Sofia Cienfuegos Muzard PhD - Exploring the Impact of Time-Restricted Eating on Weight Loss and Metabolic Health

Effects of 4- and 6-h time-restricted feeding in adults with obesity. 

BIO: Dr Cienfuegos is a Clinical Assistant Professor in Kinesiology and Nutrition at the University of Illinois at Chicago. Dr. Cienfuegos has a Ph.D. in human nutrition and has been studying intermittent fasting for the last seven years. Dr. Cienfuegos is an emerging expert in this field, with more than 30 publications in the most prestigious journals, such as Cell, Annual Reviews, and Nature. She has participated in several national and international scientific conferences and trained other professionals worldwide. Dr. Cienfuegos is the Co-I on two R01s (R01DK119783 and R01DK128180), examining the health benefits of fasting. 

Description of talk: Data from her Ph.D. work examining the weight loss efficacy of shorter TRE windows (4-h and 6-h TRE) was published in Cell Metabolism and received substantial media attention. She has extensive hands-on experience designing and coordinating R01-funded clinical trials and leading large research teams during recruitment, counseling, and data analysis. This seminar will focus on these original investigations.

Transcript

Speaker 1: 0:05

first of all, thank you so much for the invitation. I'm really excited to talk about this very um, popular topic. I'm gonna make sure that I don't go above the time, um, so I'm gonna go a little bit away from sports nutrition I mean it's still related but mainly I'm gonna talk about time-restricted eating related to weight loss and other cardiometabolic outcomes. I've been doing research in time-restricted eating for like the last seven, eight years and I work at the University of Illinois in Chicago as a clinical assistant professor. So let's start with one of the most complicated questions about defining what intermittent fasting is. Actually, there's not an official definition of what intermittent fasting is. Usually, what we say is a dietary approach that cycles between periods of fasting and periods of eating. Some of you might say well, I do that every day because I eat during the day and I kind of fast during the night. Well, yes, but technically, in order for that fast to be intermittent fasting, that fast should be longer than 12 hours and shorter than 24 hours. A little bit of debate on those 24 hours. Some people say 32 hours, some people 24 hours, but among that range you would be doing intermittent fasting Shorter than a 12-hour fast. You won't get those metabolic adaptations, and longer than 24 hours you would go into a different metabolic sort of scenario. That's different from intermittent fasting. So the main focus in intermittent fasting is when to eat, rather than what to eat, and this is something important that I want you guys to understand.

Speaker 1: 1:38

All of the things that I'm going to discuss in this presentation, it's going to be studies that we were focusing on the timing of food, but not on the types of food that people were eating. This is a question that I get very frequently. There's many different types of intermittent fasting. One of the first ones that started to be studied was called alternate day fasting. Well, you alternate days of fasting and days of feasting, and fasting and feasting. Well, feasting is your normal ad libitum dietary intake and your fasting days could be a complete fast or a very low calorie diet around 500-600 calories a day. Then the 5-2 diet it's two non-consecutive fasting days a week and the remaining days of the week you eat ad libitum.

Speaker 1: 2:21

Your normal diet and the most popular one, the one that I'm going to discuss today, the one that I've been focusing on, the one that I've been doing research on, is called time-restricted eating. And time-restricted eating you do it every day of the week and basically time-restricted eating is when you limit your eating window to a specific time frame. Each day could be between four to ten hours, and actually a study published by panda edal a couple years ago uh, from, I think it's enhanced data showed that most americans eat within a 16 hour eating window and fast for eight hours. So most people kind of start eating around 7 am and then they continue eating throughout the day and then around like 10 or 11 pm they stop eating. They have I don't know their last night snack after watching their show, whatever, and then they go to sleep and they fast during the night when they're asleep for about eight hours and then when they wake up they start eating again and this natural night fast. We know that it's been getting shorter and shorter. Years ago it used to be longer and now it's getting shorter and shorter because we're starting our days earlier and we're finishing our days later as well. So basically we know that this is not ideal in terms of metabolic health. There's a lot of research out there showing that late eating and prolonged eating windows are not ideal. There's a lot of data related to circadian rhythms.

Speaker 1: 3:48

I'm not going to go into that route, because that's a completely other presentation, very, very complex and long topic. But time-restricted feeding tends to revert this formula. Instead of eating for 16 hours and fasting for eight hours, we want to. Instead of eating for 16 hours and fasting for eight hours, we want to shorten that eating window to, let's say, eight hours that's the most common one and fast for a longer period of time. So it doesn't necessarily need to be eight hours of eating, 16 hours of fasting. Usually the eating window can go anywhere between four hours to 10 hours and the fasting window anywhere from 14 to 20 hours.

