It really is genetic
When scientists first discovered the gene in certain chubby mice, they called it 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 per cent more likely to have diabetes and 60 per cent 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,” says Dr Claude Bouchard, executive director of the Pennington Biomedical Research Center. “Each add 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.”
As much as 16 per cent of the population has two copies of the FTO gene, and half of us have one copy. So far, scientists suspect that the other possible obesity-promoting genes have a small effect compared with FTO. The good news? “A genetic predisposition isn’t necessarily a life sentence,” says Bouchard. Also, even though FTO gene carriers are more likely to be obese, the gene doesn’t prevent you from losing weight, according to a 2016 study from Newcastle University. “Our study shows that improving your diet and being more physically active will help you lose weight, regardless of your genetic makeup,” said lead researcher John Mathers.
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 Dr Kirsty Spalding, of the Karolinska Institute in Stockholm. Even if you’ve lost a few kilograms (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.
New fat cells emerge during childhood but seem to stop by adolescence. Those of us destined to have a lot of these cells probably start producing them as young as age two. The cells’ rate of growth may also be faster – even if kids cut right back on kilojoules.
Strangers have written to Spalding, telling her how depressed they are by her research. But she says her news isn’t all bleak. You’re better off with more fat cells, she says, than with fewer fat cells that become overstuffed and enlarged. New research suggests that the overstuffed group are more vulnerable to obesity – related health complications. So while you can’t reduce your total number of fat cells, there are things you can do to keep them small.
You can change your metabolism
Another Scandinavian team looked into what happens at the cellular level when you gain weight. Assistant professor of nutrition, Dr Kirsi Pietiläinen, 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 five kilograms can slow metabolism and send you spiralling into a vicious cycle: as you gain more fat, it becomes harder to lose it.
How to get back on track? “The more I learn on the job, the more I’m convinced we need physical activity,” Pietiläinen says. Once a chubby child herself, she now runs regularly and is at a healthy weight.