Effects of insulin resistance on substrate utilization during exercise in overweight women

Abstract

During exercise, obese individuals oxidize less glycogen and more fat than their lean counterparts, but the shift in substrate use may be mediated by insulin resistance rather than body fat per se. In addition, individuals with Type 2 diabetes are not resistant to contraction-mediated glucose uptake during exercise, but in vivo studies uncomplicated by hyperglycemia are lacking. The purpose of this study was to compare blood glucose uptake and the balance between carbohydrate and fat utilization during exercise in insulin-resistant (IR) and insulin-sensitive (IS) women of equivalent body fatness and maximal oxygen consumption (VO2 max). Twelve overweight sedentary women were divided into two groups with similar body mass index (IR = 28.5 +/- 1.6, IS = 27.5 +/- 1.9), lean mass (IR = 42.4 +/- 1.8 kg, IS = 41.5 +/- 1.9 kg), and VO2 max (IR = 29.7 +/- 3.5 ml.kg(-1).min(-1), IS = 30.7 +/- 3.9 ml.kg(-1).min(-1)) but a markedly different composite insulin sensitivity index (IR = 3.0 +/- 0.7, IS = 7.7 +/- 0.9). Blood glucose kinetics and substrate oxidation were assessed by stable isotope dilution and indirect calorimetry during 50 min of treadmill walking at 45% VO2 max. Total carbohydrate oxidation and estimated muscle glycogen use were significantly lower in the IR group. Blood glucose uptake was the same in the IR and IS groups. These data suggest that insulin resistance, independent of body fat, spares muscle glycogen and shifts substrate oxidation toward less carbohydrate use during exercise. Insulin-resistant individuals with normoglycemia appear to have no defect in blood glucose uptake during exercise.

Influence of Insulin Resistance on the Balance between Carbohydrate and Fat Utilization at Rest and in progressive Intensity Exercise

“…There is a possible explanation if we compare to Braun et al study, where differences in insulin resistance between groups were most striking than in the present study, since the authors included in the sample (using the index of insulin sensitivity) subjects with index <4 (insulin resistant) and >7 (insulin sensitive), eliminating individuals who had intermediate values [4] . In this study were included in the samples subjects with a smaller range of insulin resistance.…”

“…This was an important control factor in this study, since excess of body fat, only by itself, can influence the use of fat and carbohydrates [4].…”

“…There were no significant differences in relation to the total rate of fats and carbohydrates oxidation. Importantly, the last two studies cited that subjects were T2DM patients, therefore hyperglycemic, and the movement of glucose from the blood into the tissues may have been facilitated by the action of the body mass [4].…”

“…Aiming to study possible changes in substrate due to insulin resistance, without the influence of hyperglycemia and differences in body composition, Braun et al studied insulin resistant women overweight and obese, but with normal blood glucose, during 50 minutes of walking on a treadmill at 45% VO2 max [4]. A significant decrease was observed in the total carbohydrate utilization in the group of individuals insulin resistant.…”

“…Different researchers have observed that subjects with insulin resistance show changes in their energy metabolism, as in a study conducted with overweight women where the group of insulinresistant oxidized less carbohydrates than the control group [4]. In another study [5] in obese subjects with DM2, was observed a reduced oxidation of plasma fatty acids, but no differencesin the total fat and carbohydrate oxidation, compared to the control group.…”