You may scoff (Image: Spenser Wilson)

THE holidays are a time of excess. Eat, drink and be merry, for tomorrow we diet. Or perhaps not. Unfortunately, we don’t all have the self-discipline and determination it takes to cut back on cake and hit the gym. But fear not. There could be other ways to shift the fat and stay trim.

Just to get this straight, if you overeat and under-exercise you will gain weight. However, growing evidence suggests that other factors also contribute to excess adiposity. Last year, David Allison at the University of Alabama at Birmingham highlighted this when he discovered that humans are not alone in piling on the pounds. He looked at wild animals, lab animals, even animals kept on the same highly controlled diets for decades, and found that all were becoming heavier (Proceedings of the Royal Society B, vol 278, p 1626). Allison concludes that whatever factors are fattening up the animals that live around us might also help explain the human obesity epidemic.

That being the case, identifying these alternative factors should give us new ways to fight the bulge. The good news is that researchers worldwide are beginning to do just that. It is not yet known how much each factor contributes to obesity, but we can nevertheless suggest ways of avoiding them – and some are far less painful than dieting or pounding the tarmac.


Get vaccinated

If you catch a cold this holiday season you may have to stock up on new clothes as well as tissues. That’s because at least one common cold virus has been linked to obesity. Nikhil Dhurandhar of the Pennington Biomedical Research Center in Louisiana discovered that adenovirus-36 (Ad-36) boosts both the number of fat cells in the body and the amount of fat inside these cells. He also found that obese people are nearly three times as likely as those of healthy weight to test positive for Ad-36 antibodies, indicating current or past infection (Obesity, vol 14, p 1905). Another study reported that children with Ad-36 antibodies weighed an average of 23 kilograms more than children without them (Pediatrics, vol 126, p 721).

The “fat effect” of Ad-36 might persist for several years in humans, although nobody knows for sure. Meanwhile, another 10 microbes have been reported to make animals fatter. While it sounds alarming, this could actually be good news in the fight against flab. “If indeed some infections contribute to obesity in people, we could have a potentially very simple and effective prevention strategy – vaccination,” says Dhurandhar.

Chill!

While extreme stress tends to make people lose weight, the everyday kind can have the opposite effect. So, for the sake of your waistline, take a deep breath, and don’t let the festive family bickering get to you.

Failing that, try giving the new-year diet a miss. One recent study found that moderate calorie restriction made mice much more sensitive to stress, and this effect persisted once the diet was over. The mice went on to choose more high-fat food than those that had never had their food restricted (Journal of Neuroscience, vol 30, p 16399).

Brain imaging studies by Rajita Sinha, director of the Yale Stress Center at Yale University showed that stress increases activity in the ventral striatum, a region associated with reward and habits (Neuropsychopharmacology, vol 36, p 627). “So it increases craving for high-calorie foods in those who have a habit of consuming them,” she says. Instead of counting calories, she recommends mindfulness, stress reduction and meditation techniques to cultivate an awareness of how your thoughts and behaviours can undermine your health. “They can help with taking control over the urges and stress-related eating of high-calorie food.” Everybody say “om”.

Chill some more

Over the past three decades, homes in the US and UK have become warmer. Fiona Johnson at University College London and colleagues think this may be making us fatter (Obesity Reviews, vol 12, p 543). Simona Bo of the University of Turin, Italy, agrees. In a study of more than 1500 middle-aged adults, her team found that those whose home temperatures ranked in the top third were about twice as likely to become obese over the six-year period of the research (International Journal of Obesity, vol 35, p 1442).

Shivering obviously burns energy, but you don’t need to be freezing for your body to chew through extra calories. Most fat on our bodies is a type called white fat. But when temperatures get down to about 18 °C, brown fat – which is abundant in babies and which adults mostly carry around their necks – starts burning energy to warm you up. Unfortunately, if you are not regularly exposed to cold, your brown fat deposits shrink and so too does your capacity to burn off that extra holiday treat. Any change will help, though, says Johnson. You burn steadily less energy as environmental temperatures rise from 15 °C to 28 °C. “So turning down the thermostat by any amount is likely to have some small effect,” she says. Do try this at home.

Eat protein

High-protein diets may be one food fad with substance. First there was Atkins. Now it’s the Dukan diet, reputedly popular with famous figures like the Duchess of Cambridge and supermodel Gisele Bündchen. “There has been no scientific work on its long-term success but based on its composition, we predict it will be effective,” says Alison Gosby at the University of Sydney, Australia.

In October, her team reported that people consumed 12 per cent more calories over four days on a 10 per cent protein diet than they did when given a 15 per cent protein diet (PloS One, vol 6, p 25929). Gosby thinks that is because we have a strong appetite for protein and unconsciously strive to reach our body’s target, so consuming more calories when we are protein-deprived.

