TORONTO — Canadians who have packed on a few too many pounds are at risk of tipping the scales towards obesity over time, rather than shrinking their waistlines, a Statistics Canada study suggests.

Almost one-quarter of Canadians who were overweight a decade ago had become obese by 2002-03, said Thursday's report by the government agency, citing the latest available figures.

"What we found was that the trend is definitely towards weight gain," Christel Le Petit, a senior analyst with Statistics Canada, said from Ottawa. "So if we look at the overweight people, for example, we found that 24 per cent of them became obese . . . while only 10 per cent went back to a healthy weight.

But it was not just already-tubby Canadians who added to their waistlines: one-third of people who started out in the normal weight range were overweight eight years later.

Men were more likely than women to go from a normal weight to overweight. By 2002-03, 38 per cent of the men had become overweight, compared to 28 per cent of the women.

However, women were more likely to go from being overweight to being obese. By 2002-03, 28 per cent of overweight women were obese, compared to 20 per cent of the men.

"So Canadians have been gaining more weight than losing it over the last eight years," Le Petit said.

The study followed almost 11,000 Canadian adults aged 20 to 56 in 1994-95, checking on their weight status every two years.

At the time, 3.1 million men and 1.7 million women across the country were considered overweight. Eight years later, the study suggests, more than one million had joined the ranks of the obese - 600,000 men and almost 500,000 women.

Among those at greater risk of sliding into obesity are women, younger men and those of lower socio-economic status, Le Petit said.

"We found that younger adults, especially among men, were more likely to become obese," she said. "Men in their 20s were 2.5 times more likely to become obese than men in their 50s." The risk for young women was not as high.

Being rich or poor also seemed to make a difference to how much bulk Canadians carry.

"We found that having more money, being in those higher income categories, reduced your risk of becoming obese by about 40 per cent, and that was for both men and women," Le Petit said.

While the statistics can't offer reasons why, other studies have suggested a number of reasons that lower incomes equate to greater girth.

"Households with lower incomes, they have to balance a number of expenses - lodging and clothing and food," said Le Petit. "And healthy food tends to cost more, while foods that are high in fat and high in sugar tend to cost less. So, for those families it could be one of those trade-offs that they have to make."

Obesity experts say being overweight can have serious health consequences, including diabetes, heart disease, stroke and osteoarthritis.

Diane Finegood of B.C.'s Simon Fraser University, a scientific director of the Canadian Institutes for Health Research, said the trend towards greater obesity in Canada is not surprising, but social-cultural and biological factors linked to the problem aren't easy to change.

"If we grew up as a young person in a low socio-economic status circumstance, even if we are elevated in our . . . status as an adult, we still have a higher risk for developing obesity," Finegood said from Montreal, where she was attending a conference. "And if we grow up in a low socio-economic status, and we live that way as an adult, we have the greatest risk of developing overweight and obesity."

Vices besides food also seem to affect weight gain, the study showed.

Researchers got a bit of a surprise to see that men who smoked were more likely to end up obese, contrary to conventional wisdom that tobacco use makes people skinnier. But a deeper look into the data showed that many of the men had quit smoking during the study, and "that seems to be when they put on the weight," Le Petit said.

While the research did not include children, the authors note that having severely overweight parents significantly hikes the chances that a child's weight will balloon over time.