Obesity rates in Canada have tripled since 1985, with a disproportionate increase in the number of very obese Canadians, according to new research from Memorial University in Newfoundland.

Based on this “worrying” trend, it’s expected that about 21 per cent of Canadian adults will be obese by 2019, according to a study published in the Canadian Medical Association Journal.

Analyzing data from Canadian health surveys conducted between 1985 and 2011, researchers found that the overall obesity rate increased from six per cent to 18 per cent over the 26-year period, although numbers varied by province.

The biggest increases occurred among people with the highest body mass index, calculated from a person’s weight and height. Obesity is defined as a BMI of 30 or higher.

In the study, obesity levels were described as class I, II or III, with BMIs ranging between 30 and 40 or higher. The most significant rate of increase was noted in the class III obesity rate, which went up from 0.3 per cent in 1985 to 1.6 per cent in 2011.

“The more telling story was the disproportionate jumps in the higher obese classes,” said Laurie Twells, co-author of the study and an associate professor at Memorial University’s School of Pharmacy and Faculty of Medicine.

Although the percentage of highly obese people is small, “it’s a growing group of people with complex care needs, so that’s a group that we need to be worried about,” she told CTVNews.ca.

The study also found that obesity rates were lower in the West, especially in British Columbia, and higher in Atlantic provinces. The highest rates were found in New Brunswick and Newfoundland and Labrador.

Meanwhile, “the prevalence of normal-weight people in Canada is steadily decreasing,” the study says.

Because the analysis was based on self-reported heights and weights of survey participants, the result is likely an underestimation of obesity levels, although trends over the 26 years are accurate, the study says.

Obesity is a huge strain on the health care system, with annual costs estimated at between $4.6 and $7.1 billion, according to researchers. They note that obese people are at an increased risk of Type 2 diabetes, high blood pressure, cancer and sleep apnea, among other health issues.

Gaining weight, especially as you age, will not necessarily make you unhealthy, Twells said. The trouble is that more overweight people are entering the obese category, she said.

“You can be incredibly healthy being overweight, but the issue is that people don’t tend to stay there,” she said.

“We need to make sure that we keep on top of it, because the numbers are not going away.”

The latest study notes that it’s difficult to measure the effectiveness of obesity treatments and prevention strategies across the country because health services vary by province and territory.

Regardless of an individual province’s plan of action, it can take 20 to 30 years to see the impact of a policy change, Twells said.

Canada is not the only country battling the obesity epidemic. Expanding waistlines are contributing to rising health care costs around the world.

In the U.S., studies have estimated that 42 per cent of the adult population will be obese by 2030. Although a recent study published in the Journal of the American Medical Association suggested that prevalence of obesity has decreased by 43 per cent among young children, some epidemiologists say that data was taken out of context and that actual numbers are less impressive.

Either way, the Centres for Disease Control and Prevention has made it clear that overall obesity rates remain unchanged in the U.S.