Many people struggle to keep their weight in check as they get older. Now new research at Karolinska Institutet in Sweden has uncovered why that is: Lipid turnover in the fat tissue decreases during ageing and makes it easier to gain weight, even if we don't eat more or exercise less than before. The study is published in the journal Nature Medicine. The scientists 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, that is the rate at which lipid (or fat) in the fat cells is removed and stored. Those who didn't compensate for that by eating less calories gained weight by an average of 20 percent, according to the study which was done in collaboration with researchers at Uppsala University in Sweden and University of Lyon in France.