It Really Is Genetic
When scientists first discovered it in certain chubby mice, they called it simply the fatso gene. Years later, when they scoured the human genome for markers that increased vulnerability to type 2 diabetes, the fatso gene (now more politely called FTO) showed up there too. Turns out, people with two copies of the gene were 40 percent more likely to have diabetes and 60 percent more likely to be obese than those without it. Those with only one copy of the gene weighed more too.
Scientists now suspect that there are lots of fat genes. “There could be as many as 100 of them,” says Claude Bouchard, PhD, executive director of the Pennington Biomedical Research Center at Louisiana State University System, “each adding a couple of pounds here and a pound or two there. That’s a noticeable difference when it comes to how much more fat we need to burn off.”
Some People Just Have More Fat Cells
And the range is enormous, with some people having twice as many fat cells as others have, says Kirsty Spalding, PhD, of the Karolinska Institute in Stockholm. Even if you’ve lost a few pounds (or gained some), your fat-cell count remains, holding tight to the fat already inside and forever thirsting to be filled up with more. (To add insult to injury, the fat cells of overweight and obese people hold more fat too.)
You Can Change Your Metabolism
Another Scandinavian team looked into what happens at the cellular level when you gain weight. Kirsi Pietiläinen, PhD, an assistant professor of nutrition at Helsinki University Central Hospital, studied sets of twins where one was fat and the other thin, and learned that fat cells in heavier twins underwent metabolic changes that make it more difficult to burn fat. Pietiläinen’s team suspects that gaining as little as 11 pounds can slow metabolism and send you spiraling into a vicious cycle: As you gain more fat, it becomes harder to lose it.