Instead of making a New Year’s resolution to diet and exercise after you’ve indulged over the holidays, it’s probably wiser to make a vow to prevent holiday weight gain—starting in October. That’s the message from a new study of 3,000 people from around the world, which found that on average, people gain about 1 or 2 pounds during national holidays. And in general, it takes them about five months to burn it off. The study was done by Tampere University of Technology in Finland and Cornell University, and was published in the New England Journal of Medicine.

“Once we hit the first week of October in the U.S., weight starts going up very slowly, and it peaks right after New Year’s,” says Brian Wansink, Ph.D., a co-author of the study and a director and professor at the Food and Brand Lab at Cornell University. “Then it starts tracking down, but doesn’t hit the bottom until about mid-to-late-September.”

The study involved people from Germany and Japan as well as the U.S., and the findings were consistent from country to country, Wansink says. People indulging in sweet potato pie and turkey for Thanksgiving in the U.S. gain just as much weight as those downing rice dumplings and mochi balls during Golden Week in Japan. “Your lettuce-eating vegan is gaining the same as your rib-eating neighbor,” Wansink says. 

A More Accurate Assessment

Unlike some other studies that looked at holiday weight gain patterns, this one didn't rely on self-reported weight changes or in-person weigh-ins. Instead, it used data gathered from a smart scale the participants already owned, the WS-50 from Withings, a company that makes health gadgets that are WiFi- and Bluetooth-enabled.

When consumers set up the WS-50, they can pair it wirelessly with a smartphone app, which collects not just weight but also other information such as names, birth dates, email addresses, photos, and locations. But according to Withings’ privacy policy, that data can also be transmitted to the company unless consumers elect to opt out of sharing it. (And if they do, they might not be able to use all the features of the product.) Withings then provides some of information, anonymized, to researchers for projects such as this one. 

Having that kind of data allowed the researchers, one of whom is a Withings employee, to get a more accurate picture of weight fluctuations over time. “The study subjects can’t fib, they can’t tell you the weight they wish they were, they can't skip coming to the lab for weigh-ins,” Wansink says. “You’re looking at actual measurements of real people.”

Reality Check

A pound or two may not sound like a big deal. Wansink says the people in this study may represent an already healthier group. “These people are very self-aware types who like technology and clearly have enough money to buy a $150 scale and have WiFi,” he says. “In fact, I'd say they're probably in much better shape than the typical person. So if even the most motivated, vigilant groups of people are gaining weight and not losing it right away, then the average person is almost assuredly more likely to gain a lot more over the holidays and take a lot longer to lose it.”

You don’t have to take all the fun out of the holidays to minimize holiday weight gain, though. The trouble isn’t with holiday meals, per se. “You can have a great Thanksgiving dinner, but that doesn't mean you have to end up eating cookies for the whole week before and the whole week after,” Wansink says. “To not gain that weight in the first place means you’re not going to have to spend five months trying to lose it.”