It has been quite notable that older people gain weight easily. Previous research has suggested that excess fat consumption makes it difficult for the body to metabolise fats. New research now published in Nature Medicine has expanded this theory. Results from this study indicate that the body’s ability to turnover or metabolise fats decreases with increasing age making it easier to gain weight (1). Therefore there is a net shift in balance towards accumulation of fat regardless of exercise and diet.
Scientists came to the conclusion that ageing causes decline in fat turnover by performing a clever experiment. They assessed fat content in body cells of subjects over the span of a decade. They did so by measuring the levels of an isotope of carbon called 14C in fat tissue. This isotope of carbon was used during the cold war for nuclear bomb testing. Since then, it has been found in the atmosphere of earth. Its incorporation into the body has been consistent across all people. Therefore, its measurement in the body gave the scientists an indirect measurement of fat turnover. For example, less amount of this isotope present at later stages of life would mean high fat metabolism indicating less weight gain.
The scientists studied fat cells in 54 men and women over an average period of 13 years. All subjects, regardless of whether they gained or lost weight, showed decreases in lipid turnover in the fat tissue. Turnover means 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.
The scientists also examined lipid turnover in 41 women who underwent bariatric surgery (obesity surgery). They measured how 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 scientists 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,” says Peter Arner, 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.”
Prior studies have shown that one way to speed up the lipid turnover in the fat tissue is to exercise more. This new research supports that notion and further indicates that the long-term result of weight-loss surgery would improve if combined with increased physical activity.
“Obesity and obesity-related diseases have become a global problem,” says Kirsty Spalding, senior researcher at 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.”
- 1.P. Arner, S. Bernard, L. Appelsved, K.-Y. Fu, D. P. Andersson, M. Salehpour, A. Thorell, M. Rydén, K. L. Spalding, Adipose lipid turnover and long-term changes in body weight. Nat Med, 1385–1389 (2019).