“Weight gain over the holidays is a large part of the typical weight gain that adults have over the years,” says Dr. Jack Yanovski, head of the Unit on Growth and Obesity at NIH. He and his colleagues found that almost all the weight people had gained over the course of a year could be explained by the pounds they added over the holiday period. That’s why it’s particularly important to make sure you maintain your weight during the holiday season.

Maintaining weight is a matter of balance—energy balance. If you take in more calories than you burn in physical activity, you store the extra energy around your body, mostly as fat, and gain weight. To maintain your weight, you need to balance the energy you take in with the energy you burn.

Karen Donato, coordinator of NIH’s Obesity Education Initiative, points out that you don’t have to balance your calories every day. “It’s the balance over time that determines whether you can maintain a healthy weight in the long run,” she says.

Yanovski explains that our bodies’ energy controls are very accurate. “Over the course of the year,” he says, “the average adult consumes about 912,500 calories.” Someone who eats just an extra 4,050 calories or so a year will gain a pound over the course of that year. That’s only about 11 calories a day. To put this in perspective, break a rice cake into 4 pieces or a pretzel rod into 10. One piece is 11 calories.

“You can see that very small imbalances that would be easy to miss could account for the average weight gain that we see,” Yanovski says.

Genetics and other factors affect how your body uses the calories you consume. Still, the only way to gain weight is by taking in more calories than you burn. If you’re overweight, talk to your doctor about how to lose those extra pounds. Many NIH-funded researchers, including Yanovski’s team, are working to understand the complex causes of obesity and to develop better ways to combat it.

If you keep your weight in check for most of the year but have trouble during the holidays, Yanovski offers some advice that might help.

First, be active. In their study of holiday weight gain, Yanovski and his team noted that people who reported being much more active maintained their weight or even lost weight during the holidays. Those who reported being less active gained the most during this period. If you exercise regularly, keep it up over the holidays. If you’re not active now, get started and make a serious New Year’s resolution to stick with it. Add physical activity to your daily routine, such as taking the stairs instead of the elevator, or walk briskly in the mall. If a holiday party includes dancing, join in!

If you have any control over the scheduling of holiday food celebrations, make them at normal meal times. Holding celebrations outside of normal meal times encourages people to pile on excess calories. If your celebration is at a regular meal time, revelers will be more likely to eat responsibly.

When you’re at a holiday celebration, watch out for soda and other sweetened beverages. A 12-ounce can of soda can have more than 150 calories. A 16-ounce glass of punch or lemonade can have over 200 calories. Don’t overdo natural fruit juices, either, since they also carry many calories. It’s best to go with calorie-free bottled water, plain or sparkling, when it’s available. Diet beverages made with artificial sweeteners can help you control your calories at celebrations, although drinking them on a regular basis may not help with long-term weight control.

Alcohol can be a major source of hidden calories as well. A single shot of liquor, about 2 ounces, is nearly 125 calories. A 5-ounce glass of wine or a 12-ounce glass of beer is about 160. Sweet mixed drinks have even more calories. An 8-ounce margarita, for example, has 240 calories.

Choose foods that are lower in energy density, meaning they have fewer calories for their size. You’ll feel fuller sooner and take in fewer calories. So, for example, start out your meal with a salad or soup. Skip the second helpings of stuffing, mashed potatoes and gravy; go for more vegetables instead. If you’re bringing dessert, serve angel food cake, ginger bread or fruit instead of brownies, pound cake or chocolate cake.

One good strategy is to try to avoid high-fat foods. Fat in itself may not be the key to weight control as people once thought, but it does have high energy density. If you cut back on foods that are high in fat, you’ll likely cut down on the calories. So use low-fat or skim milk instead of whole milk or half-and-half. Skip the butter. Eat your turkey without the skin. And cut away the visible fat from meats.

Other strategies are to eat a healthy snack before a holiday celebration to avoid overeating later, and to use smaller plates when they’re available. Yanovski says, “There’s pretty good evidence to suggest that the bigger the plate and the more food that’s on the plate, the more people will eat at a given meal.”

No matter how much you weigh, it’s wise to watch your weight over the holidays. It’s better to keep it off now than to try to lose it later.