Time-Restricted Eating Put to the Test

Time-Restricted Eating Put to the Test
4.91 (98.24%) 91 votes

Are there benefits to giving yourself a bigger daily break from eating?

Discuss
Republish

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The reason many blood tests are taken before eating after an overnight fast is that meals can tip our system out of balance, bumping up certain biomarkers for disease such as blood sugars, insulin, cholesterol, and triglycerides. Yet fewer than 1 in 10 Americans may even make it 12 hours without eating. As evolutionarily unnatural as eating three meals a day is, most of us are eating even more than that. One study using a smartphone app to record more than 25,000 eating events found that people tended to eat about every 3 hours over an average span of about 15 hours a day. Might it be beneficial to give our bodies a bigger break?

Time-restricted feeding is “defined as fasting for periods of at least 12 hours but less than 24 hours.” This involves trying to confine calorie intake to a set window of time, typically 3–4 hours, 7–9 hours, or 10–12 hours a day, resulting in a daily fast lasting 12-21 hours. When mice are restricted to a daily feeding window, they gain less weight even when fed the exact same amount. Rodents have such high metabolisms, though, that a single day of fasting can starve away as much as 15 percent of their lean body mass. This makes it difficult to extrapolate from mouse models. You don’t know what happens in humans until you put it to the test.

The drop-out rates in time-restricted feeding trials certainly appear lower than most prolonged forms of intermittent fasting, suggesting it’s more easily tolerable. But does it work? If you have people even just stop eating between 7 p.m. and 6 a.m. for two weeks, they lose about a pound each week, compared to no time restriction. Note: no additional instructions or recommendations were given on the amount or type of food consumed; no gadgets, calorie counting, or record-keeping. They were just told to limit their food intake to the hours of 6 a.m. through 7 p.m., a simple intervention, easy to understand and implement.

The next logical step was to try putting it to the test for months instead of just weeks. Obese men and women were asked to restrict eating to the eight-hour window between 10 a.m. and 6 p.m. Twelve weeks later, they had lost seven pounds. This deceptively simple intervention may be operating from a number of different angles. People tend to eat more food later in the day, and higher-fat foods later in the day. By eliminating eating in the late evening hours, one removes prime-time snacking on the couch, a high-risk time for overeating. And indeed, during the no-eating-after-7-p.m. study, the subjects were inadvertently eating about 250 fewer calories a day. Then, there are also the chronobiological benefits of avoiding late-night eating.

I’m going to do a whole series of videos about the role our circadian rhythms have in the obesity epidemic, how the timing of meals can be critical, and how we can match meal timing to our body clocks. Just to give you a taste, the exact same number of calories at dinner is significantly more fattening than the same number of calories eaten at breakfast.

Calories in the morning cause less weight gain than the same calories given in the evening. A diet with a bigger breakfast causes more weight loss than the same exact diet with a bigger dinner. Nighttime snacks are more fattening than the same snacks in the daytime. Thanks to our circadian rhythms, metabolic slowing, hunger, carbohydrate intolerance, triglycerides, and a propensity for weight gain are all things that go bump in the night.

What about the fasting component of time-restricted feeding? There’s already the double benefit of fewer calories and avoiding night-time eating. Does the fact that you’re fasting for 11 or 16 hours a day play any role, considering the average person may only make it about 9 hours a day without eating? How would you design an experiment to test that? What if you randomized people into two groups, and forced both groups to eat the same number of calories a day and both to eat late into the evening, but with one group fasting even longer—20 hours? That’s exactly what researchers at the USDA and National Institute of Aging did.

Men and women were randomized to eat three meals a day, or to fit all those same calories into a four-hour window between 5 p.m.  and 9 p.m.  and fast the rest of the day. If the weight-loss benefits from the other two time-restricted feeding studies was due to the passive calorie restriction or avoidance of late night eating, then presumably both these groups should end up the same, because they’re both eating the same amount, and they’re both eating late. But that’s not what happened. After eight weeks, the time-restricted feeding group ended up with nearly five pounds less body fat. About the same number of calories, but they lost more weight. A similar study with an eight-hour window resulted in three pounds more fat loss. So, there does seem to be something to giving your body daily breaks from eating around the clock.

