Grabbing meals on the go confuses our digestive systems which may be causing some weight gain. Photo / Thinkstock
Grabbing meals on the go confuses our digestive systems which may be causing some weight gain. Photo / Thinkstock
A recent study found that people living on busy roads could blame their bulging waistlines on the noise of the traffic.
Scientists discovered that once the roar of passing vehicles reaches 45 decibels (the level of people talking) men and women start piling on the kilos. They found that for every five decibels louder the noise gets, the waists of people living nearby expand by 21mm (just under an inch).
The investigators, from Sweden's Karolinska Institute, thought noise pollution might raise the amount of the stress hormone cortisol in the body - high levels are thought to make us gain fat around the tummy. But it's not the only unusual thing to blame for our expanding size.
Here, we look at the other strange factors blamed for making us pile on the kilos:
The claim: Lack of vitamin D can lead to weight gain.
The science: Researchers at Aberdeen University studied 3,100 women in the north-east of Scotland in 2008 and found that clinically obese female bodies contain 10 per cent less vitamin D than those of a healthy weight. Dr Helen Macdonald, who led the survey, says: "Lack of sunlight interferes with the hormone leptin which tells our brain when our stomach is full, so we feel compelled to eat more."
In addition, when we are deprived of sunlight, the pituitary gland in the brain also lacks stimulation and our brain responds by thinking it is in the depths of winter, adopting survival tactics such as staying inside, exercising less and eating whatever is available.
"We think obese people are not getting enough sunshine, or that what vitamin D they do have is going into fat stores and is not accessible," says Dr Macdonald.
She compared women in the sun-starved north with thinner women in Surrey and says that lack of rays explains their weight difference. But there may be another reason: Scotland, land of the deep-fried-in-batter Mars Bar, has a notoriously poor diet, whereas Surrey's relatively wealthy inhabitants can afford healthy food.
Buying food with cards
The claim: Paying for food with credit or debit cards encourages you to splurge on fattening treats such as doughnuts, ice cream and chips.
The science: David Just, a professor of behavioural economics at Cornell University in the US, reports that shoppers who pay with plastic spend about 40 per cent more on unhealthy foods than those who pay with cash.
He says that when you use cash, you usually have to plan the purchase in advance, then go to a cash till to withdraw it. This makes you really think about what you need, estimate how much money you'll require and therefore be wary of spending more than you have.
"The act of counting gets you thinking, not just about money, but about the long-term effects of the food," says Professor Just, in his Journal of Consumer Research study of 2012.
Random mealtimes
The claim: Grabbing meals on the go confuses our digestive systems and makes us more likely to put on weight.
The science: Rather than our brain's internal clock, it's our mealtimes that determine how many thousands of genes in the liver - the body's cleaning system - switch themselves on during the day.
If we eat regularly, those genes get into routine habits and work efficiently, say scientists at the Salk Institute for Biological Studies in the US.
But if we eat randomly, our livers aren't ready to process food. Instead, they dump the calories into our bloodstreams and they get stored in our fat reserves, making us bigger.
The report, in the Proceedings of the National Academy of Sciences journal in 2010, says this may explain why people who work alternate shift patterns of nights and days are far more likely to become obese. Indeed, shift work is associated with weight gains of around 4.5kgs a year.
The study makes common sense, but was performed only on mice. It may be that people who eat random meals also consume hurriedly purchased junk food.
Oversleeping
The claim: Too much sleep can make you obese.
The science: A six-year study of people living in Quebec, Canada, found that those who slept for nine or ten hours every night were 21 per cent more likely to be overweight than people who slept between seven and eight hours.
Over six years, they put on 5kg more than the lighter sleepers. The research, published in 2009 in the journal Sleep Medicine, also found that long sleepers were more than twice as likely to develop illnesses such as type 2 diabetes and coronary heart disease - no matter what their weight.
Dr Jean-Philippe Chaput, the lead researcher, admits there is no clear physical explanation. But sleeping for long periods may be linked to depression and unemployment, which are themselves risk-factors for obesity.
