As we age, it becomes increasingly difficult to control our weight despite keeping caloric intake and exercise intensity constant. One important factor that may be responsible for this age-related effect may be lipid turnover, which decreases in older people, a new study found.

The study performed by a team at the Karolinska Institutet in Sweden studied the fat cells of 54 men and women over a period of 13 years. During this time, all participants showed decreases in lipid turnover in the fat tissue — the rate at which lipids (i.e. fat) is removed and stored.

Adipose tissue mass (body fat) is determined by the storage and removal of triglycerides in adipocytes, also known as fat cells. The new study found that the participants who didn’t compensate for their lower lipid turnover rate by eating fewer calories or exercising more gained 20% more weight on average.

There is still very little we know about how triglyceride storage and removal in adipocytes works, but what has become increasingly clear is that this balance is critical to body fat mass. Previously, studies suggested that one way to speed up lipid turnover in fat tissue is to exercise more, and the new research seems to support this notion.

“Obesity and obesity-related diseases have become a global problem,” says Kirsty Spalding, senior researcher in the Department of Cell and Molecular Biology at Karolinska Institutet and another of the study’s main authors. “Understanding lipid dynamics and what regulates the size of the fat mass in humans has never been more relevant.”

A 2011 study found that triglyceride removal rate from fat tissue is decreased and the amount of triglycerides stored each year is increased in individuals suffering from obesity. In other words, it becomes increasingly easy to gain weight once you pass a certain threshold. Weight gain begets more weight gain, in a vicious cycle that becomes increasingly difficult to break.

The Swedish researchers also looked at lipid turnover in 41 obese women who underwent bariatric surgery. The women’s weight gain was analyzed over a period of four to seven years post-surgery. The results suggest that those who had a lower lipid turnover rate before surgery managed to actually increase their lipid turnover and maintain their weight loss.

“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, a professor at the Department of Medicine in Huddinge at Karolinska Institutet and one of the study’s main authors. “This could open up new ways to treat obesity.”

The findings appeared in Nature Medicine.