(07-10-09) Randomized trial on the effects of a 7-d low glycemic diet and exercise intervention on insulin resistance in older obese humans.

Solomon TP, Haus JM, Kelly KR, Cook MD, Riccardi M, Rocco M, Kashyap SR, Barkoukis H, Kirwan JP.
Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH and the Department of Nutrition, Cleveland Clinic, Cleveland, OH.

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 . m(-2) . min(-1) hyperinsulinemic euglycemic clamp combined with a [6,6-(2)H(2)]-glucose infusion.
RESULTS: After the intervention, smalldecreases 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) were equally improved 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.


Source: Am J Clin Nutr. 2009 Sep 30.

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