Effect of weight loss on maximal fat oxidation rate in obese men

SummaryIntroduction: The hallmark features of obesity include insulin resistance and an impaired ability to oxidize lipids. As compared to exercise training, it remains relatively unclear if diet-induced weight loss can also induce fat metabolism. This study was undertaken to examine the effects of diet-induced weight loss on fat metabolism during a single session of exercise in middle-aged obese men. Methods: Fifteen obese men who were otherwise healthy (average age of 53.5 ± 6.9 yr and average body mass index of 27.8 ± 1.6 kg/m2) participated in a 12-wk weight loss program primarily consisting of dietary modification. Maximal fat oxidation (MFO) rates, MFO per lean body mass (MFOLBM) and insulin resistance (HOMA-IR) were measured before and after the program. Participants performed a 24-min graded exercise test on a cycle ergometer, with 15-W increments every 4 min. Expired gas analysis was performed by indirect calorimetry, and nonprotein respiratory quotient equations were used to calculate fat oxidation rates. Results: The weight (−8.3 ± 3.8 kg), fat mass (−4.5 ± 1.9 kg), and lean body mass (−3.8 ± 2.4 kg) (P < 0.001 for all measurements) of the participants were decreased at the end of the 12-wk program. The MFO tended to increase by 19% (P = 0.08) and MFOLBM significantly increased by 28.8% (P = 0.02). Although insulin resistance also significantly decreased by 49% (P < 0.001), changes in fat oxidation variables did not correlate with changes in insulin resistance. Conclusion: Diet-induced weight loss improves fat metabolism with the improvement in insulin resistance.