College freshmen beware -- the "freshman 15," the eating binge long speculated to pile on 15 pounds during the first year of college, could be real. And the extra weight may be hidden in that extra bagel you grab in the dining room.

According to a new study by Cornell University researchers, college freshmen gain an average of 4.2 pounds just during their first 12 weeks on campus.

"Significant weight gain during the first semester of college is a real phenomenon, with breakfast and lunch at all-you-can-eat dining facilities accounting for 20 percent of the weight gain," said David Levitsky, a professor of nutritional sciences and psychology at the university.

Evening munchies, extra snacks on the weekends, and easy access junk food also add to the freshmen's extra pounds.

Levitsky presented the findings July 16 in Groningen, the Netherlands, at the annual meeting of the Society for the Study of Ingestive Behaviors, an international group of researchers studying eating and weight.

The research team speculates that the phenomenon mimics that of the obesity epidemic among Americans -- a relatively small increase in calories each day or week adds a significant amount of weight over the years.

Researchers assessed the weight gain of 60 Cornell first-semester students -- 85 percent of them female. The volunteers were weighed at the beginning and end of their first 12 weeks of college. Each filled out a questionnaire about eating, exercise and sleeping habits.

The freshmen, on average, gained about 0.3 pound per week, which is almost 11 times more than the weekly weight gain expected in 17- and 18-year-olds and almost 20 times more than the average weight gain of an American adult.

"American adults gain about 8 grams [about one-fourth of an ounce] a week, a rate of increase that is considered an epidemic by many as it easily leads to obesity," Levitsky said.

The college freshmen in the study gained an average of 158 grams (about 5 1/2 ounces) a week. That's the equivalent of ingesting about 174 more calories a day than energy expended, and the approximate calorie equivalent of two apples or a plain bagel.

"This amount represents a relatively small change in behavior, yet it has enormous cumulative consequences on weight," Levitsky said.

He said that although all-you-can-eat dining halls may be effective for recruiting students, the food bars may be responsible for much of the weight gain we see in freshmen. He said various studies show that humans tend to eat the amount of food they are served, and when students take large portions, they are apt to consume them.