Contrary to the belief that people who burn a lot of calories are less vulnerable to gaining weight, a new study finds that they and slow-burners alike tend to put on kilograms during the sweets-filled holiday season.

"This idea of regulating body weight by being a very active individual who exercises a lot is not being supported by our study," said Dale Schoeller, a professor at the University of Wisconsin and the senior author of the study.

"That doesn't mean you shouldn't exercise," he said, "because there are tremendous health benefits from being physically active and having a high energy expenditure."

Schoeller's team collected information on body size from 443 middle-aged, mostly overweight people in September and October of 1999, and again after the holidays in January and February of 2000.

At the beginning of the study, the group measured the total amount of energy people used through a technique called "doubly labelled water", which involves drinking water tagged with oxygen and hydrogen atoms that are slightly different to those usually found in drinking water.

The researchers measured over two weeks how much of the labelled hydrogen and oxygen was passed through urine, and then calculated how much of the remaining labelled oxygen had been used to burn calories.

Total energy includes everything a person burns up - even while sleeping, watching TV, exercising and walking around.

The measurements taken in the autumn also revealed how often people were physically active.

At the end of the study, men had gained close to 907g and women a little over 454, equal to about a 1% gain in body weight.

People who burned the most calories in a day and those who were most active were just as likely to put on weight as those who used fewer calories.

"You'd think people with a higher physical activity level would be protected from holiday weight gain," said Susan Racette, a professor at Washington University School of Medicine, who was not involved in the study.

Presumably, the holiday parties, pastries, and religious feasts caught up with them.

It could also be that people were less active during the holidays, Racette said.

The researchers did not track how much people ate or how much they exercised during the season.

Schoeller said he would have expected that the high energy users would have been less affected because they should have an easier time compensating for the extra calories through more exercise or eating less later on.

For instance, if a Christmas dinner adds 500 calories to a person's daily energy needs, that's only a 17% increase for someone who burns 3000 calories a day, compared to a 25% increase for someone who uses 2000 calories.

"This extra 500-calorie meal would be a smaller part of their expenditure and therefore easier to compensate for than someone with a low energy expenditure," Schoeller said.

"It's not the case," he added.

A study published a decade ago by Jack Yanovski, of the National Institute of Child Health and Human Development, found that Americans gain about 450g during the holidays.

In an e-mail, Yanovski said the latest results "confirm the importance of the holiday interval from Thanksgiving to Christmas for weight gain. Further studies are needed to understand how to prevent weight gain during this vulnerable time of the year."

Schoeller said that the study backs up the idea that food - not exercise alone - is important in weight control.

"Obesity prevention built around physical activity without addressing food intake is not likely to succeed," he said.