The science behind what makes us put on weight

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.

Learn how to trick your fat genes and keep the weight off.

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.

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.

Don’t miss these simple ways to boost your metabolism.

The most direct route is the food-in-mouth syndrome: stressful circumstances (your bank account, your boss) spark cravings for carbohydrate-rich snack foods, which in turn calm stress hormones. When researchers in one study took away high-carb food from stressed mice, their stress hormones surged.

Stress hormones also ramp up fat storage. For our prehistoric ancestors, stress meant drought or approaching tigers, and a rapid-storage process made sense; we needed the extra energy to survive food shortages or engage in battle. Today we take our stress sitting down – and the unused kilojoules accumulate in our midsection.

To whittle yourself back down to size, in addition to your usual workout routine, make time for stress relief – whether it’s a yoga class or quality time with family.

Don’t ignore these silent signs stress is making you sick.

A mother’s cigarettes increase the risk of low birth weight, and alcohol can damage her baby’s brain. So why wouldn’t unhealthy foods wreak similar havoc? A growing body of science suggests that sugary and fatty foods, consumed even before you’re born, do exactly that. A Pennington study on rodents reports that overweight females have higher levels of glucose and free fatty acids floating around in the womb than in normal-weight females. These molecules trigger the release of proteins that can upset the appetite-control and metabolic systems in the developing brain.

What’s true for mice is often true for humans as well. Doctors from State University of New York Downstate Medical Center compared children born before their mothers had gastric bypass surgery with siblings born later. Women weighed less after the surgery, as expected, but their children were also half as likely to be obese. Because siblings have such similar genetic profiles, the researchers attributed the weight differences to changes in the womb environment. Mums-to-be, take note: you can give your kids a head start by eating well and steering clear of sugary drinks before they’re born.

When patients see Dr Louis Aronne, past president of the Obesity Society, they’re just as likely to have their sleep assessed as their eating habits. If patients are getting less than seven to eight hours, Dr Aronne may prescribe more shut-eye rather than the latest diet or drug. With more sleep, he says, “they have a greater sense of fullness, and they’ll spontaneously lose weight.”

Why? University of Chicago researchers reported that sleep deprivation upsets our hormone balance, triggering both a decrease in leptin (which helps you feel full) and an increase of ghrelin (which triggers hunger). As a result, we think we’re hungry even though we aren’t – and so we eat. Indeed, sleep may be the cheapest and easiest obesity treatment there is.

Find out how to lose weight by planning a weekend sleep in.

When Jodi Dixon’s 188-centimetre, 163 kilogram husband lost 57 kilos, she had mixed feelings. She was the one who always watched her weight and exercised; she was always the one trying to get her husband to be more active. Mort, a medical sales rep, was always the life of the party, says his wife, a 43-year-old mother of two. But when he lost the weight, it was different.

“Men and women would flock to him, drawn to his charisma,” she recalls. “I felt jealous.” Dixon comforted herself with food and gained 10 kilos before she decided to take action. She began bike riding with her husband and enrolled in a diet program. Eventually she trimmed down, too, shedding 15 kilos, and has her sights on losing more.

Dixon credits the weight gain, and the loss, to her jealousy. But research shows that weight gain and loss can be, well, contagious. A study in the New England Journal of Medicine suggests that if one spouse is obese, the other is 37 per cent more likely to become obese, too. The researchers concluded that obesity seems to spread through social networks.

As in Dixon’s case, slimming down seems to be catching, at least within the family: when Dixon launched her weight-loss plan, her eldest daughter, also overweight, followed her mum’s healthy habits and lost 18 kilos.

Adenoviruses are responsible for a host of illnesses, from upper respiratory tract problems to gastrointestinal troubles. The link to fat was uncovered when researchers at the University of Wisconsin injected chickens with the viruses and found that certain strains fattened them up.

Stem cells, known for their chameleon-like abilities to transform, also turned into fat cells when infected with the viruses. “The virus seems to increase the number of fat cells in the body as well as the fat content of these cells,” says associate professor Dr Nikhil Dhurandhar.

Human studies, including comparisons of twins, suggest that obese people are indeed more likely to harbour antibodies for a particular virus, known as adenovirus-36.

We have flu shots; could an obesity vaccine be the next step? It may sound far-fetched, but “that’s what they said about cervical cancer ,too,” says Dhurandhar.

While food is not addictive the way cocaine or alcohol is, scientists in recent years have found some uncanny similarities. When subjects at Monell Chemical Senses Center in Philadelphia were shown the names of foods they liked, the parts of the brain that got excited were the same parts activated in drug addicts. It may have to do with dopamine, the hormone linked to motivation and pleasure, say researchers at Brookhaven National Laboratory in the US. If obese people have fewer dopamine receptors, they may need more food to get that pleasurable reaction.

Are you always hungry? Here are some reasons for why you can’t stop eating.

For years, the team at Linda Bartoshuk’s taste lab at the University of Florida wondered why people who tasted food less intensely than others seemed more likely to be fat. Researcher Derek Snyder had a theory: could an ear infection, which can damage a taste nerve running through the middle ear, be the missing link? After tabulating 6584 questionnaires, the team discovered that those over 35 who had suffered several ear infections had almost double the chance of being obese.

Responses to additional questions provided clues as to why. Former ear-infection patients were a little more likely to love sweets and fatty foods – perhaps because the damaged nerve causes them to have a higher threshold for sensing sweetness and fattiness. Even a small increase in kilojoules from bad food choices adds up over time.

Childhood ear infections are as hard to avoid as the colds that tend to bring them on, but limiting passive smoke seems to drive down incidents of ear infection. If you’re an overweight adult who suffered a severe ear infection as a child, it may be worth paying attention to the taste and texture of your food. Simply finding healthier substitutes, such as fruit instead of sweets or olive oil instead of butter, may help drive you towards eating better and weighing less.