Caloric intake may be more important for weight loss than meal timing, study suggests

Key takeaways:

• Time-restricted eating was linked to similar reductions in weight compared with usual eating patterns.
• Time-restricted eating may still benefit patients by decreasing their caloric intake, researchers said.

BOSTON — Time-restricted eating did not result in more weight loss vs. a usual eating pattern, suggesting that overall caloric intake may have a larger effect on weight loss than meal timing, researchers reported.

The findings were presented during the plenary session at the ACP Internal Medicine Meeting and simultaneously published in Annals of Internal Medicine.

“We feel that clinicians can counsel their patients that [time-restricted eating (TRE)] may help them to lose weight, but likely because of a decrease in caloric intake,” Nisa M. Maruthur, MD, MHS, FACP, an associate professor at Johns Hopkins Bloomberg School of Public Health, said during the presentation.

According to Maruthur and colleagues, prior studies on TRE have showed beneficial effects on weight and cardiometabolic outcomes, although “the effects of TRE vs. other changes in behavior on outcomes are difficult to isolate in these studies given that most have not used a controlled feeding design.”

The researchers conducted an isocaloric feeding study to investigate the effects of TRE among 41 participants (mean age, 59 years; 93% women) with obesity and either prediabetes or diet-controlled diabetes. They randomly assigned participants in a 1:1 ratio to:

• TRE, which included a 10-hour eating window between 8 a.m. and 6 p.m.; or
• a usual eating pattern (UEP), which included an eating window of 16 hours or fewer between 8 a.m. and midnight.

Participants in the TRE group consumed 80% of their calories by 1 p.m., whereas participants in the UEP group consumed 50% or more of their calories by 5 p.m.

In both groups, participants received prepared meals with identical micronutrient and macronutrient compositions in addition to instructions on when to consume the meals over 12 weeks.

At baseline, the TRE group and UEP group had a mean weight of 95.6 kg (95% CI, 89.6-101.6) and 103.7 kg (95% CI, 95.3-112), respectively.

Maruthur and colleagues found that at 12 weeks, weight decreased by 2.3 kg (95% CI, 1-3.5) in the TRE group and 2.6 kg (95% CI, 1.5-3.7) in the UEP group, for an average difference of 0.3 kg (95% CI, –1.2 to 1.9).

“You can see weight decreased in both arms,” Maruthur said. “So, TRE did not have a benefit over usual eating.”

There were no significant differences between the groups in fasting glucose, BP, waist circumference or lipid levels.

Maruthur noted that, although physical activity “was not one of our main outcomes,” TRE participants had decreased daily activity counts and time spent being active.

A potential explanation behind the findings “is that TRE does not cause weight loss in the setting of isocaloric intake in humans,” Maruthur and colleagues wrote. “Therefore, if or when TRE interventions reduce body weight, as seen in several effectiveness trials, one mechanism is likely reduced caloric intake.”

Maruthur highlighted several limitations of the study. For example, it was conducted at a single site, the results only apply to adults with obesity and prediabetes and “we were not powered to find differences in weight [smaller] than more than 2 kg between arms,” she said.

“We do think that further high-quality research is needed to understand the impact of TRE on physical activity,” Maruthur concluded.

In a related editorial, Krista A. Varady, PhD, a professor of nutrition at the University of Illinois in Chicago, and Vanessa M. Oddo, PhD, an assistant professor of kinesiology and nutrition at the same institution, noted that although TRE “is no more effective than other diet interventions for weight reduction, it offers patients a simplified approach to treating obesity by omitting the need for calorie counting.”

“Moreover, TRE does not require the purchase of expensive food products and allows a person to continue consuming familiar foods, making it a highly accessible diet for lower-resource populations,” they wrote.

References:

• Maruthur NM, et al. Ann Intern Med. 2024;doi:10.7326/M23-3132.
• Maruthur NM, et al. New in Annals of Internal Medicine: Hear it first from the authors. Presented at: ACP Internal Medicine Meeting; April 18-20, 2024; Boston.
• Varady K, Oddo V. Ann Intern Med. 2024;doi:10.7326/M24-0695.