Regularly drinking even as little as one can of pop a day could raise your risk of type 2 diabetes, new research reveals.

It's no secret that drinking too many soft drinks can lead to weight gain. But this study is the largest yet to look at the drinks' link to diabetes and a pre-diabetes condition called metabolic syndrome.

Researchers with the Harvard School of Public Health looked at 11 recent studies on the risk of diabetes and sugar-sweetened beverages -- which include soft drinks, but also bottled iced tea and fruit-flavoured drinks and flavoured waters. The studies involved more than 300,000 adults.

The researchers found that regularly drinking just one 350-millilitre serving of a sugary drink a day increased the risk of type 2 diabetes by 15 per cent, compared with those who consumed less than one sugary drink per month.

Drinking one or two soft drinks a day boosted the risk by 26 per cent.

As well, drinking one to two drinks per day increased the risk of metabolic syndrome by 20 per cent. Metabolic syndrome is the name for a group of five risk factors, such as high blood pressure and excess fat around the waist, that have been shown to increase the risk of heart disease, diabetes and stroke.

The study appears online in the journal Diabetes Care and will appear in the November print edition.

The researchers, led by nutrition researchers Vasanti Malik and Frank Hu, a professor of nutrition and epidemiology at HSPH, say their analysis shows the drinks are clearly linked to adult-onset diabetes.

"The association that we observed between soda consumption and risk of diabetes is likely a cause-and-effect relationship because other studies have documented that sugary beverages cause weight gain, and weight gain is closely linked to the development of type 2 diabetes," Hu said in new release.

Susan Whiting, a professor of nutrition at the University of Saskatchewan, who was not involved in this study but has researched soft drink consumption, says the results are surprising considering how many people regularly drink soft drinks.

"What surprised me is the quantity," she told CTV News. "One to two drinks a day, we might have thought that was almost a moderate intake and this study defined it as high."

Dr. Jean Pierre Despres, a professor at the department of sciences of food and nutrition at Laval University in Quebec City, says sugary drinks, which contain about 10 teaspoons of sugar each, are hard for the body to process.

"It provides the body with a big glycemic load, and makes the beta cells [in the pancreas] take a huge load," he says. "Eventually, they get exhausted."

Despres notes that cutting back on sugar-sweetened beverages is an easy way to lower the risk of diabetes

"With the epidemic of diabetes in this country, one simple step to minimize the risk is to drink water," he said.

Whiting would like to go further. She would like to see a tax on sugar-sweetened drinks, noting that when 2 litres of pop costs less than a litre a of milk, soft drinks are too cheap.

"We have a product that's inexpensive and easily obtained and we need a way to put some limits on its consumption," she says.

"Now we have evidence it affects the health of adults, so we do need to talk about it and hopefully, that talk leads to action."

But Refreshments Canada, the trade group representing beverage makers in Canada, disagrees, saying it is overly simplistic and misleading to suggest that reducing or eliminating sugar-sweetened beverages from the diet will lower the incidence of diabetes or metabolic syndrome.

"There is a critical flaw in the design of the studies used in this meta-analysis, in that the authors focus solely on the impact of one calorie source – sugar-sweetened beverages – on weight, rather than looking at all sources of calories," said Refreshments Canada's Justin Sherwood.

With a report from CTV's Avis Favaro and producer Elizabeth St. Philip