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Original Investigation
September 28, 2020

Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial

Author Affiliations
  • 1Cardiovascular Research Institute, University of California, San Francisco, San Francisco
  • 2Cardiology Division, University of California, San Francisco, San Francisco
  • 3Center for Vulnerable Populations, University of California, San Francisco, San Francisco
  • 4Clovis Oncology Inc, Boulder, Colorado
  • 5University of Hawai’i Cancer Center, Honolulu
  • 6University of California School of Medicine, San Francisco
  • 7Pennington Biomedical Research Center, Baton Rouge, Louisiana
JAMA Intern Med. 2020;180(11):1491-1499. doi:10.1001/jamainternmed.2020.4153
Key Points

Question  What is the effect of time-restricted eating on weight loss and metabolic health in patients with overweight and obesity?

Findings  In this prospective randomized clinical trial that included 116 adults with overweight or obesity, time-restricted eating was associated with a modest decrease (1.17%) in weight that was not significantly different from the decrease in the control group (0.75%).

Meaning  Time-restricted eating did not confer weight loss or cardiometabolic benefits in this study.


Importance  The efficacy and safety of time-restricted eating have not been explored in large randomized clinical trials.

Objective  To determine the effect of 16:8-hour time-restricted eating on weight loss and metabolic risk markers.

Interventions  Participants were randomized such that the consistent meal timing (CMT) group was instructed to eat 3 structured meals per day, and the time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day.

Design, Setting, and Participants  This 12-week randomized clinical trial including men and women aged 18 to 64 years with a body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) of 27 to 43 was conducted on a custom mobile study application. Participants received a Bluetooth scale. Participants lived anywhere in the United States, with a subset of 50 participants living near San Francisco, California, who underwent in-person testing.

Main Outcomes and Measures  The primary outcome was weight loss. Secondary outcomes from the in-person cohort included changes in weight, fat mass, lean mass, fasting insulin, fasting glucose, hemoglobin A1c levels, estimated energy intake, total energy expenditure, and resting energy expenditure.

Results  Overall, 116 participants (mean [SD] age, 46.5 [10.5] years; 70 [60.3%] men) were included in the study. There was a significant decrease in weight in the TRE (−0.94 kg; 95% CI, −1.68 to −0.20; P = .01), but no significant change in the CMT group (−0.68 kg; 95% CI, -1.41 to 0.05, P = .07) or between groups (−0.26 kg; 95% CI, −1.30 to 0.78; P = .63). In the in-person cohort (n = 25 TRE, n = 25 CMT), there was a significant within-group decrease in weight in the TRE group (−1.70 kg; 95% CI, −2.56 to −0.83; P < .001). There was also a significant difference in appendicular lean mass index between groups (−0.16 kg/m2; 95% CI, −0.27 to −0.05; P = .005). There were no significant changes in any of the other secondary outcomes within or between groups. There were no differences in estimated energy intake between groups.

Conclusions and Relevance  Time-restricted eating, in the absence of other interventions, is not more effective in weight loss than eating throughout the day.

Trial Registration  ClinicalTrials.gov Identifiers: NCT03393195 and NCT03637855

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    10 Comments for this article
    A Study that was Poorly Done
    Danielle Hammond |
    16 hours of fasting isn't often enough to lose weight, and the participants were allowed zero calorie beverages. As far as I'm concerned no one should have wasted time and money on this study to try to say that fasting doesn't work.

    Try fasting with only black coffee, tea, or water. And for at least 18-20 hours.
    Have the participants do this for 3 months to become full my adapted. Then present the results.
    No Objective Measure of Compliance and Differential Attrition
    Robert Kaestner, Ph.D. | University
    The study measured compliance through self-reports. According to these self reports, 92.1% complied with CMT and 83.5% complied with TRE.

    Further, it is unclear what non-compliance in the CMT group means? Did it include partial intermittent fasting--e.g., skipping breakfast? Did it mean ever not complying? Or not complying consistently?

    Similar questions apply about compliance for the TRE group? And which group is more likely to misreport compliance?

    The absence of compliance information is potentially quite important. For example, if we scale the weight change of compliers was -1.13 (0.94/0.835) kg. Doing the same for CMT group
    yields -0.74 kg. The difference is -0.39 kg., which is 50% larger than the simple difference reported in Table 2 of article.

    But the absence of accurate and reliable compliance information is a serious flaw that diminishes the value of the results reported in the article.

    Then there is significant attrition and it is non-random by treatment arm. This problem too diminishes the value of the results.

