Meal timing affects glucose tolerance, substrate oxidation and circadian-related variables: A randomized, crossover trial

BACKGROUND/OBJECTIVES: Timing of food intake associates with body weight regulation, insulin sensitivity and glucose tolerance. However, the mechanism is unknown. The aim of this study was to investigate the effects of changes in meal timing on energy-expenditure, glucose-tolerance and circadian-related variables. SUBJECTS/METHODS: Thirty-two women (aged 24 +/- 4 years and body mass index 22.9 +/- 2.6 kg m(-2)) completed two randomized, crossover protocols: one protocol (P1) including assessment of resting-energy expenditure (indirect-calorimetry) and glucose tolerance (mixed-meal test) (n = 10), the other (P2) including circadian-related measurements based on profiles in salivary cortisol and wrist temperature (T-wrist) (n = 22). In each protocol, participants were provided with standardized meals (breakfast, lunch and dinner) during the two meal intervention weeks and were studied under two lunch-eating conditions: Early Eating (EE; lunch at 13:00) and Late Eating (LE; lunch 16:30). RESULTS: LE, as compared with EE, resulted in decreased pre-meal resting-energy expenditure (P = 0.048), a lower pre-meal protein-corrected respiratory quotient (CRQ) and a changed post-meal profile of CRQ (P = 0.019). These changes reflected a significantly lower pre-meal utilization of carbohydrates in LE versus EE (P = 0.006). LE also increased glucose area under curve above baseline by 46%, demonstrating decreased glucose tolerance (P = 0.002). Changes in the daily profile of cortisol and T-wrist were also found with LE blunting the cortisol profile, with lower morning and afternoon values, and suppressing the postprandial T-wrist peak (P < 0.05). CONCLUSIONS: Eating late is associated with decreased resting-energy expenditure, decreased fasting carbohydrate oxidation, decreased glucose tolerance, blunted daily profile in free cortisol concentrations and decreased thermal effect of food on T-wrist. These results may be implicated in the differential effects of meal timing on metabolic health.