Can Early-Day Fasting Significantly Boost Metabolism? - Video

Scientists have investigated whether Time-Restricted Eating (TRE), a dietary pattern limiting food intake to a 10-hour or shorter window daily, enhances metabolic health and insulin sensitivity in women with overweight or obesity. A recent randomized crossover trial published in Science Translational Medicine compared early Time-Restricted Eating (8 am–4 pm) and late Time-Restricted Eating (1 pm–9 pm) under carefully controlled caloric intake to isolate the effects of meal timing from calorie reduction.

Time-Restricted Eating has gained interest for potential benefits in weight management and cardiometabolic health, possibly by aligning eating with circadian rhythms. While animal studies and some human trials have indicated improvements in glucose regulation, lipid levels, and blood pressure, many have lacked rigorous control of calorie intake and physical activity, leading to inconsistent findings. This study uniquely focused on women, an often-underrepresented group, to assess metabolic and circadian responses to Time-Restricted Eating.

Thirty-one women with a mean BMI of 30.5 kg/m² participated in a 10-week crossover design, undergoing two 2-week intervention phases (eTRE and lTRE) separated by washout. Participants maintained their usual diets and activities, consuming food only within the assigned 8-hour window. Insulin sensitivity was measured via oral glucose tolerance tests (OGTT), alongside assessments of body composition, continuous glucose monitoring, blood pressure, lipids, inflammatory markers, appetite hormones, sleep timing, and gene expression related to circadian rhythms. Caloric intake and physical activity were closely monitored and controlled.

Neither early Time-Restricted Eating nor late Time-Restricted Eating significantly improved insulin sensitivity or other key cardiometabolic markers when calorie intake was constant. Both interventions produced modest weight loss (greater in eTRE) and shifts in circadian phase, with late Time-Restricted Eating delaying internal timing by approximately 40 minutes. Hormonal changes affecting appetite were noted, including increased Peptide YY in late Time-Restricted Eating mornings and decreased leptin in both groups. Circadian gene expression was altered, confirming food timing as a modulator of biological rhythms.

These results suggest that metabolic benefits observed in prior Time-Restricted Eating studies likely stem from calorie restriction rather than timing alone. Meal timing influences circadian regulation but may not independently improve insulin sensitivity absent caloric changes. Further long-term trials with diverse populations are needed to clarify Time-Restricted Eating’s role in metabolic health.

REFERENCE: Peters, B., Schwarz, J., Schuppelius, B., Ottawa, A., Koppold, D.A., Weber, D., Steckhan, N., Mai, K., Grune, T., Pfeiffer, A.F.H., Michalsen, A., Kramer, A., Pivovarova-Ramich, O. (2025). Intended isocaloric time-restricted eating shifts circadian clocks but does not improve cardiometabolic health in women with overweight. Science Translational Medicine, 17(822). DOI: 10.1126/scitranslmed.adv6787.