Randomized trial on the effects of a 7-d low-glycemic diet and exercise intervention on insulin resistance in older obese humans

Abstract

Background: The optimal combination of diet and exercise that produces the greatest reversal of obesity-related insulin resistance is unknown.

Objectives: We examined the effects of a combined 7-d low-glycemic index (low-GI) diet and exercise training intervention on insulin sensitivity in older obese humans.

Design: Participants [n = 32; mean (+/-SEM) age: 66 +/- 1 y; body mass index (in kg/m(2)): 33.8 +/- 0.7] were randomly assigned to a parallel, double-blind, controlled-feeding trial and underwent supervised aerobic exercise (EX; 60 min/d at 80-85% maximum heart rate) in combination with either a low-GI (LoGI + EX: 41.1 +/- 0.4) or a high-GI (HiGI + EX: 80.9 +/- 0.6) diet. All meals were provided and were isocaloric to individual energy requirements. Insulin sensitivity and hepatic glucose production were assessed with a 40-mU x m(-2) x min(-1) hyperinsulinemic euglycemic clamp combined with a [6,6-(2)H(2)]-glucose infusion.

Results: After the intervention, small decreases were observed in body weight (-1.6 +/- 0.2 kg; P < 0.0001) and fat mass (-1.7 +/- 0.9%; P = 0.004) in both groups. Maximal aerobic capacity ( O(2)max) also improved slightly (0.06 +/- 0.02 L/min; P = 0.004). Resting systolic blood pressure, fasting glucose, insulin, triglycerides, and cholesterol all decreased after the study (all P < 0.05). Larger changes in systolic blood pressure and O(2max) were seen in the LoGI + EX group. Insulin-stimulated glucose disposal (P < 0.001), insulin suppression of hepatic glucose production (P = 0.004), and postabsorptive fat oxidation (P = 0.03) improved equally in both groups after the intervention.

Conclusions: These findings suggest that the metabolic improvements after short-term exercise training in older obese individuals are dependent on increased physical activity and are not influenced by a low-GI diet. However, a low-GI diet has added benefit in alleviating hypertension, thus reducing the risk of diabetic and vascular complications.

Figures

FIGURE 1

Study flowchart in response to study advertisement. A total of 413 men and women underwent screening. After review of our inclusion-exclusion criteria, 33 were eligible to partake in the 1-wk diet and exercise intervention. These individuals were randomly assigned to an exercise training protocol (EX) accompanied with either a low–glycemic index (GI) diet (LoGI+EX; n = 16) or a high-GI diet (HiGI+EX; n = 17). After baseline testing, one male subject withdrew from the intervention because of personal circumstances. No adverse events were associated with our testing procedures or the intervention. Final statistical analyses were performed on 32 participants (LoGI+EX, n = 15; HiGI+EX, n = 17).

FIGURE 2

Mean (±SEM) changes in glucose flux of 32 older, obese, and previously sedentary nondiabetic individuals who underwent a 7-d aerobic exercise training intervention (EX) combined with either a low–glycemic index (GI) diet (LoGI-EX; n = 15) or a high-GI diet (HiGI-EX; n = 17). White bars represent prestudy data; black bars represent poststudy data. A: Postabsorptive hepatic glucose production (HGP) showed a nonsignificant decline after the intervention (P = 0.16). B: The percentage of suppression of HGP by insulin increased after the study (P = 0.004). C: Insulin-stimulated glucose disposal rates (GDR) were significantly elevated after the intervention (P < 0.0001). These changes were not different between study groups, nor was there an effect of sex.