Why people gain weight as they get older decoded

London : Scientists have found why many people struggle to keep their weight in check as they get older, even if they don't eat more or exercise less than before.

The study, published in the journal Nature Medicine, found that lipid turnover in the fat tissue -- the rate at which lipid or fat in the fat cells is removed -- decreases during ageing and makes it easier to gain weight.

The researchers at Karolinska Institutet in Sweden studied the fat cells in 54 men and women over an average period of 13 years. In that time, all subjects, regardless of whether they gained or lost weight, showed decreases in lipid turnover in the fat tissue.

Those who didn't compensate for that by eating fewer calories gained weight by an average of 20 per cent, according to the study done in collaboration with researchers at Uppsala University in Sweden and University of Lyon in France.

The researchers also examined lipid turnover in 41 women who underwent bariatric surgery, and how the lipid turnover rate affected their ability to keep the weight off four to seven years after surgery.

The result showed that only those who had a low rate before the surgery managed to increase their lipid turnover and maintain their weight loss. The researchers believe these people may have had more room to increase their lipid turnover than those who already had a high-level pre-surgery.

"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," said Peter Arner, a professor at the Karolinska Institutet.

"This could open up new ways to treat obesity," Arner said. Prior studies have shown that one way to speed up the lipid turnover in the fat tissue is to exercise more.

The new research supports that notion, and further indicates that the long-term results of weight-loss surgery would improve if combined with increased physical activity, researchers said.

"Obesity and obesity-related diseases have become a global problem," said Kirsty Spalding, from the Karolinska Institutet.

"Understanding lipid dynamics and what regulates the size of the fat mass in humans has never been more relevant," Spalding said.