Exercise-induced improvements in glucose effectiveness areblunted by a high glycemic diet in adults with prediabetes.

Abstract

Glucose effectiveness (GE) refers to the ability of glucose to influence its own metabolism through insulin-independent mechanisms. Diminished GE is a predictor of progression to type 2 diabetes. Exercise training improves GE, however, little is known about how dietary interventions, such as manipulating the glycemic index of diets, interact with exercise-induced improvements in GE in at-risk populations. We enrolled 33 adults with obesity and pre-diabetes (17 males, 65.7±4.3 years, 34.9±4.2kgm-2) into a 12-week exercise training program (1 hday-1 and 5 dayweek-1 at ~85% of maximum heart rate) while being randomized to concurrently receive either a low (EX-LOG: 40±0.3au) or high (EX-HIG: 80±0.6au) glycemic index diet. A 75-g oral-glucose-tolerance test (OGTT) was performed before and after the intervention and GE was calculated using the Nagasaka equation. Insulin resistance was estimated using a hyperinsulinemic-euglycemic clamp and cardiorespiratory fitness using a VO2max test. Both EX-LOG and EX-HIG groups had similar improvements in weight (8.6 ± 5.1kg, P < 0.001), VO2max (6 ± 3.5mLkg-1min-1, P < 0.001) and clamp-measured peripheral insulin resistance (1.7 ± 0.9mgkg-1min-1, P < 0.001), relative to baseline data. GE in EX-LOG and EX-HIG was similar at baseline (1.9 ± 0.38 vs. 1.85 ± 0.3mgdL-1min-1, respectively; P > 0.05) and increased by ~ 20% post-intervention in the EX-LOG arm (∆GE: 0.07-0.57mgdL-1min-1, P < 0.05). Plasma free fatty acid (FFA) concentrations also decreased only in the EX-LOG arm (∆FFA: 0.13 ± 0.23mmolL-1, P<0.05). Our data suggest that a high glycemic index diet may suppress exercise-induced enhancement of GE, and this may be mediated through plasma FFAs.