Intermittent fasting has become a popular approach for weight control. Some people see this as fasting for a few days a week and eating on the others. Another approach, however, is to practice time-restricted eating. You would limit meals to certain hours of the day and make sure that you spend at least 12 hours and preferably longer consuming no calories. Scientists have noted a number of potential benefits from adhering to this sort of biological clock (Annual Review of Nutrition, Aug. 21, 2019). The only problem is that there have not been many well-controlled trials of this eating strategy for weight loss.
Review of Time-Restricted Eating Studies:
A recent review concludes that limiting eating to 8 to 10 hours of the day can help people lose weight. In addition, this tactic can improve their metabolic health (Endocrine Reviews, Sep. 22, 2021). The authors suggest that paying attention to the clock is easier (and more effective) than counting calories. They recommend, however, that the hours for eating be consistent day after day. What follows automatically from such a regimen is intermittent fasting for at least 14 hours out of 24.
One of the scientists notes:
“Intermittent fasting can improve sleep and a person’s quality of life as well as reduce the risk of obesity, diabetes and heart disease.”
Can Time-Restricted Eating Make Weight Loss Easier?
However, a study published in JAMA Internal Medicine threw the idea of time-restricted eating into question (JAMA Internal Medicine, Nov. 2020). Investigators at the University of California, San Francisco, recruited 141 overweight people to participate in a controlled trial. Our of those, 105 completed the three-month study.
How the Study Worked:
The researchers randomly assigned the volunteers to time-restricted eating or continuous meal timing. In other words, one group could eat as they normally did (CMT), while the intervention group ate nothing before noon or after 8:00 o’clock in the evening. Consequently, the intervention group fasted for 16 hours a day.
Sadly, the results were underwhelming. The time-restricted eating group lost roughly 2 to 3 pounds by the end of 12 weeks. (That was statistically significant, though not impressive.) The control group shed about one and a half pounds during the same period of time. That difference is not statistically significant. Nor could the researchers detect differences between the two groups in estimated energy intake.
Interestingly, the weight that was shed in the intermittent fasting group was more muscle than fat. The lead author was surprised by these results, which confirm the need for placebo-controlled trials. He had anticipated that intermittent fasting would give people an advantage in their weight-loss efforts.
Would an Earlier Eating Period Perform Better?
Critics may complain that the time frame this study used may have contributed to the disappointing results. They suggest that time-restricted eating might be more effective earlier in the day. We won’t know if that hypothesis is true unless another group conducts a properly controlled trial like this one, but restricting eating to, say, 6 am to 2 pm or 8 am to 4 pm.
Time-Restricted Eating for Elite Cyclists:
One such study has been published, although it is quite small (Journal of the International Society of Sports Nutrition, Dec. 11, 2020). Sixteen elite young cyclists participated in a time-restricted eating trial during a month when they were training hard. The group randomly assigned to restricted hours consumed all their meals between 10 am and 6 pm. The other group ate any time between 7 am and 9 pm. Remember, all of these volunteers were exercising like crazy the whole time. The scientists found that the dietary intervention promoted weight loss (fat only) and improved some metabolic markers. There were no noticeable advantages in cycling performance, but the restrictions on meals appear to reduce inflammation.
We have interviewed experts on chronobiology and time-restricted eating. If the topic interests you, you might listen to Show 1143: Can You Control Your Blood Sugar by Fasting? with Dr. Jason Fung. Dr. Marie-Pierre St. Onge also discussed this idea in Show 1094: Does It Matter When You Eat?