Exercise Fat Oxidation Capacity Is Directly Associated with Body Fatness in Men with Obesity

Abstract

Background: A decreased fat oxidation capacity, called metabolic in flexibility, is liked to obesity and metabolic syndrome. However, evi dence supporting this paradigm is not consistent across literature,partly due to different fat oxidation capacity indicators used among studies. This study aimed to determine the independent interrelation of body fatness with the following metabolic flexibility markers measured during submaximal exercise: 1) maximal fat oxidation (MFO); 2) total fat oxidation (TFO), 3) maximum respiratory exchange ratio (RERpeak). Methods: The cardiorespiratory fitness (CRF), MFO, and its corresponding intensity (FATmax) were defined through a graded exercise test on 21 men with obesity (95% CI: 32.0-39.5% body fat). Seven days after, all subjects walked for 60 min at FATmax, and the resulting TFO and RERpeak were recorded. Gas exchange, blood lactate, and heart rate levels were measured during the graded and steady-state exercise trials. Multivariate analysis of variance and multiple regression were used to investigate the independent relationship of body mass index (BMI), body fat percentage (BF%), and CRF on Metflex markers. kgFFM-1·min-1) Results: The MFO (4.14 ± 1.24 mg occurred at a low exercise intensity (35.85 ± 6.09% of VO2peak) during the graded exercise test. The RERpeak (0.92 0.03) occurred after 15 min of walking at FATmax, and 60-min TFO was 136.95 ± 12.88 mg·kgFF M- 1·h-1. Together, CRF and %BF explained 40% and 31% of RERpeak and TFO variance respectively (p < 0.01). Otherwise, only %BF was R2 directly associated with MFO ( = 0.40, p < 0.01). Conclusions: Fat oxidation increase in response to physical exercise is positively related to body fatness in men with obesity.