Once you reach a certain age, it can seem as if you gain weight simply by breathing. Well, it turns out there is likely a biological reason for that. A new study suggests that the way our bodies process fat changes as we age, but we can combat this tendency with — what else — exercise.

The obesity rate in the U.S. is just under 40 percent, according to the most recent data from the Centers for Disease Control and Prevention. The association between obesity and the risk of death increases with age, and that makes obesity among older adults a great concern.

Processes in our fat tissue regulate changes in body weight during aging in a way that is independent of other factors. This could open up new ways to treat obesity.

Researchers at Karolinska Institutet and Uppsala University in Sweden, as well as the University of Lyon in France, studied the fat cells of over 50 men and women for about 13 years. All of the participants in the study experienced a decrease in lipid turnover in their fat tissues, whether they gained weight or lost weight during that period of time. Lipid turnover refers to the rate at which fat in the fat cells is transported out of the cells and stored elsewhere in the body.

The weight of the people who did not compensate for the decrease in lipid turnover by eating fewer calories increased by an average of 20 percent.

The researchers also looked at the lipid turnover rate of women who had undergone weight-loss surgery. Of the women studied, only those who had a low lipid turnover rate before surgery were able to increase it and maintain their weight loss for four to seven years after surgery. Perhaps these women had more room for improvement in lipid turnover than the women who already had a high level before surgery, theorized the researchers.

“The results indicate for the first time that processes in our fat tissue regulate changes in body weight during ageing in a way that is independent of other factors,” says Peter Arner, one of the study's authors, in a statement. “This could open up new ways to treat obesity.”

Previous research has shown that lipid turnover in fat tissue can be sped up by exercising more, and this study supports that idea. It also suggests that the long-term results of weight-loss surgery can be improved if patients increase their physical activity.

The message for everyone is to make being physically active a part of your life. Even without changing the amount you eat as you age, weight gain is likely, and the best way to prevent that is to get out and get moving.

The study was published in Nature Medicine.