Yale Bulletin and Calendar

January 17, 2003|Volume 31, Number 15|Two-Week Issue

Study shows benefits of exercise
in reducing intra-abdominal fat

Regular exercise, such as brisk walking, reduces total and intra-abdominal body fat among overweight and obese postmenopausal women, a study by a Yale researcher has found.

This exercise-induced weight loss also had greater health benefits than weight loss through diets, says the study's lead author, Melinda Irwin, assistant professor in the Department of Epidemiology and Public Health at the School of Medicine.

"Previously sedentary postmenopausal women who exercised for more than 195 minutes per week lost 6.9% of intra-abdominal body fat and maintained their energy intake during the 12-month study, compared with less significant losses and even gains among women in the control group," says Irwin.

Published in the Jan. 15 issue of the Journal of the American Medical Association, the study looked at 173 physically inactive postmenopausal women between the ages of 50 and 75 living in Seattle, Washington, from 1997 to 2001. Participants were randomized to a group that did exercise of moderate intensity five days a week or a group that only stretched one day a week. The researchers measured changes in body weight, total body fat, intra-abdominal fat and subcutaneous-abdominal body fat at the start of the study and after one year.

"While weight loss was modest (a loss of 1.3 kg or 1.6% over 12 months), intra-abdominal body fat loss, measured by computed tomography -- a gold standard of assessing abdominal body fat -- was considerable at 5.8% and dose-dependent," Irwin said. "Women randomized to the exercise group who increased their fitness level by more than 16% lost 10.8% of intra-abdominal body fat."

Irwin notes that unlike diet-induced weight loss, exercise-induced weight loss increases fitness levels. "In our study, 84% of the exercisers improved their cardiorespiratory fitness level," she said. "High levels of fitness reduce the rate of cardiovascular morbidity and mortality, independent of obesity."

Irwin said that the increasing prevalence of obesity is a major public concern. Over half of the U.S. adult population is overweight. Obesity increases the risk of several chronic diseases, and intra-abdominal body fat -- independent of total body fat -- is associated with insulin resistance, type 2 diabetes, hypertension, cardiovascular disease and some cancers.

Exercise may counteract the aberrant metabolic profile associated with intra-abdominal body fat, says Irwin, who conducted the study with principal investigator Dr. Anne McTiernan at the Fred Hutchinson Cancer Research Center in Seattle. The study was funded by the National Cancer Institute.

"Numerous adaptive responses take place with exercise training including development of a more efficient system for transfer of oxygen to muscle," says Irwin. "With this more efficient system, muscles can increase their use of lipid stores rather than relying on carbohydrate reserves. Exercise helps to counteract the weight regain often observed after diet-induced weight loss."

Individuals should not be discouraged if they observe only modest changes in body weight, Irwin adds.

"Keep exercising," she advises. "A regular exercise program pays off in more ways than one. Our findings support the important role of exercise in reducing body fat, especially intra-abdominal body fat. Overweight women should participate in moderate-intensity exercise, such as brisk walking, as a method for obesity reduction and chronic disease prevention."

Other authors on the study included Yutaki Yasui, Cornelia M. Ulrich, Deborah Bowen, Dr. Rebecca Rudolph, Dr. Robert S. Schwarz, Dr. Michi Yukawa, Erin Aiello and Dr. John D. Potter.

-- By Karen Peart

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