A substantial number of people who exercise wind up heavier afterward than they were at the start, with the weight gain due mostly to extra fat, not muscle, according to a new study.
But researchers also found, for the first time, that one simple strategy may improve people's odds of shedding pounds while exercising: Eat a more sensible diet, The New York Times reports.
In most of the studies involving exercise and weight lost, people lost barely a third as many pounds as expected, given how many calories they were burning during workouts. Many studies have also found big variations in how people's waistlines respond to the same exercise program, with some people dropping pounds and others gaining fat.
For the research, published by The Journal of Strength and Conditioning Research, scientists at Arizona State University in Phoenix recruited 81 sedentary, overweight women. None had exercised regularly in the past year. The women were asked to exercise, but not change their eating habits in any way.
After 12 weeks, the women were all significantly more aerobically fit than they had been at the start. But many were fatter. Almost 70 percent of the women had added at least some fat mass during the program, and several had gained as much as 10 pounds, most of which was from fat, not added muscle.
A few of the women, though, had lost that much fat or more, and some remained at the same weight as at the start of the regimen.
The researchers suggested that it is likely that those who gained weight began eating more and moving less when they weren't exercising.
"What that means in practical terms is that someone who wants to lose weight with exercise" should step on the bathroom scale after a month, the researchers said. If at that point your weight remains stubbornly unchanged or has increased, "look closely at your diet and other activities."