Speaker 1: 4:34

So intermittent fasting and specifically time-restricted eating has been getting a lot of popularity and probably all of you guys here know that. Yes, it's super popular, it's everywhere. Everybody's talking about it, people love it, people hate it. Very strong emotions towards it. It's very frustrating to be doing research on such a debated topic because, I mean, everybody seems to know a lot about it, but actually we don't have a lot of data yet.

Speaker 1: 4:59

So I'm going to show you what we have so far, you what we have so far. So I'm going to walk you through the different studies that we've done. I'm going to focus more on the one that I was asked to present, the one about short eating windows, but I'm going to show you the first one and the last few ones that we've also published. So this was the first eight-hour time-restricted eating study that we published 2018, it was really difficult to publish this study because in 2018, nobody cared about time-restricted eating. To publish this study because in 2018, nobody cared about time-restricted eating, at least not like today.

Speaker 1: 5:30

This was a short, small study doing an eight-hour window from 10 am till 6 pm. Compared to a control group, we measured different things Texas body weight adherence, metabolic disease markers, blood draws, weight, other things and we saw weight loss of around 2.6% and an intentional calorie restriction of around 350 calories a day. So this is something that's really important about time-restricted eating In these types of studies, we don't tell people what to eat, how many calories, what they should do nothing. We just tell them start eating at 10, stop eating at 6, and that's it. So in this study, just by saying that, people lost around 2.6% of their body weight, which was interesting Of course, not very significant weight loss, but still interesting considering the lack of dietary or calorie guidance. So then we came with the question Okay, so we know that an eight-hour window produces weight loss. What happens if we shorten that eating window even further? We do a four-hour or six-hour time-restricted eating, are we going to get even more pronounced weight loss results? And well, this is a study that I'm going to publish, that I'm going to go a little bit deeper today.

Speaker 1: 6:42

This is a study that I worked on while I was doing my PhD. I was very scared when I was doing this study, so I wasn't very sure if people were going to be able to do this. So we had a four-hour eating window and a six-hour eating window. People in the four-hour eating window were eating between 3 pm and 7 pm and fasting from 7 pm till 3 pm. So a four hour eating window, 20 hours of fasting, the six hour eating window. They were starting to eat at one, stopping at seven and fasting from seven till one, and a control group that they were not fasting and not changing anything from their usual habits.

Speaker 1: 7:21

Brief thing here it says time restricted feeding, trf. The term changed so whenever we started doing research here we're coming from animal studies. In animal studies it was called time-restricted feeding because you feed the animal. Now that we're moving into animal research, now the term changed to time-restricted eating because we don't feed humans. Humans eat so so now the term is time-restricted eating. Um, so this is the design of the study.

Speaker 1: 7:49

We measure different things dexas, body composition, body weight, adherence, um, how do we measure adherence for the four hour and the six hour eating window? Imperfectly, of course. These are studies done in free living conditions. There's's really really difficult to measure adherence to time-restricted eating. We give this log. People write down the date, at what time they started eating, at what time they stopped eating. We hope for the best. We really ask them to be honest and to really write what actually happened and then we check if it was adherent or not. In some of our later trials we've tried CGMs and other things and honestly, everything is really difficult to measure adherence in this population. But still this is what we have and it kind of works OK. We also do seven-day food records beginning, middle and end of the trial to measure their diet and how macro and micronutrients are changing after the intervention. And this is the flowchart for this study.

Speaker 1: 8:53

We screened 82 participants. 24 were excluded because they did not meet one or more inclusion criteria, 58 were randomized, 19 to a four-hour time-restricted eating, 20 to the six-hour, 19 to the control and we ended up with 16 completers in the four-hour, 19 completers in the six-hour and 14 completers in the control and actually we didn't have any dropouts due to disliking the diet. I was completely sure that at least in the four-hour group people were going to hate it and everybody was going to drop out because it's very brutal eating four hours. And actually no, we didn't. We didn't have any any dropouts and we saw weight loss. And this study was shorter than the study that I showed you a couple of slides ago. The other study was 12 weeks. This was just eight weeks. This was a short study. Weeks this was just eight weeks. This was a short study. Why? Because we were scared, we weren't very sure. This was the first study ever testing short eating windows and I, when I started this study, I was sure that everybody was going to drop out, so I didn't want it to do a really long study.

