These cold, dark winter days make me want to curl up with a book, perhaps while munching on holiday cookies.One could describe my conduct this way: sedentary behavior combined with snacking on sugary treats. A regular practice of these things may well lead to weight gain.Is winter weight gain a thing? Yes, says Larry Cheskin, who chairs the nutrition department at George Mason University. “There is good evidence that it is a thing.”On average, research shows that people gain one to two pounds over the winter months. For instance, a study of 195 people at the National Institutes of Health found weight gain of about one pound between late September and March.A study of 248 U.S. military personnel, who were enrolled in a weight-loss program, found that people added about two pounds from fall to winter.Here’s something else. There also is evidence that American adults gain one to two pounds each year, gradually accumulating weight over decades. Winter weight gain may be a major culprit, so perhaps we should view the season as a particularly risky time for adding excess padding.Indeed, 165 subjects in the NIH study returned for a September weigh-in and, on average, were 1.4 pounds heavier than the year before.A note: One to two pounds on average means that some people don’t gain any weight while others gain five pounds or more. And in a rude twist of fate, the people who gain the most are more likely to be already overweight or obese.Why does winter weight gain happen? “The reasons are not that clear,” Cheskin says. “I suspect that much of it is what we would call behavioral.”That means eating more and exercising less.“The change in eating behavior is key,” says Michael Gavin, a physician at the University of Rochester Medical Center. Overeating, snacking and choosing comfort foods over fruits and vegetables are some of the eating habits that may occur.Some researchers have narrowed the time window to look at weight gain over the weeks spanning Thanksgiving through New Year’s. In the NIH study, people gained 0.8 pounds, on average, during that period. And in a second study with military personnel, it was 0.4 pounds.People celebrate a variety of things over the holidays — seeing family, religious events, the turning of the calendar — and they do it with rich foods, desserts and drinks. Perhaps we should mention the holiday spirit — a spirit of permission to overindulge. I mean, we’re celebrating!“The holidays are not insignificant,” Cheskin says. There are more social events, an increase in the variety of foods and more drinking. Alcohol adds calories and undermines self-control.But it’s not just overeating at holiday parties that’s to blame. When it’s cold and snowy — or slushy or icy — outside, people spend more time indoors, which in turn can mean getting less physical activity.Research backs up the exercise slowdown. A review of 37 studies found that people are most physically active in spring and summer and least in winter.Also, it’s easy to feel bored when you’re cooped up inside — and boredom may lead you to snack more.So if wintertime in general, and the holidays in particular, are a precarious time for gaining weight — weight that you might keep forever — then what can be done?First, be aware that winter weight gain can happen. Pay attention to your diet and try to keep your activity level up.Weighing yourself every day is key, says Margeret Fahey, a doctoral student at the University of Memphis and first author on the military personnel’s weight-gain studies. Study participants used electronic scales that sent data directly to the researchers. Fahey and her colleagues observed that during the winter months, people often skipped their daily weigh-ins.The researchers also noticed that the participants who had most recently enrolled in the weight-loss intervention gained the least weight. That suggests that when motivation is high, winter weight gain can be avoided.Motivation can help you stick to good weight maintebioreportsce behaviors, such as daily weigh-ins, as well as tracking diet and activity. There are a number of apps that can make it easier to track what you eat and how much you move.“Winter weight gain is common,” Fahey says. “Which might indicate that weight maintebioreportsce strategies are important to implement during winter.”Gavin recommends being mindful of your eating habits, but not overly restrictive. Don’t try to avoid cookies altogether, he says, but limit yourself to one or two cookies.Cheskin says it’s important to understand your own tendencies. When counseling patients who want to lose weight, he starts by asking them what they think has contributed to their weight gain. Do you eat when you’re sad or bored? Do you plan your meals? Do social outings — or family — interfere with healthy eating? Are there medical issues involved?“You hear about lots of factors relating to weight,” Cheskin says. You don’t need to attend to all of them, he says — just the ones that are specific to you.