September 27, 2021
Time-restricted eating — where caloric intake is restricted within a consistent interval of less than 12 hours without overtly attempting to reduce calories — has "generated impressive [animal] data in preventing or reversing metabolic diseases associated with obesity," and "more rigorous human studies are needed," conclude the authors of a new review.
"Time-restricted eating is an easy-to-follow and effective dietary strategy that requires less mental math than counting calories," said senior author Satchidananda Panda, PhD, of the Panda Lab at the Salk Institute for Biological Studies, La Jolla, California.
"People who are trying to lose weight and live a healthier lifestyle should pay more attention to when they eat as well as what they eat," Panda advised.
Moreover, "eating at random times breaks the synchrony of our internal program [circadian clock] and make us prone to diseases," so it is important to eat at consistent times.
Furthermore, time-restricted eating, a type of intermittent fasting, "is a lifestyle that anyone can adopt," he noted, which "can help eliminate health disparities and lets everyone live a healthy and fulfilling life."
The article, by Emily N. Manoogian, PhD, a postdoctoral fellow in the same lab, and colleagues was published online September 22 in Endocrine Reviews.
The authors suggest that healthcare providers should encourage high-risk patients (such as those with obesity) to monitor their eating and sleeping times and make easy-to-implement behavior changes, such as decreasing after-dinner snacking and going to bed at the same time each day.
Animal Experiments, Early Studies in Humans
In animal experiments, time-restricted feeding without reducing caloric intake prevented or attenuated the severity of metabolic diseases including obesity, glucose intolerance, hepatic steatosis, dyslipidemia, and age-related decline in cardiac function, Manoogian and colleagues report.
In pilot human studies, time-restricted eating with or without explicit calorie reduction was associated with reductions in body weight, glucose intolerance, hypertension, and dyslipidemia.
Most studies did not restrict calories or provide dietary recommendations, yet participants commonly reduced their caloric intake by 7% to 22%.
39 Published Clinical Trials, Many Upcoming Ones
The authors identified 39 clinical trials of time-restricted eating, which were mostly published in the past 2 years, with the earliest one published in 2013.
Most studies were short and small (4 to 12 weeks, 10 to 20 participants) and were of people with obesity, healthy adults, and athletes. Most of the trials had an 8- to 10-hour daily "eating window."
Body weight decreased in 24 of 39 studies, and "importantly," time-restricted eating was feasible and safe in all studies, the authors note.
"Larger randomized control trials are needed as many of the studies to date are smaller pre-post or crossover trials," Manoogian and colleagues summarize. "Yet, the replication of findings, even in diverse patient populations, speak to the potential impact of [time-restricted eating] as a health intervention."
The many ongoing international clinical trials of time-restricted eating that are listed on clinicaltrials.gov should improve our understanding of time-restricted eating, they add.
Some of the larger trials are in participants with prediabetes (344 participants, NCT03504683), diabetes (144 participants, NCT04155619), metabolic syndrome (118 participants, NCT04057339), and firefighters on 24-hour shifts (150 participants, NCT03533023). There are also smaller pilot studies in participants with cancer (NCT04243512) and polycystic ovary syndrome (NCT03792282).
Be Consistent, Do Not Eat Within 3 Hours of Bedtime
In the meantime, the review authors offer the following tips:
- Because high melatonin levels (late at night or early morning) can inhibit proper response to food, choose a time to eat that starts at least an hour after waking and stops at least 3 hours before bedtime. If you sleep 8 hours, that leaves 12 hours for the time-restricted eating window.
- Try to eat within the same time window each day.
- Some research suggests eating earlier in the eating phase is better than eating later.
The study received funding from the National Institute of Diabetes and Digestive and Kidney Diseases, the National Institute on Aging, the National Cancer Institute, the Larry l. Hillblom Foundation, the Wu Tsai Human Performance Alliance, the US Department of Defense, and the Federal Emergency Management Agency. Panda has reported receiving royalties from his book, The Circadian Code. The other authors have reported no relevant financial disclosures.
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