Circulating cytokines as determinants of weight loss-induced improvements in insulin sensitivity

Abstract

Dietary calorie restriction and exercise promote weight loss and may have additive effects for improving insulin sensitivity, independent of weight loss. It is not known if these effects are attributable to changes in circulating cytokines. We evaluated the hypothesis that modest, matched weight loss induced by calorie restriction and exercise have additive effects on circulating cytokines and these changes correlate with improvements in insulin sensitivity. Overweight and sedentary women and men (n = 52, 45-65 years) were randomized to undergo 7 % weight loss by using 3-6 months of calorie restriction, exercise, or a combination of both calorie restriction and exercise. Concentrations of cytokines and hormones were measured in fasting and oral glucose tolerance test blood samples. Insulin sensitivity was estimated based on oral glucose tolerance test for glucose and insulin. With all groups combined, fasting leptin (p < 0.0001) and high molecular weight adiponectin (p = 0.04) decreased and pentraxin-3 increased (p < 0.0001), in a manner that correlated with improvements in insulin sensitivity (all p ≤ 0.0002). These changes, combined with decreases in glucose-dependent insulinotropic polypeptide from the oral glucose tolerance test, explained 63 % of the variance (p < 0.0001) in insulin sensitivity improvements. Exercise and calorie restriction had additive effects on leptin, with a similar trend for high molecular weight adiponectin. Monocyte chemoattractant protein-1 and C-reactive protein concentrations did not change. Calorie restriction and exercise had opposite effects on soluble tumor necrosis factor receptor-1. Modest weight loss in overweight adults decreases serum leptin and high molecular weight adiponectin, and increases pentraxin-3 concentrations in a manner that correlates with increased insulin sensitivity. Exercise has additive effects to those induced by calorie restriction for reductions in leptin and possibly adiponectin. These changes may contribute to the additive effects of calorie restriction and exercise for improving insulin sensitivity.

Keywords: Adipokine; Adiposity; Aerobic exercise; Diet modification; Insulin resistance.

Figure 1

Changes in body composition and measures of glucoregulation. Values are least squares means ± SE that have been adjusted for differences in baseline values among groups. P-values reflect the significance of the among-group differences in change values after adjustment for baseline values using ANCOVA. For each outcome, means with unlike superscripts are significantly different (P<0.05). These data have been presented previously [5] but are included in the present report to assist in interpreting the cytokine data.