Because that four-hour window was at night, though, they suffered the chronobiological consequences—significant elevations in blood pressures and cholesterol levels—despite the weight loss. The best of both worlds was demonstrated in 2018: early time-restricted feeding, eating with a narrow window earlier in the day, which we’ll cover next.

Please consider volunteering to help out on the site.

Image credit: Monoar Rahman Rony via pixabay. Image has been modified.

Video includes graphics from Vecteezy.com

Motion graphics by Avocado Video

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

The reason many blood tests are taken before eating after an overnight fast is that meals can tip our system out of balance, bumping up certain biomarkers for disease such as blood sugars, insulin, cholesterol, and triglycerides. Yet fewer than 1 in 10 Americans may even make it 12 hours without eating. As evolutionarily unnatural as eating three meals a day is, most of us are eating even more than that. One study using a smartphone app to record more than 25,000 eating events found that people tended to eat about every 3 hours over an average span of about 15 hours a day. Might it be beneficial to give our bodies a bigger break?

Time-restricted feeding is “defined as fasting for periods of at least 12 hours but less than 24 hours.” This involves trying to confine calorie intake to a set window of time, typically 3–4 hours, 7–9 hours, or 10–12 hours a day, resulting in a daily fast lasting 12-21 hours. When mice are restricted to a daily feeding window, they gain less weight even when fed the exact same amount. Rodents have such high metabolisms, though, that a single day of fasting can starve away as much as 15 percent of their lean body mass. This makes it difficult to extrapolate from mouse models. You don’t know what happens in humans until you put it to the test.

The drop-out rates in time-restricted feeding trials certainly appear lower than most prolonged forms of intermittent fasting, suggesting it’s more easily tolerable. But does it work? If you have people even just stop eating between 7 p.m. and 6 a.m. for two weeks, they lose about a pound each week, compared to no time restriction. Note: no additional instructions or recommendations were given on the amount or type of food consumed; no gadgets, calorie counting, or record-keeping. They were just told to limit their food intake to the hours of 6 a.m. through 7 p.m., a simple intervention, easy to understand and implement.

The next logical step was to try putting it to the test for months instead of just weeks. Obese men and women were asked to restrict eating to the eight-hour window between 10 a.m. and 6 p.m. Twelve weeks later, they had lost seven pounds. This deceptively simple intervention may be operating from a number of different angles. People tend to eat more food later in the day, and higher-fat foods later in the day. By eliminating eating in the late evening hours, one removes prime-time snacking on the couch, a high-risk time for overeating. And indeed, during the no-eating-after-7-p.m. study, the subjects were inadvertently eating about 250 fewer calories a day. Then, there are also the chronobiological benefits of avoiding late-night eating.

I’m going to do a whole series of videos about the role our circadian rhythms have in the obesity epidemic, how the timing of meals can be critical, and how we can match meal timing to our body clocks. Just to give you a taste, the exact same number of calories at dinner is significantly more fattening than the same number of calories eaten at breakfast.

Calories in the morning cause less weight gain than the same calories given in the evening. A diet with a bigger breakfast causes more weight loss than the same exact diet with a bigger dinner. Nighttime snacks are more fattening than the same snacks in the daytime. Thanks to our circadian rhythms, metabolic slowing, hunger, carbohydrate intolerance, triglycerides, and a propensity for weight gain are all things that go bump in the night.

What about the fasting component of time-restricted feeding? There’s already the double benefit of fewer calories and avoiding night-time eating. Does the fact that you’re fasting for 11 or 16 hours a day play any role, considering the average person may only make it about 9 hours a day without eating? How would you design an experiment to test that? What if you randomized people into two groups, and forced both groups to eat the same number of calories a day and both to eat late into the evening, but with one group fasting even longer—20 hours? That’s exactly what researchers at the USDA and National Institute of Aging did.

Men and women were randomized to eat three meals a day, or to fit all those same calories into a four-hour window between 5 p.m.  and 9 p.m.  and fast the rest of the day. If the weight-loss benefits from the other two time-restricted feeding studies was due to the passive calorie restriction or avoidance of late night eating, then presumably both these groups should end up the same, because they’re both eating the same amount, and they’re both eating late. But that’s not what happened. After eight weeks, the time-restricted feeding group ended up with nearly five pounds less body fat. About the same number of calories, but they lost more weight. A similar study with an eight-hour window resulted in three pounds more fat loss. So, there does seem to be something to giving your body daily breaks from eating around the clock.