Too much sleep may be making you obese. Photo / Thinkstock
Diet drinks
The claim: Low-calorie soft drinks lead you to gorge on high-calorie food.
The science: In 2014, scientists at the John Hopkins Bloomberg School of Public Health in America studied 11 years' worth of US health records and found that adults who consume diet soft drinks have a higher body mass index, which indicates obesity, than those who consume normal sugary drinks.
They discovered that fans of low-calorie drinks are more likely to snack on high-calorie food, as it appears our bodies may realise they're being conned by sweeteners and want to make up for the sugar-deficit. Artificial sweeteners also seem to stimulate our bodies to store fat - a process called adipogenesis.
Worse, a 2013 report in The Journal of Biological Chemistry, says sweeteners also reduce the body's ability to burn off fat. It is believed the artificial chemicals in them confuse our metabolisms.
Low-fat foods
The claim: Full-fat dairy foods make for a slimmer waistline, whereas going low-fat actually makes us plumper.
The science: A fatty acid found in dairy products, called trans-palmitoleic acid, appears to lower people's body weight.
A study of 230 healthy French-Canadians tested their blood for this acid and found the higher its levels, the lower the person's body weight. Trans-palmitoleic acid reduces the level of sugars and fats in the blood, so we have less energy in our bloodstream likely to be converted into fat, according to Canadian researchers in the journal Applied Physiology, Nutrition, and Metabolism in 2010.
People who eat reduced-fat dairy products miss out on this benefit because the fatty acid is removed from things such as skimmed milk and low-fat cheese, and they do not lose weight in similar fashion, says the study.
Being an extrovert
The claim: A wide social circle can increase your girth.
The science: Several international studies have shown that the more people you know, the greater your chance of obesity.
Japanese research among 30,000 people found that extrovert men and women were up to 1.73 times more likely to be obese than their introvert counterparts. The reason, it is claimed, is something called 'social contagion', where we catch habits from each other.
Professor James Fowler, a political scientist at the University of California, has found that a woman's girlfriends affect her physical shape. If one of her friends puts on weight, a woman is then 57 per cent more likely to follow suit.
He says: "Your friends influence your ideas of what to eat, how much to exercise and what body size is appropriate."
The claim: Drinking five or more cups of coffee a day can cause a dangerous form of weight gain.
The science: High coffee intake - around five or six cups per day - increases fat retention in cells around the abdomen and in the liver, reports a 2013 study.
Vance Matthews, a scientist at the Western Australian Institute for Medical Research, blames a compound found in coffee called chlorogenic acid, which actually benefits our waistlines in small doses but has the opposite effect if we have too much because it overloads our metabolisms.
The weight gain may be comparatively small - a few pounds over several years - but it is concentrated around our waists. This type of fat is associated with increased risk of heart attacks and diabetes, says Dr Matthews.
High levels of coffee-drinking also appear to make our bodies resistant to insulin - which is a classic danger sign of developing type 2 diabetes.
The study only looked at mice, but it echoes a report in the Journal of Caffeine Research that warns caffeine can raise insulin resistance in adults.
Drinking 5 or more cups of coffee a day can cause dangerous weight gain. Photo / Thinkstock
Eating quickly
The claim: Bolting meals doesn't give your body time to release hormones in the stomach that make you feel full.
The science: Dr Alexander Kokkinos, of Laiko General Hospital in Athens, Greece, asked people to eat 300ml of ice cream, either in five minutes or 30 minutes. He found that the slow eaters had higher concentrations of two hormones - called PYY and GLP-1 - which are released by the stomach after a meal to tell the brain that it is full.
Those who eat quickly aren't warned by these hormones that it is time to stop and consequently eat too much.
Fast eaters also feel hungry again sooner because it takes the brain up to 20 minutes to process the fact it's consuming food. Bolting it strips us of our ability to remember the sensation of eating.
Writing in the Journal of Clinical Endocrinology & Metabolism in 2010, Dr Kokkinos said: "The warning we were given as children that 'wolfing down your food will make you fat', may have a physiological explanation."
