Is body fat loss a determinant factor in the improvement of carbohydrate and lipid metabolism following aerobic exercise training in obese women?

Thirty-one obese, premenopausal women aged 35.4 ± 5.1 (SD) years exercised for 90 minutes at approximately 55% of maximal aerobic power (V̊o2max) four to five times a week for a period of 6 months. The training program induced a significant increase in V̊o2max (P < .001) and significant improvements in carbohydrate and lipid metabolism, as reflected by decreased plasma insulin (INS) concentrations measured in the fasting state and after glucose (GLU) ingestion (INS area, P < .001), by reduced plasma cholesterol (C) and low-density lipoprotein cholesterol (LDL-C) levels (P < .001), and by increased ratios of high-density lipoprotein cholesterol (HDL-C) LDL-C and HDL2-C HDL3-C (P < .05 and P < .001, respectively). Changes in body fat mass were positively associated with changes in the INS area/GLU area ratio (r = .49, P < .05) and with changes in very-low-density lipoprotein triglycerides ([VLDL-TG] r = .49, P < .05). Furthermore, changes in the INS area were positively associated with changes in VLDL-TG (r = .51, P < .05). Although no significant mean change in body composition was observed, important individual variation was noted. Twenty women showed a reduction in body fat mass (mean reduction, 2.63 ± 2.2 kg), whereas 11 women showed an increase in adipose mass (mean increase, 2.79 ± 2.36 kg). Comparable increases in V̊o2max were observed between the two groups. The group that showed a decrease in body fat mass with exercise also had significant improvements in carbohydrate and lipid metabolism. Indeed, fasting INS levels (P < .01), INS area/GLU area (P < .01), C (P < .01), and TG (P < .05) levels were all significantly decreased, whereas HDL2-C concentrations (P < .01) and the HDL2-C HDL3-C ratio (P < .001) were significantly increased following training. Women who showed an increase in body fat mass following the 6-month aerobic exercise training program showed a trend for an improved INS sensitivity (P < .06), as estimated by the decrease in fasting INS levels and in the INS area/GLU area ratio. No significant change in lipoprotein-lipid metabolism was noted, although there was a general trend for an improved lipoprotein-lipid profile. Comparisons of absolute and relative changes observed among the two subgroups showed that the improvements in carbohydrate and lipid metabolism in the fat loss group were not significantly different from the changes observed in the fat gainers. These results suggest that aerobic exercise training, per se, irrespective of the changes in total body fat, seems to have beneficial effects on carbohydrate and lipid metabolism that may potentially reduce the risk of coronary artery disease (CAD). However, a concomitant reduction in body fat mass probably amplifies the beneficial effects of aerobic exercise training on metabolism.