Timing Matters: Diurnal Variation of Maximal Fat Oxidation and Substrate Oxidation Rates in Metabolic Syndrome – A Randomized Crossover Study

Abstract

Abstract Purpose: The primary aim of this study was to investigate if diurnal oscillation in maximal fat oxidation and substrate oxidation rates during exercise exists in subjects with Metabolic syndrome. Methods: In a randomized crossover design, 14 MetS patients were assigned to two graded exercise tests conditions performed in the morning (between 7:00 and 9:00 a.m) and in the afternoon (between 4:00 and 5:00 p.m). Results: MFO increased by 20.56 % from morning to afternoon (time of day, p=0.0002, η2p = 0,69) and this was independent of gender (gender*time of day, p=0.144), indicating that MFO was higher in the afternoon than in the morning in both males (11.04 %) and females (38.82%). There was a significant time of day effect in Fatox rates, (p<0.0001, η2p = 0,81) and intensity (p=0.004, η2p = 0,469) that was independent of gender (time of day*intensity*gender interaction, p=0.0164) indicating that Fatox was higher in the afternoon than in the morning in both male and females Conclusion: Our study extends previous findings on the existence of diurnal variation in maximal fat oxidation to MetS patients, highlighting the afternoon as a more favorable time for fat utilization during exercise, and shows that gender does not interfere with these diurnal variations as previously suggested. These findings have practical implications for optimizing training strategies in MetS patients. Further research is needed to delineate the discrepancy between gender and substrate oxidation patterns. Trial Registration number: PACTR202306776991260