Other research indicates that protein keeps you fuller for longer. Better yet, researchers at the University of Copenhagen in Denmark showed that a diet high in protein, and with a low glycaemic index – a measure of its effect on blood glucose levels – allowed most people to eat until they were full without gaining weight (New England Journal of Medicine, vol 363, p 2102). More turkey anyone?

Watch the packaging

As well as looking at the nutritional labelling, you might also want to watch the actual material your food comes wrapped in. Some plastic packaging and cans contain endocrine disrupter chemicals that can leach into food and drinks, and evidence is starting to link some of these to expanding waistlines.

Endocrine disrupters change the normal functioning of hormones. Many interfere with the functioning of the thyroid, which produces hormones that regulate metabolic rate. One group, known as phthalates, also seems to activate a receptor in the cell nucleus called PPAR-gamma, involved in storing fat and metabolising glucose. In 2010, a team led by Elizabeth Hatch at Boston University reported that men with a bigger body mass index (BMI) and waist circumference had higher blood concentrations of metabolites of phthalate (International Journal of Andrology, vol 33, p 324). Other research has linked obesity to exposure to bisphenol A, which is another endocrine disrupter.

Debate continues over whether these chemicals are harmful or not, and avoiding them is tricky. But look out for PVC packaging – labelled “Type 3” for recycling purposes – which can contain phthalates or bisphenol A. And be especially wary when buying fatty foods in which endocrine disrupters tend to accumulate, posing a potential double threat.

Turn down the lights

If your idea of a holiday workout is lifting glasses of beer late into the night, then it’s not just the extra calories you need to worry about. Randy Nelson and his team at Ohio State University in Columbus found that mice exposed to light at night weighed 10 per cent more at the end of the eight-week study than mice that had experienced a standard light/dark cycle, even though they ate the same total number of calories and did the same amount of exercise (Proceedings of the National Academy of Sciences, vol 107, p 18664). Several other studies have found that shift work makes people fatter.

Light at night might alter circadian clock genes, changing an individual’s metabolism, Nelson suggests. “It’s difficult to specify an appropriate light cycle for everyone because people have very different schedules,” he adds. But he recommends keeping a consistent pattern throughout the week and, if possible, avoiding blue wavelengths of light at night (New Scientist, 7 May, p 44). Produced by many LED bulbs, these are known to be especially disruptive to the circadian system.

Move to the country

A brisk walk or jog outdoors can only help in the battle against the bulge, unless you are doing it in a busy city. Breathing polluted air can cause extra fat to accumulate around your stomach and also make your cells less sensitive to insulin, increasing your risk of developing type 2 diabetes. “We believe that air pollution plays a very important role in the current obesity epidemic,” says Xiaohua Xu of Ohio State University.

Breathing polluted aircan cause extra fat to accumulate around your stomach

Xu exposed young mice to air heavily polluted with fine particles for 6 hours a day, five days a week, and found that after 10 weeks they had about 50 per cent more abdominal fat than mice that were fed the same diet but inhaled filtered air. The fatter mice also had elevated blood levels of a protein involved in inflammation called tumour necrosis factor-alpha. Xu believes this may help explain the changes to their fat cells, as well as their decreased sensitivity to insulin.

Another study found a strong link between levels of fine particulate air pollution and the prevalence of type 2 diabetes in North Americans (Diabetes Care, vol 33, p 2196). “We were shocked that the association held up as well as it did,” says John Pearson at Harvard University, who led the research. Fine particles can blow around the globe so you can never entirely escape them, even if you can afford to move out of the city. But if you have a choice, it still might be worth picking a rural ramble over an urban jog.

Have a lie-in

If you need an excuse for spending more time in bed during the holidays, this could be it: too little sleep can make you fat. Bo found that the adults who became obese during her six-year study slept an average of about 6.3 hours a night, compared with about 7.2 hours for those who maintained a healthier body weight. The link between sleep and weight held even when her team took into account other important causes of obesity, such as low levels of physical activity. Rachael Taylor at the University of Otago, New Zealand, has found that children aged between 3 and 5 who sleep less than the average 11 hours a night are also more likely to be overweight or obese by the time they are 7 (BMJ, vol 342, p 2712).

Sleep deprivation reduces the secretion of leptin, a hormone that suppresses appetite, and increases levels of ghrelin, a hormone that stimulates appetite. “Or it could be as simple as less sleep means more time to eat,” says Taylor. Either way, an extra hour in bed sure beats going to the gym.

Sleep deprivation increases levels of ghrelin, a hormone that stimulates the appetite