Delaying mealtimes reduces fat oxidation: A randomized, crossover, controlled feeding study.

Abstract

This study investigated the effects of circadian misalignment (CM), induced by delaying mealtimes, independent of sleep timing and duration and eating window duration, on energy expenditure (EE), respiratory quotient (RQ), and substrate oxidation. Healthy adults, aged 20 to 49 years, participated in this randomized crossover study under controlled feeding conditions. Eating window duration was identical in both conditions (circadian alignment [CA]: 9:00 am-7:00 pm; CM: 1:00 pm-11:00 pm), and bedtimes were constant (11:30 pm-8:00 am). EE, RQ, and substrate oxidation were obtained over 23 hours in a metabolic chamber on days 3 and 4 and days 14 and 15 in each condition. Twenty-four-hour and post-meal outcomes were analyzed using a linear mixed-effects model including condition, day, and day-by-condition interaction as main predictors and sex as a covariate. Three men and four women (age 37.4 ± 8.8 years, BMI 30.4 ± 3.3 kg/m2 ) completed the study. Twenty-four-hour EE did not differ between conditions. Post-meal RQ for dinner and snack was higher in CM versus CA (both p< 0.001) with correspondingly higher glucose oxidation (both p< 0.01) and lower fat oxidation (dinner only p= 0.0001). CM, induced by delaying mealtimes by 4 hours relative to CA, independently shifts nutrient metabolism toward greater carbohydrate and lower fat oxidation.