Speaker 1: 9:54

It was kind of a pilot study and we saw 3.2 percent weight loss in eight weeks, just two months, without any dietary advice, without any specific calorie restriction, without anything, just eat from this hour to this hour and they lost weight. Of course, this degree of weight loss doesn't sound that appealing in a world where GLP-1 receptor agonist drugs exist and we're seeing 25% weight loss. This amount of weight loss is not that amazing, but still it's weight loss without medications, without prescribed calorie restriction, without. It's just looking at the clock. Another thing that was interesting same amount of weight loss between the two groups. We thought that maybe the four hour time shifted eating group we're going to lose more weight because it was a shorter eating window. That didn't happen.

Speaker 1: 10:44

Most of the results were very similar for the two intervention groups, so we kind of concluded that a six-hour eating window might be the sweet spot In terms of adherence. Also, we were very surprised about it. People were able to do it, at least according to their self-report, but they were able to do it. They liked the intervention. Anecdotally, they liked the intervention. They suffered the first few weeks and they ended up liking the intervention and I think that's probably why intermittent fasting has grown so much in popularity. For some reason, people that do it not everybody, but some people that do it really like it and can do it kind of easily. In terms of insulin and insulin resistance results from this short eating window study, both intervention groups decreased fasting, insulin and insulin resistance significantly in just two months, and this is something that we've seen pretty consistent throughout most of the time-restricted eating studies that apparently in terms of insulin and glucose regulation it tends to have pretty good results.

Speaker 1: 11:45

Nothing in terms of blood pressure, plasma lipids and this is also something that we've seen pretty regularly Fasting, time-restricted eating does not seem to change dietary lipids, sorry, plasma lipids. Some studies have seen decreases in blood pressure, plasma lipids. Some studies have seen decreases in blood pressure, but in terms of lipids we haven't seen much and it's probably because we don't change the diet and lipids respond pretty directly to changes in dietary lipids. So, in terms of body composition, both groups decreased fat mass significantly relative to controls. In terms of lean mass, both groups lost a little bit of lean mass. It's similar to the amount of lean mass that you lose with any type of weight loss regimen, any type of dietary restriction. Around 25% of each kilogram loss is going to be of lean mass. However, something that was very strange in this study is that the six-hour lost more lean mass and significantly more lean mass relative to the four-hour eating window, which was very counterintuitive, strange.

Speaker 1: 12:56

I had a nightmare trying to write about this in the discussion of my article. So if any of you have any ideas, be happy to discuss about this in the discussion of my article. So if any of you have any ideas, be happy to discuss about that. And we also saw some reductions in oxidative stress markers, specifically 8-isoprostane, which is a marker of lipid peroxidation. So it's a marker of oxidative stress. Some other studies have seen similar things, which is interesting. We're not really sure mechanistic-wise if it's due to ketone body production, if it's due to vitamin E release from the gallipost tissue. We don't really know where it's coming from, but we know that some oxidative markers are improving after time-restricted eating.

Speaker 1: 13:35

And then, in terms of energy intake, this is the main sort of explanation why people lose weight during intermittent fasting, because people unconsciously restrict calories. So that's the main explanation. There's nothing very magical. It's people when you eat in less hours, you eat less food, and actually I wasn't expecting this because I thought that people were going to overeat during those four hours. These are patients with overweight, with obesity, actually with obesity, and I thought that people were going to overeat during those four hours. These are patients with overweight, with obesity, actually with obesity, and I thought that they were going to eat way more calories during those four hours. They were going to be starving and they were going to eat a lot of calories, and actually that doesn't happen. People do restrict calories when they eat in less hours. So in this study was around 550 calories less. So there was an unintentional calorie restriction of 550 calories, which is pretty significant. And for all of you guys that work in dietary or anything related to diet or nutrition, restricting 550 calories from a patient is really hard.

Speaker 1: 14:42

In terms of adverse events, we measured adverse events weekly and it was interesting to see that a lot of these adverse events increased the first week of the intervention. So a significant increase in dizziness, nausea, diarrhea, headaches, dry mouth, constipation the first week. So people were a little bit miserable the first week, the first two weeks, but then all of the adverse events tended to decrease and to even out and then people sort of got used to it. The only two ones that got a little bit higher so the trial was constipation and also dry mouth. Dry mouth was consistently high in the intervention groups and we're not really sure why, but when you're fasting for too long, probably you don't have the stimuli for saliva production. And the summary of the findings of this short eating window study similar findings, so both eating windows achieved very similar results. So in my opinion, with a six-hour window, you should be fine. You shouldn't go into a four-hour eating window. You're not going to get any added benefits, at least from this trial, and we don't have any newer data in really short eating windows 3% body weight loss in two months. Self-reported adherence was very high. An intentional calorie restriction of around 550 calories, reductions in insulin and insulin resistance, decreases in oxidative stress markers, but no effects on lipids or inflammation. So that's it with this study of short eating windows that I did during my PhD.

