The finding comes from researchers from Finland, the U.S. and France, who followed the weight change of nearly 3,000 people in the United States, Germany and Japan over a 12-month period.
In all three countries, holidays were a clear recipe for weight gain.
Compared with their minimal annual weight, people in the U.S. added 0.7 percent to their weight – about 1.32 pounds, on average -- during the Christmas to New Year holiday season. In Germany, the comparable gain was 1.76 pounds. In Japan, participants hit their heaviest weight during Golden Week, a string of holidays in the spring, when people were more than a pound heavier on average than earlier in the year.
The chart above shows the average weight of American participants in orange. Americans tended to fall to their lowest weight in October and November, then pack on pounds around Thanksgiving and Christmas. Their weight then slowly fell throughout the summer and early fall. As the researchers note, about half of the weight Americans gained was lost again shortly after the holidays, but the other half remained into the summer months.
The Germans, shown by the blue line, gained significantly more weight at Christmas, and also saw weights rise around Easter. In Japan, Golden Week was when people are at their heaviest.
For those who don’t have issues with their weight, winter is not a bad time to pack on a little more insulation. But the researchers advise those who might struggle with their weight to plan ahead. Since October tends to lift off into rapid weight gain, and it’s easier to keep weight off than lose it, they say you might want to go ahead and make any weight-related New Year’s resolutions this month instead.