Men with bigger wallets have bigger waistlines, Canadian study finds

"Women aren't spared by this correlation, but results are ambiguous," says Dumas. "However, women from rich households are less likely to be obese than women of middle or lower income."

Dumas used data from the 2004 Canadian Community Health Survey (CCHS). This provided access to information from some 7,000 adults aged 25 to 65. Dumas' research is unique because she took into consideration the sex of individuals as well as their body mass index (BMI) to differentiate the overweight from the obese.

"Many epidemiological studies have established that the odds of being overweight or obese decrease as family income increases," says Dumas. "But we don't know why this relationship is inverted for Canadian men. According to the CCHS, the richer they are, the fatter they are."

So why are rich men and poor women more likely to be obese in Canada? Dumas researched all existing literature and concluded a socioeconomic hypothesis could only explain the link of obesity and income for women. Yet no hypothesis could explain the phenomenon observed in Canadian men.

"Since the 1980s, the greatest increase in obesity levels has been among rich Canadian and Korean men," says Dumas. "We still can't explain why." According to Dumas, one possible explanation is dining out. "Canadians love restaurants. And people who regularly eat out have no control over what they eat. They also tend to eat more calories and consume larger amounts of alcohol."

Too many restaurant meals, combined with a decrease in physical activity, is another possibility. "There are obviously various factors at play: we still haven't empirically proved them," says Dumas.

The 2004 CCHS found 23.1 percent of Canadians 18 years or older -- about 5,5 million adults -- are obese. By 2030, according to the World Health Organization, 2,3 billion people will be overweight and 700 million of will be obese.