But she said the results could also mean that people were just eating far more calories than they could burn off, even with all that physical activity.
"If you think about going for a run, if you run for 30 minutes and you run three miles during that time, you burn about 300 calories. Well, one piece of pumpkin pie without anything on it is about 300 calories," Cooper said. "So, it's really easy to eat all those calories that you burn during exercise and then some."
Exercise also boosts appetite, which can lead to even more overeating.
Cooper said that means there really is no substitute for moderation during the holidays, a time when foods are much more likely to be loaded with fat and sugar and hidden calories.
Despite the disappointing results, one expert said the study shouldn't be an excuse for people to abandon their workout routines over the next few weeks.
"Exercise has numerous benefits beyond just regulation of weight," said Joy Dubost, a nutritionist and spokesperson for the Academy of Nutrition and Dietetics.
The study found that exercisers may have maintained an advantage over non-exercisers: Their blood pressure tended to stay lower through the holiday hustle.
Dubost thinks that the problem with the holidays isn't just a big meal here or there, it's a mindset of indulgence that people tend to adopt between now and the end of the year.
"Typically what happens on Thanksgiving Day doesn't necessarily just stay for that day. It tends to trickle into an eating pattern that can stay with you through the holiday season," Dubost said.
"Then you step on the scale and it's gotten away from you," she added.
The study was published recently in the European Journal of Clinical Nutrition.