DON’T WE NEED TO EAT MORE TO STAY WARM?
This is a common belief -- but it couldn’t be more wrong, says Ahmed Ahmed, consultant gastrointestinal and bariatric surgeon at Bupa Cromwell Hospital.
‘Those who carry excess weight actually feel colder,’ he says.
‘When you put on fat from excess calories it is white adipose tissue; the only fat that keeps you warm is brown adipose tissue, which babies have and which is due to genetic programming.’
While white fat stores energy, brown fat burns calories for heat. So why do we feel like eating more when it turns cold?
In our ancestors’ time, the winter months were associated with famine. One theory is that we’re genetically programmed to increase fat stores in autumn to help us survive -- known as the ‘thrifty gene hypothesis’.
‘The problem is that we no longer need to store fat because we have an abundance of food available all year round. The famine never comes, so we never use up the stores,’ says Mr Ahmed.
Even if the theory were correct, it’s not an excuse for getting tubby.
‘Hypothetically, our genes may favour fat storage; but you can control what happens by making the right food choices.’
BUT I ALWAYS FEEL HUNGRY...
If we wrap up warm when going out and keep our homes well heated, it is unlikely that winter temperatures will contribute to any significant alteration in appetite.
‘Your body maintains its core temperature very tightly, even during winter,’ says Dr Jeremy Tomlinson, an endocrinologist at the University of Birmingham.
So is hunger all in the mind? Maybe not. Melatonin, the hormone triggered by darkness that makes us feel sleepy, can also have a role in appetite.
‘In spring and summer, levels of melatonin decline, but in autumn and winter levels of melatonin increase,’ says Dr Perry Barrett at Aberdeen University, whose research specialises in seasonal weight gain in mammals. ‘This hormone acts on appetite.’
In most mammals, this increase in melatonin reduces hunger -- a strategy to deal with diminished food resources. But in some species the same system produces opposite effects, so it’s possible this could account for increased hunger and weight in humans. Well, it’s a good excuse anyway.
WHY DO I CRAVE COMFORT FOODS?
What may surprise you is that most of us eat more in spring and summer: it’s just the type of food we want that changes in autumn.
‘In spring and summer we take in more carbohydrates, but we develop a tendency for fattier foods in autumn,’ says Dr Barrett.
And that may be driven simply by a desire to cheer ourselves up.
Professor Craig Jackson, head of psychology at Birmingham City University, says: ‘In winter, we tend to develop a lower level of happiness, called ennui. This is basically low level dissatisfaction, which we get when it’s cold, wet and dark.’
He adds that studies show that when we’re suffering with ennui, we use comfort foods as a pick-me-up twice as much as usual.
‘In winter, we go for energy-dense, calorific foods, which tend to be sweeter or fattier,’ says Dr Barrett.
The problem is that these high-sugar snacks will inevitably lead to a sudden drop in blood sugar levels, leaving you craving more energy. You then get into a rollercoaster of highs and lows -- and store the surplus calories as fat.
I DON’T EAT MORE, YET I GET FATTER
research suggests low levels of vitamin D -- the sunshine vitamin -- can affect our weight in winter.
‘Your body needs sunlight to synthesise vitamin D, but in winter there are fewer daylight hours, people go outside less and when they do they wrap up in gloves and scarves, so their skin has little exposure to light,’ says Dr Stephanie Dillon, senior lecturer in Nutrition at the University of Central Lancashire.
Preliminary studies suggest that people with low levels of vitamin D store more fat, though the precise mechanism is still being identified.
‘It appears that lack of vitamin D reduces fat breakdown and triggers fat storage -- so calories you consume are stored in adipose (fat) cells rather than being used for energy,’ says Dr Dillon.
‘Numerous studies show low levels of vitamin D in the overweight and obese.’
Boost your vitamin D levels by eating more oily fish and getting 20 minutes of exposure to sunlight every day, preferably with your forearms uncovered.
IT’S NOT MY FAULT -- I BLAME THE TV
You’re half-right. During the summer months we flock to parks and beaches and enjoy long walks in the sunshine, but come October the sofa suddenly regains its allure.
‘If we’re not out and about, we’re at home -- and that usually means doing activities we associate with eating, such as sitting on the sofa watching TV,’ says Professor Jackson.
He recommends keeping a food diary and thinking carefully about everything you eat.
‘Ask yourself whether you need it, and if you will have a chance to burn off the calories,’ he says.
Mr Ahmed stresses the importance of maintaining an exercise regimen throughout winter.