Physiological measurement of insulin action across a range of insulin sensitivities

S328-S32

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

Energy surplus raises circulating concentrations of leptin and insulin while lowering plasma ghrelin. Exercise has the opposite effects. The purpose of this study was to determine whether exercise counters the hormonal effects of energy surplus independent of changes in energy balance. To do that, we assessed plasma concentrations of leptin, insulin, and ghrelin at baseline, after overfeeding, and after overfeeding plus exercise. Baseline (B) leptin and insulin concentrations and ghrelin area under the curve were measured during an oral glucose challenge in 9 healthy, active subjects (6 male, 3 female) after 2 days in energy balance without exercise. Measurements were repeated after subjects were overfed by +3213 ± 849 kJ/d for 3 more sedentary days (OF). In the third condition, the same net energy surplus (+3125 ± 933 kJ/d) was generated for 24 hours by doubling the overfeeding (+6284 ± 1669 kJ/d) and countering it with a bout of exercise (expenditure = 3063 ± 803 kJ); and measurements were made the next day (OF + EX). Compared with B, leptin went up (5.8 ± 8.2 to 7.6 ± 10.6 ng/mL) after OF, but was not significantly higher after OF + EX (7.1 ± 10.2 ng/mL). Compared with B, insulin was +36% and +43% higher after OF and OF + EX, respectively. In contrast, ghrelin area under the curve did not change after OF but was significantly lower (−14%) than B or OF after OF + EX (indicating greater suppression). These data suggest that the effect of short-term exercise on fasting leptin and insulin depends on energy balance but the ghrelin response may be partially mediated by effects of exercise independent of energy balance

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

393-39

The effect of carbohydrate availability following exercise on whole-body insulin action

One bout of exercise enhances insulin-stimulated glucose uptake (insulin action), but the effect is blunted by consumption of carbohydrate-containing food after exercise. The independent roles of energy and carbohydrate in mediating post-exercise insulin action have not been systematically evaluated in humans. The purpose of this study was to determine if varying carbohydrate availability, with energy intake held constant, mediates post-exercise insulin action. Ten young (21 +/- 2 y, overweight (body fat 37% +/- 3%) men and women completed 3 conditions in random order: (i) no-exercise (BASE), (ii) exercise with energy balance but carbohydrate deficit (C-DEF), and (iii) exercise with energy and carbohydrate balance (C-BAL). In the exercise conditions, subjects expended 30% of total daily energy expenditure on a cycle ergometer at 70% VO2 peak. Following exercise, subjects consumed a meal that replaced expended energy (~3000 kJ) and was either balanced (intake = expenditure) or deficient (-100 g) in carbohydrate. Twelve hours later, insulin action was measured by continuous infusion of glucose with stable isotope tracer (CIG-SIT). Changes in insulin action were evaluated using a one-way ANOVA with repeated measures. During CIG-SIT, non-oxidative glucose disposal (i.e., glucose storage) was higher in C-DEF than in BASE (27.2 +/- 3.2 vs. 16.9 +/- 3.5 micromol.L-1.kg-1.min-1, p \u3c 0.05). Conversely, glucose oxidation was lower in C-DEF (8.6 +/- 1.3 micromol.L-1.kg-1.min-1) compared with C-BAL (12.2 +/- 1.2 micromol.L-1.kg-1.min-1), and BASE (17.1 +/- 2.2 micromol.L-1.kg-1.min-1), p \u3c 0.05). Fasting fat oxidation was higher in C-DEF than in BASE (109.8 +/- 10.5 vs. 80.7 +/- 9.6 mg.min-1, p \u3c 0.05). In C-DEF, enhanced insulin action was correlated with the magnitude of the carbohydrate deficit (r = 0.82, p \u3c 0.01). Following exercise, re-feeding expended energy, but not carbohydrate, increased fasting fat oxidation, and shifted insulin-mediated glucose disposal toward increased storage and away from oxidation

Effect of timing of energy and carbohydrate replacement on post-exercise insulin action

1139-114

Metformin’s Effect on Exercise and Postexercise Substrate Oxidation

63-7

Effect of timing of energy and carbohydrate replacement on post-exercise insulin action

The nutritional environment surrounding an exercise bout modulates post-exercise insulin action. The purpose of this study was to determine how timing energy and carbohydrate replacement proximate to an exercise bout influences exercise-enhanced insulin action. To create an appropriate baseline, sensitivity to insulin was reduced in 9 healthy young men (n=6) and women (n=3) by 2 days of energy surplus and detraining. Then, insulin action (glucose uptake per unit plasma insulin) was assessed by stable isotope dilution during a continuous glucose infusion 12 h after a standardized meal under 4 conditions. In 3 conditions, the meal replaced the energy and carbohydrate expended during an exercise bout (62.9+/-2.8 min cycle ergometry at 65% VO2 peak followed by ten 30 s sprints). The meal was given before (Pre), immediately after (ImmPost), or 3 h after exercise (Delay). The 4th condition was a no-exercise control (Control). Data were analyzed using linear mixed-effects models with planned contrasts. Relative to Control, insulin action increased by 22% in Pre (p=0.05), 44% in ImmPost (p\u3c0.01), and 19% in Delay (p=0.09). Non-oxidative disposal was higher, and oxidative disposal was lower in ImmPost relative to Control and Pre (p\u3c0.05). Hepatic glucose production was suppressed by the infusion to a greater extent in Pre and Delay (76.9%+/-8.8% and 81.2%+/-4.7%) compared with ImmPost (64.7%+/-10.0%). A bout of exercise enhances insulin action even when expended energy and carbohydrate are replaced. Further, timing of energy and carbohydrate consumption subtly modulates the effectiveness of exercise to enhance insulin action