Obesity is a major health concern in the U.S. It is predicted that more than half of all adults living in the U.S. will be obese by the year 2030. A major problem with weight loss is that most people regain lost weight over the next year. Exercise has been shown to be very effective in managing successful weight loss. However, this is not the case for everyone. Recent findings suggest that the weight loss benefit of exercise may depend on your sex.

A study published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology showed that exercise led to different weight loss results in male and female rats. All of the rats ate a low- or high-fat diet for six weeks and then either exercised or were sedentary for another four weeks. The researchers looked at the rats’ body weight, how much they ate and how much energy they expended. They also measured cholesterol, insulin and appetite-controlling hormone levels.

The male rats gained less weight when they exercised. The females still gained weight whether or not they exercised. The female rats that exercised ate more meals and larger meals, while the males ate less. But this only happened on the days that the animals exercised, demonstrating that the changes were not permanent, but an effect of the daily exercise.

The researchers suggest that these findings may apply to people, too. Previous studies have shown that exercising for four months caused the men who volunteered to lose about 11 pounds, with no net weight change in the women who participated. This may correlate with various hormonal differences between men and women. In the study described above, hunger hormone levels rose in the exercised male rats and dropped in the exercised female rats.

What is the take-home message from these findings? While exercise is important in maintaining weight loss, diet control is of equal importance. Women may especially need to conscientiously control their diet with exercise to be able to keep the weight off.