A new study has confirmed what your waistband has told you all along: You gain weight during the holidays.
It also concluded that people who weigh themselves frequently seem to lose those extra pounds faster.
The trend was seen in 1,781 Americans, 760 Germans and 383 Japanese, all of whom used WiFi "smart scales" over a one-year period. They had agreed to let the scale manufacturer, Withings, use the data for research purposes. Age, gender, height, country and time zone were collected as part of the registration process.
That system avoided limitations of previous weight studies, where people often lie when reporting their weight or they may eat differently knowing that they have to report to a place once a week to be weighed. Under this system, all weights were automatically recorded.
Within 10 days of Christmas, the average weight increased 0.4 percent among Americans and 0.6 percent among the Germans. For the Japanese, a 0.3 percent increase came during Golden Week in May, which includes an aggregation of four holidays.
For a 150-pound person, that's less than a pound.
But one of the authors of the study published in the New England Journal of Medicine, Dr. Brian Wansink, told Reuters Health in a telephone interview that the increase was so low because the people using the scales were unusual.
The devices cost around $150 and people willing to pay that much are probably more motivated than the average holiday reveler to keep their weight down and lose whatever they've gained.
"We're looking at people who are a little richer, maybe a little better educated, a little more health-conscious," said Wansink, professor and director of the Food and Brand Lab at the Dyson School at Cornell University.
It demonstrates that even the hyper-vigilant gain weight around the holidays, he said.
Previous studies have shown that Americans typically gain 3 to 5 pounds over the holidays.
Increases of 0.2 percent were also seen among Germans during Easter and among Americans during Thanksgiving.
For Americans, the upward tick on the scales began around the beginning of November and peaked around New Year's Day. For Germans, it began in late November and peaked a little after New Year's Day. The Japanese New Year's spike occurred around the same time as the German spike.
Dr. Wansink said the results also reveal that people who weighed themselves most often lost the extra weight more efficiently.
"People who weigh themselves three or four times a week had lost the weight they'd gained within a month of the holiday," he said. "The rest of the group typically took five months to get back to their pre-holiday weight."
Doctors can urge their patients to exercise more self control over the holidays, the researchers said. But it might be better to remind them that those pounds can persist "until the summer months or beyond."
"Of course," they added, "the less one gains, the less one then has to worry about trying to lose it."