Health experts often argue that moderate exercise can cut the risk of disease even if it doesn't help with weight loss.
A new study published in The Journal of the American Medical Association shows how.
While a group of women who worked out for a year lost an average of only three pounds more than a group that didn't, the ones who exercised made sharp reductions in the fat in their midsections, where it appears to be most dangerous.
What the researchers call intra-abdominal fat is harder to see than the padding immediately under the skin, but having an abundance of of fat surrounding the organs has been linked to a greater incidence of diabetes, heart disease and cancer.
In the new study, researchers measured the fat levels of 168 sedentary and overweight postmenopausal women.
Half of the women were required to exercise moderately for 45 minutes a day, five days a week.
For the first three months, they worked out in supervised sessions at a gym three days a week.
For the next nine months, they went to the gym at least once a week but did the bulk of their workouts at home.
The other half attended stretching classes once a week.
Twelve months later, the women who worked out — for an average of 37 minutes five times a week — had made the biggest change in their bodies' composition, losing about 7 percent of their intra-abdominal fat.
Women who worked out but not quite as much had significant but smaller reductions. Those who only stretched were essentially unchanged, both in weight and body composition.