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

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.

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/m(2)) 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.

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.

Diet-induced weight loss improves fat metabolism with the improvement in insulin resistance.: