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That Weight Gain after Exercise May Not Be Muscle Says New Study

Tim Boyer's picture
Weight gain after exercise

Have you ever started an exercise program intending to lose weight, but found yourself actually gaining weight instead? Most of us chalk up that weight gain being due to muscle development. However, a new study reveals that that weight gain after beginning an exercise program may not be muscle after all, but fat.


ABC News recently reported that a surprising finding in a new study performed by researchers at Arizona State University in Phoenix - that was published last month in the Journal of Strength and Conditioning Research - showed that many women who begin an exercise program wind up gaining more body weight as fat rather than as muscle.

The study involved 81 sedentary premenopausal women who were measured for their total body fat before, during and after a 12 week period in which the women exercised three times a week or 30 minutes each on a treadmill at 70% of their maximum endurance.

Based on earlier similar studies, the researchers hypothesized that women with a higher baseline of body fat would lose more body fat in response to exercise training in comparison to women with less body fat; and, that early fat loss during the first few weeks of the testing period would predict final fat loss by the end of testing period.

However, what the researchers actually discovered was that:

• Overall, the women in the study did not lose body weight or fat mass.

• There was considerable individual variability between each participant’s results.

• Fifty-five out of the 81 women actually gained weight with some gaining as much as 10 pounds of extra fat during the12 week long exercise study.

While the amount of calories burned by each woman was monitored closely, what happened after each day is not so clear. All participants were directed to not change their eating habits during the study. However, because the majority of the women did gain weight, the researchers posit that it is due to either eating more, moving around less or a combination of both that led to increased weight gain as fat with the increased exercise.

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The good news, however, is that of those who lost weight during the first 4 weeks of exercise, those women continued to lose weight throughout the study period. According to a quote in the New York Times, study co-author Glenn Gaesser, a professor of nutrition and health promotion at Arizona State advises that 4 weeks into an exercise program is a good time to check on your weight loss progress and make changes if needed.

“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, Dr. Gaesser said. If at that point your weight remains stubbornly unchanged or has increased, “look closely at your diet and other activities,” he said.

Furthermore, the researchers also pointed out that while the overall result was an increase in body fat, there was also an increase in fitness among all of the women.

"Fitness matters far more for health than how much you weigh," stated Dr. Gaesser.

So the end result suggests that exercising alone is not enough for most women― eating habits have to be adjusted as well to achieve successful weight loss. And while the fat may not come off as quickly for one person compared to her exercise partner, both are achieving an overall increase in fitness together. And that’s something to feel good about.

Image Source: Courtesy of ABC News


ABC News: “New Study Finds Exercising Could Make You Gain Weight”

Journal of Strength and Conditioning Research 2014 Oct 28. “Predictors of fat mass changes in response to aerobic exercise training in women” Sawyer, B.J. et al.