Because that four-hour window was at night, though, they suffered the chronobiological consequences—significant elevations in blood pressures and cholesterol levels—despite the weight loss. The best of both worlds was demonstrated in 2018: early time-restricted feeding, eating with a narrow window earlier in the day, which we’ll cover next.

Please consider volunteering to help out on the site.

Image credit: Monoar Rahman Rony via pixabay. Image has been modified.

Video includes graphics from Vecteezy.com

Motion graphics by Avocado Video

Doctor's Note

Isn’t that mindblowing about the circadian rhythm stuff? Calories in the morning count less, and are healthier, than calories in the evening. So if you’re going to skip a meal to widen your daily fasting window, skip dinner instead of breakfast. I’ll get to the best-of-both worlds study next in The Benefits of Early Time-Restricted Eating.

If you missed any of the previous 12 videos in this fasting series, here they are:

If you missed my last video of the day, it’s the exciting announcement that How Not to Diet is hitting shelves on December 10. Check out the book trailer here, and you can still pre-order the book to get it right when it comes out.

If you haven’t yet, you can subscribe to my videos for free by clicking here.

48 responses to “Time-Restricted Eating Put to the Test

Comment Etiquette

On NutritionFacts.org, you'll find a vibrant community of nutrition enthusiasts, health professionals, and many knowledgeable users seeking to discover the healthiest diet to eat for themselves and their families. As always, our goal is to foster conversations that are insightful, engaging, and most of all, helpful – from the nutrition beginners to the experts in our community.

To do this we need your help, so here are some basic guidelines to get you started.

The Short List

To help maintain and foster a welcoming atmosphere in our comments, please refrain from rude comments, name-calling, and responding to posts that break the rules (see our full Community Guidelines for more details). We will remove any posts in violation of our rules when we see it, which will, unfortunately, include any nicer comments that may have been made in response.

Be respectful and help out our staff and volunteer health supporters by actively not replying to comments that are breaking the rules. Instead, please flag or report them by submitting a ticket to our help desk. NutritionFacts.org is made up of an incredible staff and many dedicated volunteers that work hard to ensure that the comments section runs smoothly and we spend a great deal of time reading comments from our community members.

Have a correction or suggestion for video or blog? Please contact us to let us know. Submitting a correction this way will result in a quicker fix than commenting on a thread with a suggestion or correction.

View the Full Community Guidelines

  1. This is probably for people not eating whole food plant-based diets? I continually eat throughout the day because if I don’t I will probably lose more weight and my BMI is around 21. I don’t think I could comfortably get enough calories in a Time restricted window.

    1. Might it be that your are eating mainly the plant components of the Acheulian diet (nuts, seeds, cooked plants, little tubers etc) form 800ka years ago and not the Homo Sapiens diet (mainly cooked starches), from 300ka-100ka ago:

      From the article “Earliest evidence of the cooking and eating of starches”:

      “Starch diet isn’t something that happens when we started farming, but rather, is as old as humans themselves,” says Larbey. Farming in Africa only started in the last 10,000 years of human existence. Humans living in South Africa 120,000 years ago formed and lived in small bands. “Evidence from Klasies River, where several human skull fragments and two maxillary fragments dating 120,000 years ago occur, show that humans living in that time period looked like modern humans of today. However, they were somewhat more robust,” says Wurz.

      https://www.sciencedaily.com/releases/2019/05/190517115142.htm

    2. DavidW,

      I too eat all throughout the day, but small meals and even smaller snacks. I consider it as about 3 normal meals, but spread out. And my weight is fine — right in the middle of the BMI (because I’m shrinking! Worsening scoliosis doesn’t help.) Oh, and I eat whole plant foods, avoiding animal products and most processed foods, as well as added sugar, oil, and salt.

