The 8-hour eating window for weight loss has emerged, but the full picture is more complex

Data collected from five trials put the duration of the eating window under the microscope, testing whether the number of hours people eat each day affects weight and metabolic health.

He studies: A shorter eating window than time-restricted eating is more beneficial for weight loss: pooled analysis of individual data from five trials. Image credit: Ahmet Misirligül/Shutterstock

In a recent study published in the magazine Nutrition and diabetesThe researchers examined associations between time-restricted eating at different times (three) Window periods, changes in body weight, and cardiometabolic outcomes.

TRE is a type of intermittent fasting where the eating period is limited to 4-12 hours per day. Traditional weight loss approaches often involve counting calories and restricting certain foods, while TRE does not typically describe nutritional composition or calories. Individuals adhering to TRE typically reduce their caloric intake by approximately 200 to 500. Kcal/day and lose about 1% to 5% of their initial weight.

A recent Cochrane meta-analysis found little difference in weight loss between conventional dietary approaches and intermittent fasting (including TRE), although the certainty of the evidence was low. In comparison, meta-analyses that focused only on TRE interventions report a reduction in body weight. Studies have also reported mixed effects of TRE on cardiometabolic outcomes. TRE windows vary widely across studies; As such, the optimal number of eating/fasting hours remains unclear.

About the study

In this study, researchers examined associations between different TRE windows and body weight and cardiometabolic outcomes, including blood pressure (baby), fasting plasma glucose (FPG), and lipid profile. They performed a pooled analysis of individual data from five TRE trials. Three of them were single-arm, and two of them had randomized controls, so the eating window groups were not randomized head-to-head. All trials recruited adults with a habitual eating window of at least 14 hours per day and at least one metabolic syndrome component.

Participants assigned to TRE set their eating windows to 8, 10, or 12 hours, without any restrictions on energy intake or diet quality. The controls maintained their habit At will eat, receive nutritional counseling, or have been given guidance on healthy eating. The trials lasted three to six months and were conducted in the United States (three) and Europe (two). Participants used a mobile phone application to record their daily food and beverage intake. Blood pressure and body weight were measured.

FPG, triglycerides, high-density lipoprotein – cholesterol (HDL-C) Levels were measured; Low-density lipoprotein – cholesterol (LDL-C) were calculated using the Friedewald equation in four of the five studies. The primary outcome of the study was the change in body weight from baseline in kilograms and as a percentage of initial body weight. Secondary outcomes included BP, FPG, and lipid profile (HDL-C, LDL-C, and triglycerides).

Linear regression was performed to examine associations between TRE interventions and primary and secondary outcomes, using eating windows assigned during the intervention, actual eating windows measured during follow-up (as a proxy for adherence to TRE or control conditions), and changes in eating windows between the pre- and post-intervention periods. Models were adjusted for sex, age, and baseline BMI (Body mass index).

Results

The study included 124 participants, with an average age of 47 years and a baseline eating window of 15 hours. Most participants were female (67%) and assigned to TRE (77%). The TRE groups included 11, 59, and 25 participants assigned to the 8-, 10-, and 12-hour TRE regimens, respectively. On average, participants assigned to TRE reduced their eating window by about four hours and lost 2.18 kg of body weight compared to baseline.

Controls did not significantly reduce the eating window or body weight. Participants assigned to the 8-hour TRE lost more weight than those assigned to the 12-hour TRE or the control group, although the difference compared with the 10-hour TRE was not statistically significant. This pattern generally persisted after adjusting for baseline BMI, age, and sex. Actual eating window analysis indicated that shorter windows were associated with greater weight loss after the intervention, but adjustment for age, sex, and baseline BMI moderated the association.

Greater reductions in the eating window during TRE were also associated with greater weight loss at the end of the intervention, after adjusting for the baseline eating window. The relationship weakened after adjusting for sex, age, and baseline BMI. Participants in the 10-hour TRE had greater reductions in systolic blood pressure than those who underwent the 12-hour TRE. There were no other significant differences in BP, FPG, or lipid profile by the duration of the allocated eating window. These results were also not related to the actual duration of the eating window or changes in the eating window. Most participants did not have diabetes and had normal fasting glucose levels, which may limit the ability to detect improvements in glucose levels.

Conclusions

Taken together, 8-hour TRE was associated with greater weight loss than 12-hour TRE and the control group; The 10-hour comparison was not statistically significant. Larger reductions in habitual eating intervals were also associated with greater weight loss, but this relationship weakened after adjustment. TRE duration showed no consistent relationship with lipid profile, BP or FPG.

Study limitations include small sample size, small number of trials, small study groups, heterogeneity between studies, follow-up of up to 6 months, lack of caloric intake, lack of eating windows of less than 8 hours, and lack of adjustment for multiple comparisons. Race and ethnicity were not included as covariates because they were not collected consistently across studies. Further studies with longer follow-up periods, more diverse populations, and a wider range of TRE windows are needed.