Speaker 1: 16:20

Now I want to briefly mention some newer studies that we've published. This study was published in cell in 2020, the one that the short eating windows but during these last few years we've been working in two big trials, so this one was published in 2023, last year in Annals of Internal Medicine, so this was kind of one of the first. It was a second, so, right when we're about to publish this one, someone else published a longer, time-restricted eating trial, but this one was a year long. So this was time-restricted eating eight-hour window versus a calorie restriction. The previous study that I mentioned. We're not comparing it to a calorie restriction here. We're comparing it to the gold standard a calorie restriction and no intervention control group for weight loss and cardiometabolic risk reduction. So it was 12 weeks lost. Sorry, 12 months long. So a year long. Six months of active weight loss, six months of weight maintenance, 90 adults with obesity. During the weight loss phase it was an eight-hour window and during the weight maintenance phase they switched to a 10-hour window. The calorie restriction was 25% restriction of their calorie needs a day. The control eating over 10 hours a day and what we saw? Similar results. So an eight-hour window achieves comparable results in terms of weight loss and all the other cardiometabolic risk markers, the same as the calorie restriction, which for a lot of people was demotivating and they were upset with this result and I honestly am not upset. I think it's really interesting to see that a study that is just an intervention, that's just looking at time, can achieve the same results as an intervention where people are actively counting and tracking calories, which is annoying for some people Not for everybody, but for some people really hate counting calories, so it is technically an alternative.

Speaker 1: 18:22

This is the latest one that we published Effect of Time-Retreated Eating on Weight Loss in Adults with Type 2 Diabetes. Also randomized controlled trial. We published this in JAMA Open a couple months ago. This was another study that another big question that we had can people with type two diabetes fast? We had zero data prior to this and we were very scared because of hypoglycemia.

Speaker 1: 18:48

So this study we compared time-restricted eating efficacy for weight reduction and glycemic control compared to calorie restriction in adults and a control group in adults with type 2 diabetes. Six months so not not a year long, six months 75 adults with type 2 diabetes and we saw significant weight loss and decreases in hba1c in both groups, not different between the calorie restriction and the time restricted eating group. So eating group. So both groups decreased HbA1c significantly and also weight loss both groups. Actually, here time-restricted eating looks like it achieved a little bit more weight loss, but it wasn't statistically significant. So comparable results in terms of weight loss as well. And one of my favorite results here because this is where we were very, very scared of was adverse events. And adverse events were not different between the time-restricted eating group and the calorie restriction group. So hypoglycemic events, hyperglycemic events all of those were practically the same.

Speaker 1: 19:53

So based on this study, we can say that time-restricted eating can be useful for people with type 2 diabetes to manage glucose markers HbA1c, and risks are not going to be higher than your traditional calorie restriction. However, this needs to be sort of followed by your physician because adjustment to the medications needed to be done, specifically those that were using insulin. So just to finish, who shouldn't fast? Fasting is not for everybody. It's not the most magical strategy in the world, as some people sort of frame it. It's just one more tool in our toolbox.

Speaker 1: 20:40

There are some people that shouldn't fast Pregnant women or lactating women. We don't have any safety data so we prefer to avoid it. Night shift workers we also exclude them from all of our studies and in terms of circadian rhythms, they would have to eat on a different time of the day, probably at night, so we don't know how those results would go. People with strict medication regimens that they need to eat at specific hours where they have to take that medication also shouldn't. People with a history of eating disorders we also exclude them in our studies and we're not sure if this restriction could start something new.

Speaker 1: 21:15

Children shouldn't and people who are normal weight, borderline low, lower weight, also shouldn't do intermittent fasting. It's really important for people to know that all of these studies have been done in an overweight, obese population. Uh, we don't have any data in normal weight people. We don't really know if it's safe or how it behaves. Um, and I hope that I'm okay with time. So acknowledgements thanks to my lab, dr, chris Averity, who I've been working with for the past eight years, and all my other lab members that did these studies and have been working together. So thank you so much for inviting me.