Randomized trial on the effects of a 7-d low-glycemic diet and exercise intervention on insulin resistance in older obese humans.
BACKGROUND
The optimal combination of diet and exercise that produces the greatest reversal of obesity-related insulin resistance is unknown.


OBJECTIVE
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.


METHODS
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.
Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH44195, USA.
Thomas P J
TP
Solomon
Jacob M
JM
Haus
Karen R
KR
Kelly
Marc D
MD
Cook
Michelle
M
Riccardi
Michael
M
Rocco
Sangeeta R
SR
Kashyap
Hope
H
Barkoukis
John P
JP
Kirwan
D000368:Aged; D001794:Blood Pressure; D001823:Body Composition; D015992:Body Mass Index; D001835:Body Weight; D002149:Energy Intake; D015444:Exercise; D005260:Female; D038321:Glycemic Index; D006339:Heart Rate; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D008074:Lipoproteins / Q000097:blood; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D010101:Oxygen Consumption; D010809:Physical Fitness
D008074:Lipoproteins