Intended Isocaloric Time-Restricted Eating Shifts Circadian Clocks but Does Not Improve Cardiometabolic Health in Women with Overweight

Time-restricted eating (TRE) is a promising strategy to improve metabolic outcomes. However, it remains unclear whether TRE has cardiometabolic benefits in an isocaloric setting and whether its effects depend on the eating timing. We conducted a randomized cross-over trial to directly compare the effects of a two-week early TRE (eTRE: eating between 8:00 and 16:00 hr) and a two-week late TRE (lTRE: eating between 13:00 and 21:00 hr) on insulin sensitivity, cardiometabolic risk factors, and the internal circadian phase. During the restricted 8-hour eating period, participants were asked to consume their habitual food quality and quantity. In 31 women with overweight or obesity, insulin sensitivity did not differ between (-0.07; 95% CI, -0.77 to 0.62, P = 0.60) and within (eTRE: 0.31; 95% CI, -0.14 to 0.76, P = 0.11; lTRE: 0.19; 95% CI, -0.22 to 0.60, P = 0.25) interventions. 24-hour glucose, lipid, inflammatory, and oxidative stress markers showed no clinically meaningful between- and within-intervention differences. Participants demonstrated high timely adherence (eTRE: 96.5%, lTRE: 97.7%), unchanged dietary composition and physical activity, minor daily calorie deficit (eTRE: -167 kcal/day) and weight loss (eTRE: -1.08 kg, lTRE: -0.44 kg). lTRE delayed the circadian phase in blood monocytes (24 min; 95% CI, -5 to 54 min, P = 0.10) and sleep midpoint (15 min; 95% CI, 7 to 22 min, P = 0.001) compared to eTRE. Overall, in an intended isocaloric setting, neither eTRE nor lTRE improve insulin sensitivity or other cardiometabolic traits despite a shift of internal circadian clocks.