- Darker days during the winter make some people reach for certain types of snacks.
- But people tend to think they gain more weight during winter months than they actually do.
- Most people gain around one pound between September and March.
As the days get shorter and the nights get colder, do you find yourself wanting more snacks?
Conventional wisdom suggests that winter is a time to watch the waistline, and research has shown that lots of people do gain some weight in the cloudy winter months.
But studies of hundreds of thousands of people haven't found evidence of any dramatic seasonal weight gain - usually people don't put on more than one pound.
The problem is that single pound can be tough to work off, and combine with more weight over decades. Research from The National Institutes of Health suggests American adults ages 18-49 put on an average of 1-2 pounds every year.
Our bodies in the winter
There is some seasonal variation in what we choose to eat. A 2005 study of 593 predominantly overweight adults found that in the fall, people tend to eat more calories, total fat, and saturated fat. In the spring, folks seem to reach for more carbohydrates.
Research on employees at the National Institutes of Health campus in Maryland in 2000 found that seasonal weight changes over the winter months ranged from less than 1 to 2.2 pounds per person. Most research subjects gained about a pound.
However, they reported believing that they'd packed on about four times more weight than they did, regardless of their size, gender, or race. The researchers didn't know exactly why people thought they put on so much more weight than they did (but perhaps holiday parties and treats might influence that perception).
While we may feel fatter in the winter than we actually are, there are a few environmental differences that can lead us to munch more.
Daily darkness can cause seasonal affective disorder (SAD), a wintertime depression that can leave people feeling moody, glum, and low on energy until longer, brighter days return. The National Institutes of Health estimates that in New England and Alaska - places where winters are long and days are short - SAD affects as much as 9% of the population. (In Florida it's just 1%.)
Swiss researchers have found that people suffering from SAD tend to munch on more carbohydrates and sweets in the winter, as the days get darker.
Less powerful sunshine coupled with a whole lot more bundled up skin also means its tougher for people to soak in vitamin D in the winter, and there may be a link between vitamin D deficiency and weight gain too.
People who spend their whole lives in the sun foraging for food also feel the changing seasons in their gut. A recent study of Hadza hunter-gatherers in Tanzania found the microbes in their intestines change as their diet shifts from more meat in the dry season to more berries when it rains.
The evidence against seasonal weight gain
But science suggests the chilly weather should also help keep us trim. Spending more time outside in the winter can increase the amount of brown fat in the body. Unlike white fat, stored energy that pretty much just sits around like a spare tire, brown fat takes a more active role in the body, burning energy and generating heat. It keeps us warm while chewing through calories at the same time.
Furthermore, winter isn't the only season we're prone to gain weight. Body weight can actually go up by several pounds in the summer, according to army researcher John Castellani, because as we get sweatier, our kidneys retain more fluid. Of course, people are generally more active in the spring and summer, making it easier to lose any extra pounds they put on. Winter pudge, on the other hand, doesn't slide off as easily.
No matter what time of year it is, the latest research suggests we're wired to pay more attention to high-calorie items. So we're more distracted by the sight of a donut than a salad no matter the season.
Harvard nutrition expert Walter Willett, who wrote the book 'Eat, Drink and be Healthy,' told Business Insider that the
If you're prone to snacking but want to consume less food, evidence suggests a surprising strategy: Foods that are crunchy and noisy to eat (like Willett's carrots and apples) have been found to help people control their urge to eat. Scientists call this the "crunch effect:" when people listen to what they're chewing, they eat less of it, no matter what time of year it is.