      In fact, I don’t do fasting blood tests, and haven’t for years. Because I think I’m slightly hypoglycemic, as well as needle phobic — a wicked combination early in the morning for blood tests! But, routine fasting blood tests are no longer recommended. There is apparently very little difference, at least for the lipid panels (as I recall), between fasting and non-fasting results. Fasting blood tests are done if any abnormalities are observed. So I’m surprised to see Dr. Greger mentioning them as routine. But then again, as he himself has frequently noted, it takes about 17 years from lab results to clinical practice, and these results are only a few years old.

    3. I’m pretty sure this article is for people who need to lose weight, rather than people not on a PBD. Even on a plant-based diet, weight loss is hard. Personally, I’ve lost only 20 lbs after being on PBD for a year. If I found something that worked with my schedule and I lost even just one pound a week, I would lose what I need to in 10 months. Maybe then, I’ll start to ‘worry’ about your point.

    4. I don’t eat past 7pm typically because I do feel better, but I eat when I get up when I feel like it. (In fact, I feel much better on an earlier schedule in general). I felt awful when doing the intermittent thing and basically needing to force myself to eat (in order to get proper servings in, such as in the daily dozen) when I wasn’t hungry. Contrary to feeling cleaner, I felt overwhelmed and more backed up. It really felt very unnatural and caused a lot of physical as well as psychological stress. I personally do not believe it is mentally healthy or particularly sustainable to make eating that complicated and “perfect.”

  2. This is the video I’ve been waiting for. I’ve been doing time restricted eating (noon to 6 pm) for so long that my body is totally used to it. I don’t get hungry until noon. I feel cleaner eating this way and find it’s easier to sleep when you’re not loaded down with food. Looking forward to the next video.

  3. What about restricted time eating for athletes who train twice per day, for example from 6:30 am to 8:30 am, and 7:30 pm to 9 pm?
    Is it benificial to keep fasting after training? Or is it more important to reload, even if it is later at night?

    1. Aiman I heard that working out while fasting leads to better results. I would personally eat afterwards. You need to fuel up. I would repeat the same thing with you
      Next workout. Hopefully dr. Greger can answer that.

  4. I’m fasting from 7 pm until 11 am 16 – 8 I really gives your body the time to clean up an digest all of that food. I’m really interested in the new videos with the circadian rhythms. I do believe that fasting disrupts sleep.

  5. Dr. Greger, will all this fasting/circadian rhythm information be in “How not to Diet?” If so, I’m really looking forward to having it all put together! Pre-ordered on my Kindle –

  6. How could we possibly state as a fact that eating 3 meals a day is evolutionarily unnatural? And what happened to the theory of our ancestors eating fruit and foliage all day long? I don’t care how many feces fossils are collected and how many ideas make promising theories, it just seems impossible to factually know how many times a day our collective—as in throughout the globe—ancestors ate.

    1. I wouldn’t take too much notice of what our ancestors ate. The most important findings are of modern day science and biological markers from randomized tests.
      We are all human and can make our own choices. I eat PBD and fast 16 to 20 hours a day. I have more energy than when I was 20 years younger. Currently 56 with a young family.

      1. We do not know how they ate, but we have indications of what they ate. Also, we have acquired genetic modifications related to starch digestion (salivary amylase) about 300ka ago, indicating more cooked starches into the diet.

      2. I’m glad that works so great for you, David, those are some really cool results. For me, when I tried intermittent fasting two separate and fairly long term times in my life, I felt substantially worse than how I do on my non-intermittent WFPB diet. I do like to stop eating past 7 or at least 8 on a regular basis (with some exception), though, because I find that I feel my best when I do.?typically that leaves about 11 hours of not eating (I do drink tea) on average sometimes more sometimes maybe a little less but I don’t worry about it which in and of itself is a healthy act for me.

        The thing is, is there are actually very few studies showing how fasting and other controlled diets compare to a whole foods plant based diet. So even if improved markers in health are shown in studies of people doing intermittent fasting, it can’t be said how it would look side-by-side to a non faster, WFPB person or even a fasting WFPB person.

  7. The various parts of the body need differing periods of R&R. The gut lining cells, which together with skin are exposed to the outside world, take a beating. The gut lining cells only live a couple of days before they are replaced. While the brain gets R&R while sleeping, the gut cells get R&R between meals, first they do their job digesting the food. Then it best to give the gut some recovery time before you hit it with another meal. That is why between meal snacking is not good for digestive health, and a long overnight fast is healthy for the gut.

