Trial Examines Time-Restricted Eating vs Calorie Restriction over 12 Months for Weight Loss

A new study, published in the New England Journal of Medicine, provides evidence detailing the apparent lack of benefit seen with time-restricted eating against daily calorie restriction in individuals with obesity for weight loss goals.

A randomized clinical trial of 139 patients followed for 12 months, results of the trial suggest those with time-restricted eating with calorie restriction experienced nearly 2 kilograms more weight loss than those with calorie restriction alone, but the magnitude of this effect failed to reach statistical significance.

“Our trial showed that the two diet regimens had similar effects on weight loss and that it was feasible for participants to adhere to their assigned calorie intake restrictions. Consistent with the findings in previous studies, our data suggest that caloric intake restriction explained most of the beneficial effects of a time-restricted eating regimen,” wrote investigators. “However, our results support a strategy of time-restricted eating combined with caloric intake restriction (prescribed according to current dietary guidelines) as a viable and sustainable approach for obesity management.”

Although they have always played an integral role, dietary science and nutrition have become a focal point in preventive medicine in recent years. Among the topics of discussion when examining these subjects is the efficacy of different dietary approaches, including time-restricted eating. Despite the increased interest in the subject, few randomized clinical trials have assessed or compared the effects of dietary approaches.

With this in mind, a team from the Nanfang Hospital at the South Medical University in Guangzhou China and the Department of Epidemiology at the Tulane University School of Public Health and Tropical Medicine randomized a cohort of 139 patients with obesity to time-restricted eating with calorie restriction or daily calorie restriction alone. These patients were followed for 12 months and instructed to follow a calorie-restricted diet of 1500-1800 calories per day for men and 1200-1500 calories per day for women.

The primary outcome of interest was the difference between the groups in observed change from baseline to end of study in body weight. Secondary outcomes of interest included changes in waist circumference, body-mass index (BMI), amount of body fat, and measures of metabolic risk factors. Of note, those randomized to Time-restricted eating were instructed to eat only between 8:00 a.m. and 4:00 p.m.

Participants for the study were recruited from the general public in Guangzhou, China and were considered eligible if they were 18-75 years of age and had a BMI of 28-45 kg/m2. Participants were considered ineligible based on presence of acute or chronic viral hepatitis, malignant tumors, diabetes, serious liver dysfunction or chronic kidney disease, current smoking, serious cardiovascular or cerebrovascular disease within 6 months before randomization, severe gastrointestinal diseases or gastrointestinal surgery in the 12 months before randomization, active participation in a weight-loss program, use of medications that affect weight or energy balance, and current or planned pregnancy.

Of the 139 patients who underwent randomization from November 30, 2018-July 28, 2021, 69 were randomized to time-restricted eating and 70 were randomized to calorie-restriction only. The overall study cohort had a mean age of 31.9±9.1 years and a mean weight of 88.2±11.6 kg at baseline. Of the 139 participants who underwent randomization, 135 completed the 6-month intervention and 118 completed the 12-month intervention.

Upon analysis, results of the trial suggested the mean weight loss from baseline to 12 months was -8.0 kg (95% CI, -9.6 to -6.4) in the time-restriction group and −6.3 kg (95% CI, -7.8 to -4.7) in the daily-calorie-restriction group, yielding a non-significant difference between the study arms (net difference, 1.8 kg [95% CI, -4.0 to 0.4]; P=.11). Further analysis indicated the effects of each approach on waist circumferences, BMI, body fat, body lean mass, blood pressure, and metabolic risk factors were consistent with the results of the primary outcome. Investigators also pointed out no substantial differences were observed between the study arms when assessing incidence of adverse events.

In their conclusion, investigators cautioned clinicians to consider the limitations of their trial before extrapolating results into their own patient populations. These limitations include an inability to generalize results to other patient populations, to different periods of time-restricted eating, or to those of other races or ethnic groups. Investigators also noted measurements of total energy expenditure and physical activity were not controlled for in the trial.

In an editorial, Blandine Laferrère, MD, PhD, of the Columbia University Irving Medical Center, and Satchidananda Panda, PhD, of the Salk Institute for Biological Studies, underlined the importance of considering limitations within the trial before interpreting results, but also underlined the importance of the results in setting benchmarks for future research into dietary interventions.

"Despite these limitations, this trial offers an important benchmark for a dietary lifestyle intervention that combines quality, quantity, and timing of nutrition, and it shows the evolving use of digital platforms that incorporate self-monitoring by patients and frequent feedback to deliver the intervention,” wrote Laferrère and Panda.

This study, “Calorie Restriction with or without Time-Restricted Eating in Weight Loss,” was published in the New England Journal of Medicine.