DON’T BLAME THE CARBS

They’re not the only culprits when it comes to gaining weight – habit and the environment also play a part

Earlier this year, a government report revealed that we are consuming an average of 14 per cent fewer calories than we did in the 1970s. Surely a cause for celebration? Not so fast. While we are eating less, we are also getting fatter. The latest research reveals how our habits and environment are making us bigger, without us even realising it…

CHRONIC STRESS

In February researchers at University College London (UCL) reported that the more stressed people are, the heavier they are likely to be. In stressful situations, cortisol floods the body with glucose, giving muscles the energy to run or fight. Cortisol also inhibits the production of insulin, leaving bloodsugar levels high. With chronic stress, this circulating and unused glucose is stored as body fat or as visceral fat around organs. Thus it’s no surprise that the UCL trial showed that people with higher levels of cortisol were heavier, had a higher body mass index and larger waists, which, according to Dr Sarah Jackson who led the study, is ‘a risk factor for heart disease, diabetes and premature death’.

AIR POLLUTION

Theresa May has said that toxic air is the fourth largest health risk in the UK behind cancer, obesity and heart disease. Studies also suggest that smog-filled air might affect metabolism. Last year US scientists showed that pregnant rats breathing Beijing’s polluted air for three weeks gained significantly more weight than those given clean air to breathe, despite the animals eating the same diet.

SITTING DOWN FOR HOURS

According to recent surveys, most Britons sit or lie down for more than 20 hours a day. ‘Only lying down burns fewer calories per hour than sitting, which uses up less than 70,’ says John Brewer, a professor of applied sport science at St Mary’s University, Twickenham. However, it’s not just the reduced daily calories burnt through a lack of movement that can pile on the pounds. Studies have linked prolonged sitting to a reduction in the enzymes that help to metabolise fat and sugar in the body, exacerbating weight gain.

LATE-NIGHT SNACKING

Last year scientists at King’s College London published two papers in the journal Proceedings of the Nutrition Society showing how the timing of meals influences weight gain. One of the papers found that people who ate their meals with varying frequency – consuming anything from three to nine snacks or meals a day – had less healthy insulin and cholesterol levels and weighed more than those who stuck to a consistent six small meals a day. ‘We found that adults consuming calories during regular meals – at similar times from one day to [the] next – were less obese than people who have irregular meals, despite consuming more calories overall,’ said Dr Gerda Pot, one of the researchers. The other paper included evidence that people who eat more calories later at night are more likely to be obese. At night the body is more likely to store calories consumed as fat than burn them as energy. Studies have also shown that late-night snacking (when your body thinks you should be sleeping) also causes your cells to become more resistant to insulin, causing raised blood-sugar levels and, in time, fat accumulation.

LACK OF SLEEP – OR TOO MUCH

Too much or too little sleep can disrupt your circadian rhythms, causing blood-sugar and metabolic fluctuations, and make extra pounds more likely. Sleeping for fewer than five hours a night is thought to affect the ‘hunger’ hormones – leptin and ghrelin – stimulating appetite so that more high-calorie foods are consumed when you are tired. Too much sleep has been linked to the impaired ability of fat cells to respond to insulin, a fat-storage hormone. According to the University of Glasgow, short sleep duration (less than seven hours) and long sleep duration (more than nine hours) increase the risk of obesity for some people. Dr Jason Gill and his team at the Institute of Cardiovascular and Medical Sciences found that long sleepers with a high genetic risk of obesity were about 4kg heavier, and short sleepers were about 2kg heavier, than those with a similarly high genetic obesity risk who slept regular hours.

ALCOHOL

It’s not just the calories in alcoholic drinks that contribute to weight gain. According to the charity Drinkaware, research shows that alcohol reduces the amount of fat your body burns for energy. Our bodies are able to store protein, carbohydrates and fat, but not alcohol. When our systems need to get rid of alcohol, doing so takes priority and other processes – such as burning fat – are slowed down. The British Dietetic Association’s Aisling Pigott says: ‘When you drink, the liver stops releasing glycogen. That means your blood-sugar levels are lowered and you feel hungrier, leading you to eat more as a result.’

EXCESS SALT

Recent animal trials have suggested a high-salt diet may affect fat cells, making them larger and causing weight gain if you also consume too many calories. In April researchers from the German Aerospace Center, Berlin’s Max Delbrück Center for Molecular Medicine and Tennessee’s Vanderbilt University reported that salty food actually diminishes thirst while increasing hunger. In their trial on ten volunteers, who were put on two simulated flights to Mars, they showed that a high-salt diet caused the kidneys to conserve water so the subjects drank less. The volunteers also complained about being hungry and, in real-life circumstances, that could cause overeating, they said. Researchers observing mice on a high-salt diet found that conserving water in the kidneys required a lot of energy, which could explain why they ate more.

CENTRAL HEATING

Scientists at UCL were among the first to propose that rising central heating use might be linked to obesity. Even turning down the thermostat a couple of notches can make a difference. Cooler temperatures trigger what scientists call a pre-shiver reaction that prompts the body’s stores of good ‘brown’ fat to act. Unlike the white fat that settles on our hips and thighs, brown fat burns calories and prevents weight from piling on by generating about 300 times more heat than any other organ in the body. Three years ago scientists at the Maastricht University Medical Centre reported that setting the thermostat at 19C is sufficient to burn calories – any warmer than that and you could find the pounds creeping on.