The research also found that it can take five months to get back to your normal weight.

Your boot-camp class won't change the number on the scale if you're committing these errors outside of your sweat sessions: You think about burn only in the gym: "You get strong in the gym—but you get lean in life," says celebrity trainer Harley Pasternak, who encourages his clients to wear pedometers and log more than 10,000 steps per day. You aren't food-focused: A recent study in Current Biology suggests there's a limit to how many calories we burn through physical activity; after torching more than a moderate amount, our bodies make it hard to let precious energy go. The fix is in the kitchen: "To drop 1 to 2 pounds a week, cut about 2,000 calories weekly through diet and exercise," says Jordan.You're not as active as you think: One study out of York University in Toronto found that even when people were told what "vigorous" exertion should feel like, they still underestimated how much effort a physical activity actually required. A heart-rate monitor can help give you a more realistic idea of your effort and burn. 
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Holiday weight gain is real, says new research from Cornell University, and it’s not just Americans who are affected. What’s more, the study showed that the extra pounds you put on between Halloween and Christmas can take more than five months to lose.

The new research, led by Cornell’s Food and Brand Lab as well as scientists in Finland and France, looked at year-round weight patterns of nearly 3,000 people in the United States, Germany, and Japan. Their data came from daily weigh-ins of consumers who’d purchased wireless Withings scales and had agreed to have their measurements collected and analyzed.

In the United States, the researchers found that the participants’ weight began to rise throughout October and November, and peaked 10 days after Christmas. The change wasn’t large, but it was significant: On average, people’s weight increased about 1.3 pounds during the Christmas-New Year’s season.

About half of that weight came off quickly after the holiday season ended, but the other half wasn’t lost until about five months later, after Easter.

Similar trends were noted in the other countries, as well. People in Germany tended to weight the most around New Year’s and Easter, and those in Japan packed on pounds around New Year’s as well as Golden Week—the country’s other major holiday—in April.

The findings were published last week as a research letter in the New England Journal of Medicine. “Different countries celebrate different holidays, but many such celebration periods have one thing in common: an increased intake of favorite foods,” the authors wrote.

Although the topic of holiday weight gain comes up every year, some research has found that the phenomenon is more a myth than a reality—or at least that it’s greatly exaggerated in the media and pop culture. In a 2013 study from Texas Tech, for example, participants gained only about a pound and a half between Thanksgiving and New Year’s.

Brian Wansink, PhD, co-author of the new study, says that collecting weight measurements over a full year helped the researchers obtain accurate, real-life results—and, in doing so, helped show that holiday weight gain may be subtle, but that it really does happen.

“In past studies, results have been self-reported, or people would come into a facility to be weighed,” says Wansink, who is director of Cornell’s Food and Brand Lab and author of Slim by Design. “That means people could fib or change their behavior because they know they’re being monitored.”

The participants in this study also knew they were being monitored, but they didn’t know over what period of time or for what reasons—and measurements were taken when they weighed themselves daily, which they would have been doing anyway. “In that sense, we were getting behavior that was much more natural,” Wansink says.

Wansink says that, for people in the northern hemisphere, weight gain in the fall and winter is likely a combination of holiday foods and colder temperatures, which can lead to less outdoor activity.

“The weather may explain the gradual increase, but we also see these spikes that start about a week before the holiday and peak a few days after,” he says. “To me, that suggests that the holidays themselves aren’t the problem—it’s more the ramping up beforehand and all the Halloween candy or Thanksgiving leftovers or Christmas cookies you're eating afterward.”

The authors admit that the study participants were probably more engaged in weight-loss efforts than the general population—they’d purchased this scale and used it every day, after all—but they say the findings still provide insight that everyone can take to heart.

Wansink’s advice? “Instead of a New Year’s resolution to lose weight, have an October resolution not to gain too much weight in the first place. Then you won’t have to worry about five months of struggling,” he says.

That doesn’t mean you can’t celebrate special occasions or indulge in your favorite treats, either. "There’s nothing wrong with the holiday itself, but the key is to keep your eating to the holiday—not to the holiday season," he says. "You’re going to be in a lot better shape if you keep what happens on Thanksgiving to one day, rather than stretch it out for a week before and a week after."

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