    1. “That is why between meal snacking is not good for digestive health”

      Evidence, please.

      I have never had digestive problems from snacking between meals on a healthy plant diet. I only had digestive issues occur on this diet when I ate when I wasn’t hungry in trying to do intermittent fasting. As far as snacks go, I would guess that an apple between meals will be beneficial to digestion, for example, vs a corn dog. As far as digestion goes, it seems dependent on what you eat more than anything else.

    2. I have been eating between 8am and 5pm,approximately, for the past few months now. Three meals, on the small side, and sometimes just two, no snacks. I was just trying to cut down on eating out of habit vs being hungry. I feel much better, sleeping better, and manage to schedule around gym time comfortably.

      1. Am happy to hear you’ve been keeping it up, Barb. *thumbs up*

        But you’re stronger than I am. I still like to have my three squares. And those meals aren’t so “small.”

  8. In 2009, when I was unemployed, I fell into a 10am and 4pm meal pattern. It was the happiest meal pattern for my body. Too bad it is so difficult to follow that schedule while working full-time. I should try to work out a compromise that comes close.

  9. Funny thing: non-American cultures have known this for centuries. Relatives who live in Germany have always had a moderate breakfast. The “big” meal of the day is at noontime. In the evening, dinner was very light: some fruit, cheese, maybe sliced meats and then shut the mouth for a 10-12 hour fast. In parts of Mexico even today, the big meal is lunch followed by a siesta – what a nice way to live.

    1. Why would it be different? I’ve been doing intermittent-fasting for more than 6 months. I try to quit eating between 5pm-7pm & then eat at around 11am. It takes 12 hours of fasting, water is okay, coffee & tea are NOT, & then your body begins to cannibalize defective fat cells, including senescent cells in the brain, which have been related to cognitive disorders. I think this is a much more important reason to engage in intermittent-fasting, regardless of your work schedule. Your body gets very used to it. The only time it’s weird for me is Friday night dinner which is late, but I still try to finish eating by 8p or 9p, so even if I eat the next morning at 10:30am or 11am, I’ve still got my 12 hrs plus 1.5-2 of cannibalizing defective fat cells.

          1. It seemed to me that she was addressing two separate questions 1). black coffee 2). amino acid supplements

            Admittedly, coffee does contain trace amounts of some amino acids but the amount is so small as to be negligible.

    1. It’s absolutely not cheating to fast while you sleep! i usually fast 7 pm to 10 or 11 AM and have found it really helps me control my appetite. Feeling hungry is normal and we don’t have to eat every time we feel it a little. the problem is eating too close to bed and having your body not digest before it slows down to sleep.

  10. Why did the video at 5:00 mention significant elevations in blood pressure, but then list ~116/70 for the blood pressures in the group? That’s a very healthy blood pressure.

    1. Yes but it was higher than the 110/66 in the non TRF group.

      “Significant’ here means statistically significant (not ‘big’)

  11. I have more difficulty sleeping well than maintaining my weight. Does anyone find that Time Restricted Eating helps with insomnia, particularly sleep maintenance? I feel if I don’t have a light snack two hours before bed, I wake up hungry in the middle of the night. I often am awake in the middle of the night much of the time, regardless.

    1. Yes, but I have the opposite problem – I sleep badly if I eat too close to my bedtime. I need at least three hours without food before bed. I know he’s Oprah-trendy (Oprendy?), but Dr. Breus’s ideas about sleep have helped me considerably. He’s not a good person to listen to about nutrition, but on circadian patterns and related sleep issues, he is helpful. The animal chronotypes sound goofy, but for me, the description and suggestions were spot-on.

  12. Watching what David Sinclair has been discussing on various YT channels, he’s implying that with various nutraceuticals/drugs you could reverse ageing and eat a high fat diet. Some of the nutraceuticals include metformin, niacinimide mononucleotide and nicotinamide riboside, trans-resveratrol. It’s a little out there but with the vegan diet you have to take b-12 tablets so it’s not that much different. Except for the cost.

Leave a Reply

Your email address will not be published. Required fields are marked *

Pin It on Pinterest

Share This