was that if you sign up to do a nutrition study and it's randomized, and you get randomized to a control group, you're going to quit, right? I mean, no one wants to spend 12 weeks of their life doing something that's nothing.
Ethan Weiss: So we did have to kind of make it feel like both of these were active interventions, which is why we ended up calling it consistent meal-timing, and we made these windows that felt like there was something to it. And I will say—I've said it many times in many different interviews, but I'll say it again here, if you look at the individual participants in our study across both groups, the person who lost the most weight was somebody who was randomized to CMT, to the control group. That person lost eight percent of their weight. And that ends up being on average—I don't know the exact number for that individual, but if you take by the average of starting weight, that's about 17 and a half pounds. It was over a pound, almost a pound and a half a week. The average weight loss in the TRE group among all the participants was about 0.2 pounds per week. So, you know, I think the important thing, and the reason we decided to do this as we did was to try to be able to say, well, what was the actual impact of this intervention? Not just being in a diet study, which we know will lead to some weight loss? So I think, you know, one thing I would love is more rigour in nutrition science, which I think we can do. I mean, I think we showed that you can do this. And there are—I'm excited to keep going. Like, I'm excited to—we've got more coming. And there are lots of different questions to answer. And everybody wants the answers. And so yeah, I mean, I think there's a lot left.
Leslie Beck: Yeah. And I think your point is—and you mentioned it earlier—that there was a control group in this randomized control trial, so you could really look at the intervention. The other thing I wanted to just clarify for our listeners is that the people in the CMT group, you know, they ate their meals at conventional times during the day. I think I read they ate three meals a day, they might have had a couple of snacks in there. And there was no difference in the calorie intake between the time-restricted eaters and the regular eaters if I will. That's true?
Ethan Weiss: That's right. Yep. There was really no difference in energy expenditure. We did some fancy—two kinds of measuring energy expenditure, and there was no difference in energy. They both had a decrease in energy expenditure as you would expect in people who lost weight, right? It's an evolutionarily-conservative process. You know, it would be bad if you started spending more energy as you started to get hungry. If you were starving—if you were out in the wild and you couldn't find food, you wouldn't want to turn up energy expenditure, you'd want to turn it down. Which is what we do. So both groups turned it down. There was no difference between the amount that they turned it down. They both turned down—they both basically turned the rev of the engine down. But there was no difference.
Leslie Beck: Well, thank you so much for being with us today. I really appreciate your time again. And it's been a fascinating discussion. Thank you so much, Ethan.
Ethan Weiss: Sure. My pleasure. Thank you.
Christopher Shulgan: That’s it for this episode of Eat Move Think. Follow Dr. Ethan Weiss on Twitter @ethanjweiss. Follow Leslie Beck on Twitter @lesliebeckrd. Check out the podcast website for highlights and full episode transcripts at eatmovethinkpodcast.com.
Christopher Shulgan: Eat Move Think is produced by Ghost Bureau. Senior producer is Russell Gragg. Social media support from Emily Mannella. Editorial direction from Chantel Guertin. Remember to rate and subscribe to Eat Move Think on your favourite podcast platform. Follow Shaun on Twitter and Instagram @shauncfrancis—that's Shaun with a U—and Medcan @medcanlivewell. We'll be back soon with a new episode examining the latest in health and wellness.
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