Diurnal differences in postprandial glucose and triglyceride metabolism reveal metabolic flexibility and resilience.

Abstract

Objective The study investigated the diurnal variance in metabolic resilience (i.e., the robustness, the recovery and re-orientation of metabolism) and metabolic flexibility in glucose and fat oxidation rates to three identical test meals. Methods Eight young, healthy subjects consumed identical liquid mixed meals three times a day (33 % of energy requirement each), followed by a defined bout of physical activity conducted in a whole-room indirect calorimeter to continuously assess energy expenditure and postprandial changes in substrate oxidation rates, as a measure of metabolic flexibility. A mathematical metabolic resilience model was used to analyze the postprandial blood parameters. Results Throughout the day, postprandial glucose area under the curve (AUC) increased (breakfast mean ±SD 17.3 ±2.4 vs. dinner 20.8 ±2.0 g/180min; p<0.001) while triglyceride AUC decreased (breakfast 434 ±158 vs. dinner 365 ±104 mg/180min; p=0.039) at identical insulin AUC and energy balance. Fat oxidation increased from breakfast 24.8 ±8.7 to dinner 28.0 ±8.7 g/180min (p=0.029), while respiratory exchange ratio declined from 0.035 ±0.026 to 0.012 ±0.029 (p=0.005). Metabolic resilience model reveals a diurnal increased rate of lipolysis of circulating triglycerides at a concomitant decrease in the rate of exogenous and endogenous triglyceride appearance. Conclusion Meal-to-meal changes in glucose AUC indicate rising insulin resistance during the day. However, this reflects a resilient metabolism that shifts to triglyceride metabolism in the evening while maintaining insulin AUC and energy balance.