Taking a swim in cold water may be invigorating, but it could increase appetite enough to cause weight gain, U.S. researchers said on Wednesday.

The study may help explain why it is more difficult for some people to lose weight by swimming as opposed to other forms of exercise.

The University of Florida team tested how many calories were burned by 11 volunteers while exercising in warm water and in cold water. They ate 44 percent more calories after exercise in cold water than in warm water, the researchers found.

“It’s possible that individuals who exercise in cooler water may have an exaggerated energy intake following exercise, which may be a reason why they don’t lose as much weight,” said Lesley White of the College of Health and Human Performance, who led the study.

“So it may not be the exercise itself that causes the problem because you can match the exercise energy expenditure; rather it’s the increased eating after the exercise is over.”

That is not to say exercising in water is a bad thing.

“Water exercise is an excellent activity for many people, particularly those with joint disorders, thermal regulatory problems and balance or coordination difficulties,” she said in a statement.

“However, an earlier study reported that women who swam did not lose as much weight as those who jogged or cycled.”

Writing in the International Journal of Sport Nutrition and Exercise Metabolism, White and colleagues said they had their student volunteers exercise on a stationary bicycle submerged in water for 45 minutes, in either cold water at 68 degrees F (20 degrees C) or warm water at 91.4 degrees F (33 degrees C).

They used, on average, 517 calories cycling in the cold water and 505 in the warm water, compared to 123 calories while resting.

The students were then put into a room with food.

“We found that during the recovery period, when the subjects had access to an assortment of foods, that significantly more calories were eaten after exercise in cold water compared to exercise in warm water or at rest,” White said. Body temperature might also affect appetite, she added.