The good news for college students this holiday season is they can eat mounds of mashed potatoes and the weight they gain will disappear for most of them by the first of the year. The bad news is they will lose good muscle and keep the fat.

New research at the University of Oklahoma showed that college students who were normal weight before the holidays gained about a pound, then lost it by the time they returned to school in January. But, the same research revealed that the pound lost by students is not fat, but muscle, which led to an increase in the students’ overall percentage of body fat.

The news was even worse for students who were overweight before the holidays. They not only kept the extra weight, but added twice as much body fat by January as the normal-weight students.

“The way we interpret it is when they went home they simply weren’t working out and they weren’t walking to class. They are just vegging out on mom and dad’s couch, watching football games,” said David Fields, PhD and an assistant professor of pediatrics with the University of Oklahoma College of Medicine.

“If you’ve got this happening in a pretty active group of people, you can only imagine the effect in someone who doesn’t exercise much. I suspect it’s even more pronounced in groups who are older than college age.”

The research is part of a study looking at weight gain and health of college students.

Fields and doctoral student Holly Hull measured weight and percent body fat of 94 college students before Thanksgiving, right after Thanksgiving and at the beginning of the year when they returned to school. The students were freshman to graduate students and ranged in weight from skinny to obese.

Fields said students who were normal weight faired better than their overweight counterparts, but every student who gained weight during the Thanksgiving break retained fat.

Students who were normal weight gained less than 1 percent body fat while students who were overweight gained an average of 2 ½ percent body fat.

“I suspect probably what happened is the more normal weight people were more active. They walked around a little bit more; they stood up more. When they over ate, their bodies told them, ‘Hey Jim or Sue, you have to walk around more.’ We know that’s true in animals.”

Fields hopes to use the study’s results to attract more funding. Researchers want to include more students and measure more factors such as cholesterol and heart rate.