Time-Restricted Eating Tied to Modest Weight Loss

Restricting daily eating to a 10-hour window was no silver bullet for boosting weight loss in people with obesity and prediabetes, a small study found.

In the 12-week trial, both time-restricted eating (TRE) and a usual pattern of eating led to a modest amount of weight loss that was similar, according to Nisa Maruthur, MD, MHS, of Johns Hopkins University in Baltimore, and colleagues.

Weight loss was 2.3 kg with TRE and 2.6 kg with a usual eating pattern -- an average difference of 0.3 kg (95% CI -1.2 to 1.9 kg), reported Maruthur and co-authors in the Annals of Internal Medicine. The findings also were presented at the American College of Physicians meeting in Boston.

Both groups received the same diet prepared by the study kitchen, with baseline calorie needs calculated for each participant. Participants in the TRE group ate only between the hours of 8 a.m. and 6 p.m. and consumed 80% of their calories before 1 p.m. each day. Those in the usual-eating group ate between 8 a.m. and midnight and consumed at least half of their calories after 5 p.m. each day.

"Our results indicate that when food intake is matched across groups and calories are held constant, TRE, as operationalized in our study, does not enhance weight loss," Maruthur and colleagues wrote. "[I]f or when TRE interventions reduce body weight, as seen in several effectiveness trials, one mechanism is likely reduced caloric intake."

In an accompanying editorial, Krista Varady, PhD, and Vanessa Oddo, PhD, both of the University of Illinois Chicago, agreed, saying these findings suggest that TRE as a weight-loss method works "simply via reductions in calorie intake." TRE can be effective for weight loss because it's an easy way to help people eat less and omits the need for calorie counting, they pointed out.

"Many patients stop following standard-care diets (such as daily calorie restriction) because they become frustrated with having to monitor food intake vigilantly each day," the editorialists noted. "Thus, TRE can bypass this requirement simply by allowing participants to 'watch the clock' instead of monitoring calories while still producing weight loss."

Benefits of this strategy include its straightforward nature, its lack of financial barriers, and the fact that people can consume familiar foods, they added.

The findings echoed those seen in a 2022 Chinese trial in which people with obesity who followed an 8-hour time-restricted diet in addition to calorie restriction over 12 months didn't lose a significantly greater amount of weight than those on a calorie-restricted diet alone.

Maruthur's group pointed out that most prior trials involving TRE have typically implemented a shorter window -- usually 8 hours, but some have gone as low as 4 hours -- whereas their study used a 10-hour window.

The trial included 41 adults: 21 in the TRE group and 20 in the usual-eating group. Most were women (93%) and were Black (93%).

At baseline, weight and BMI were 95.6 kg and 34.6, respectively, in the TRE group and 103.7 kg and 37.5 in the usual-eating group. HbA1c was 5.9% in both groups.

Each group received 21 prepared meals each week with the same macro- and micronutrient composition. All participants could consume unlimited calorie-free and caffeine-free beverages that were approved by the study, plus 237 mL of coffee per day, 355 mL of diet soda per day, and one alcoholic drink per day. Participants were told to maintain their usual level of physical activity.

The TRE group trended toward a decline in fasting glucose compared with the usual eating group, but the between-group difference wasn't significant. Similarly, there weren't significant differences noted for homeostatic model assessment for insulin resistance, glucose area under the curve, glycated albumin, blood pressure, or lipids.

Physical activity varied slightly between the groups with the TRE group clocking fewer daily active minutes than the usual-eating pattern group, but that difference also wasn't significant (-34.3 minutes per day, 95% CI -75.3 to 6.8 minutes per day).

The trial was a single-site study with a small sample size of primarily Black women, and its generalizability and power were limited, the researchers acknowledged.

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