Time-restricted eating does not confer ‘clinically significant’ weight loss in obesity
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Time-restricted eating interventions, especially those with an eating window of 8 hours or longer, are not associated with weight loss of 5% or greater for most adults with obesity, according to a speaker.
In a presentation analyzing time-restricted eating randomized controlled trials at the World Congress on Insulin Resistance, Diabetes & Cardiovascular Disease, Max Petersen, MD, PhD, a fellow in the division of endocrinology, metabolism and lipid research and the Center for Human Nutrition at Washington University School of Medicine in St. Louis, discussed how previous research in rodents found time-restricted eating was capable of preventing and treating obesity and other metabolic diseases. However, similar findings have not been observed in most human studies, due in part to physiological differences between rodents and humans, a potential lack of compliance in people and the diets used in rodent studies.
“We now have enough randomized controlled trial data to have a fair idea of the effects of time-restricted eating on weight and metabolic outcomes in people with overweight or obesity without diabetes,” Petersen told Healio. “The most common time-restricted eating window length is 8 hours and is sometimes called the 16:8 diet. This form of time-restricted eating, by itself, generates less than 5% weight loss on average — not enough to generate significant improvements in cardiometabolic health.”
A plethora of time-restricted eating patterns have been analyzed in clinical trials, according to Petersen. The eating windows in these trials range from as many as 12 hours to as few as 4 hours. Some of the shorter time-restricted eating windows of 4 to 8 hours include early time-restricted eating, where evening meals are skipped, and late time-restricted eating, where breakfast is skipped.
Weight loss minimal with 8-hour eating window
The most common time-restricted eating window analyzed in trials was an 8-hour eating window duration with 16 hours of fasting. Petersen noted while many studies have analyzed 8-hour time-restricted eating, few studies have analyzed the pattern on its own without any other diet changes or intervention. For one study published in JAMA Internal Medicine, researchers randomly assigned 116 adults to 8 hours of time-restricted eating or placebo, with no other dietary changes or interventions. The study found no difference in weight loss, fasting glucose, fasting insulin, plasma triglycerides or systolic blood pressure between the intervention and control groups.
Two trials that analyzed an early 8-hour time-restricted eating window added to a calorie-restricted diet found a minimal difference in weight loss. In one trial, adults randomly assigned to time-restricted eating with caloric restriction lost less than 2% more weight than adults eating a calorie-restricted diet alone at 14 weeks. Another trial conducted in China found no difference between the time-restricted eating with caloric restriction and control groups at 6 months and 1 year.
In an analysis of randomized controlled trials evaluating time-restricted eating with a duration of 4 weeks or more, Petersen said there is a correlation between the eating window duration and the percentage of weight lost. In three randomized controlled trials that analyzed a time-restricted eating window of 4 to 6 hours, participants randomly assigned to time-restricted eating had a 3% greater mean body weight loss and a 10 to 20% greater decrease in fasting insulin compared with controls.
“In none of these trials is there more than a 5% weight loss between time-restricted eating and control groups,” Petersen said during the presentation. “That 5% threshold in obesity without diabetes is generally considered clinically significant weight loss. With that in mind, it’s not surprising to see that, when we consider the metabolic outcomes in randomized controlled trials, the results are mostly null.”
Greater loss with other obesity pharmacotherapies, interventions
When compared with other trials evaluating the efficacy of obesity pharmacotherapies, bariatric surgery, and lifestyle interventions, Petersen said there are many options that confer greater weight loss in adults with obesity than time-restricted eating.
“There is certainly variability among study participants and some individuals may achieve clinically significant weight loss with time-restricted eating,” Petersen told Healio. “But on average, people with obesity can expect less weight loss with time-restricted eating than with intensive lifestyle interventions or modern pharmacologic obesity therapies. It is also not clear from published randomized controlled trial data that there are any important weight-independent metabolic benefits of time-restricted eating.”
Petersen said ongoing studies are examining whether time-restricted eating has metabolic effects independent of weight loss and why some people are more likely to achieve a greater than 5% weight loss than others. He added that some research has found that time-restricted eating may be able to improve glycemic control in people with type 2 diabetes and more studies should further investigate that possible association.
References:
- Jamshed H, et al. JAMA Intern Med. 2022;doi:10.1001/jamainternmed.2022.3050.
- Liu D, et al. N Engl J Med. 2022;doi:10.1056/NEJMoa2114833.
- Lowe DA, et al. JAMA Intern Med. 2020;doi:10.1001/jamainternmed.2020.4153.
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Petersen M. Session 21: Clinical efficacy of time-restricted eating in people: hope or hype? Presented at: World Congress on Insulin Resistance, Diabetes & Cardiovascular Disease; Dec. 1-3, 2022; Universal City, California (hybrid meeting).
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