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"Weight loss, through calorie restriction or increases in energy expenditure
via exercise, improves glucose tolerance and insulin action," write Edward
P. Weiss, MD, and colleagues from the Washington University School of Medicine
Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE)
Group. "However, exercise-induced energy expenditure may further improve
glucoregulation through mechanisms independent of weight loss.... The purpose
of the present study was to test the hypothesis that exercise training–induced
weight loss results in greater improvements in glucose tolerance and insulin
action than does similar weight loss induced by calorie restriction."
Sedentary men and women aged 50 to 60 years with a body mass index (BMI) of
23.5 to 29.9 kg/m2 were randomized to 12 months of exercise training (n = 18),
calorie restriction (n = 18), or to a healthy lifestyle control group (n = 10).
An oral-glucose tolerance test determined the insulin sensitivity index and
areas under the curve for glucose and insulin. Adiponectin and tumor necrosis
factor alpha (TNF-a) concentrations were measured in fasting serum, and dual-energy
x-ray absorptiometry was used to measure fat mass.
The exercise training and calorie restriction groups had similar yearlong
energy deficits, as reflected in body weight and fat mass changes. The insulin
sensitivity index increased, and the glucose and insulin areas under the curve
decreased in the exercise training and calorie restriction groups and were unchanged
in the healthy lifestyle group and not significantly different between the exercise
training and calorie restriction groups. There were marginally significant increases
in adiponectin and decreases in the ratio of TNF-a to adiponectin in the exercise
training and calorie restriction groups, but not in the healthy lifestyle group.
"Weight loss induced by exercise training or calorie restriction improves
glucose tolerance and insulin action in nonobese, healthy, middle-aged men and
women," the authors write. "However, it does not appear that exercise
training–induced weight loss results in greater improvements than those
that result from calorie restriction alone."
The National Institutes of Health supported this study through some of its
investigators. The authors have disclosed no relevant financial relationships.
Am J Clin Nutr. 2006;84:1033-1042.
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