    Overall, this article provides little credible evidence of the effect of intermittent fasting.
    Disease markers?
    Fips Alfredsson, PhD | University of Bogota
    Fasting is not just about weight loss. The study did not measure parameters that could assess general health status, which, in the long run, might be more important than weight loss.
    Apart from this, I find another comment a bit misplaced -- more extreme forms of fasting for much longer times of course will have likely promoted statistically significant differences in weight loss; yet, the idea behind studies like this is that a rhythm of 16:8 is what most people can do it, while 18:6 or 20:4 is much harder to achieve and live by for a broad
    sector of the population, and therefore not very feasible as an intervention method.
    Regardless, it would have been important to consider more measures than weight loss to assess the efficiency of 16:8.
    Time-restricted Eating Misunderstood in Study
    MH Tang, MSc | The study states that 3 meals were consumed - obviously the participants will not loose weight if total caloric intake remains unchanged.
    The study states that 3 meals were consumed - obviously the participants will not loose weight if total caloric intake remains unchanged.
    The study authors have also taken the time-restricted eating out of proper context i.e. time-restriction is to bw seen in the context of not consuming 2 of the typical 3 meals in a day - usually breakfast and lunch is skipped, or just breakfast.
    Why even do such a study without controlling for what a subject eats?
    Rod Erickson, DC, MS | Miramar College
    As long as the subjects eat the SAD (standard American diet) ad libitum but limit it to 8 hrs/day does not suggest anything different from what is already known.
    Everyday American Diet is the Culprit
    Sudah Shaheeb, MD | University
    A clever health care lobbyist made a graph of rate of obesity compared to the increasing number of nutritionists, midlevel providers and diabetologists in the USA. There was a good correlation but does it mean that the rise in the number of professionals is the cause of obesity in the USA ? or does it mean that the uncontrollable rate of obesity gave rise to an increasing number of professionals devoting themselves to nutrition, obesity etc.
    I am a medical anthropologist and as someone has mentioned the problem is the quality of food available for an average American in the
    supermarket. That is why they cannot loose weight.
    If you look at culturally congruent Intermittent fasting as among the people of Okinawa and see the high quality of their food, you would understand why they live longer and why they have lower rates of diabetes and also cancers. Cultural Native Americans throughout the continent have practiced intermittent fasting for centuries and North American Indians are overweight and have high rates of diabetes whereas Indians living in Panama (the Cuna of Cuna Yala) have almost negligible rates of those.
    NEJM 25/12/2019 has a very good article on the biochemistry of the effects of Intermittent fasting which cannot be duplicated by forced ketogenic Diet. I plan to write a blog about this at www.medicoanthropologist.blogspot.com
    Intermittent fasting is beneficial metabolically but not sure of its effect on obese people. Okinawans and all the other Blue Zone people do not look at their nourishment as DIET.
    Whenever possible, please eat FOOD and not manufactured substitute.
    What about circadian rhythm?
    Maria Kravchenko, MD |
    The subjects in the TRE group were allowed to eat until 8 pm. There are many studies looking at the relationship of meal intake to circadian rhythm; these all show that eating later in the day is associated with adverse metabolic effects and weight gain. This study would be stronger if it had compared several groups with different time periods involved.
    An incomplete study
    Shreya Ahana Ayyub, PhD | Max Planck Institute for Biophysical Chemistry
    As the authors cite in their introduction, the ideal TRF model as used in mice, employed an isocaloric high fat diet. In the study performed here, there is no provision for measuring caloric intake, let alone matching caloric intake in the CMT and TRE groups. There is also no account of macronutrients consumed in either group. Since the authors go on to highlight the importance of adequate protein consumption while adhering to a TRE diet, the lack of data on macronutrients consumed is a major shortcoming. Differential uptake of ad libitum snacking is likely to occur in these two comparison groups, with the TRE group more likely to snack due to longer periods of abstaining from food. This is another example of why overall caloric tracking is important before drawing conclusions about the efficacy of TRE. The inclusion of participants of diverse ethnicities is a strength. However, the authors have neither discussed the distribution of races in the two groups, nor addressed how the over-representation of caucasians in the CMT group (64%) might affect the results. Normal range of BMI differs considerably by race and perhaps the effects of TRE do as well. The study does not explore this. The description of BMI, waist-to-hip ratio, waist circumference and fat mass do not include any acknowledgement of differences by sex. Based on the factors I have discussed, the authors cannot unequivocally state that TRE is not effective for weight loss.
    About this study
    Dan Schuyler |
     I have two comments about this study.

    1) It appears the TRE group was not monitored to verify they complied with the TRE requirements.

    “the time-restricted eating (TRE) group was instructed to eat ad libitum from 12:00 pm until 8:00 pm and completely abstain from caloric intake from 8:00 pm until 12:00 pm the following day.”

    If this is indeed the case, then the data reported by the TRE group could potentially be inaccurate.

    2) It would interesting to see a study of a TRE window of 20:4 vs. a TRE window
    of 16:8, as I suspect the results would be different.
    Concerns about the study
    George Chrysochou, M.Sc. |

    There are several issues with this study:

    1. Self-reported "compliance" isn't an objective method to observe compliance.

    2. 18/6 diet is barely enough to trigger changes in insulin resistance ( 23/1 diets are the bare minimum to achieve this).

    3. Zero-caloric drinks were allowed during the fasting window, although they may trigger an insulin response.

    4. The quantity and quality of the food and calories were not controlled as well.