TORONTO -- A new study suggests more than half of Canadians, especially those with health conditions, are worried the foods they're buying are not what labels claim -- and preventing falling victim to such scams can be difficult, experts say.

In an online survey conducted by researchers at Dalhousie University, 63 per cent of respondents said they were concerned about the widespread practice known as food fraud. Notably, worries about counterfeited food products coming from Canada were even greater in those study participants with food intolerances.

That's likely because the fallout for someone with allergies eating a mislabelled product can be severe, says lead researcher Sylvain Charlebois.

He calls food fraud "the big elephant in the room."

"People are aware of the problem. They just don't know how to deal with it," Charlebois said.

Ingredient lists are lifelines for people with food allergies, says Beatrice Povolo, the director of advocacy and media relations for Food Allergy Canada, a non-profit organization advocating on behalf of people with food allergies.

"They count on that to be accurate and truthful and complete in order for them to make a decision of whether that would be a suitable product or not," she said, adding deliberate ingredient substitutions are not on the organization's radar at the moment.

Olive oil is the perfect example of a product that frequently contains unlisted ingredients, according to Larry Olmsted, author of "Real Food Fake Food." Sometimes it'll be watered down with peanut or soy oil, he says, and both are allergens.

The Canadian Food Inspection Agency receives an average of 40 complaints annually from consumers about potential food misrepresentation, spokeswoman Lisa Murphy wrote in an email, and it investigates each case.

The CFIA has studied the scope of the issue and determined concerns include short-weighting products, substituting ingredients, and making false and misleading claims about products.

It also has several programs to monitor certain types of food for fraudulent products, such as olive oil. Between 2006 and 2007, more than 45 per cent of tested samples did not meet the country's criteria for the product, according to a 2013 presentation by CFIA before a European Commission workshop on olive oil authentication. By 2012 to 2013, that number dropped to more than 30 per cent.

Food fraud is a financially motivated practice, Charlebois said, and is often done to increase the price an item will sell for or lower the cost of making it.

Seafood is the most vulnerable food group, he noted, because it's difficult to track where those products came from and hard to distinguish between fish species visually once it's a fillet on a store shelf.

That can be problematic for people allergic to certain shellfish who, for example, may order a dish like lobster-filled ravioli that's really composed of a mixture of cheaper shellfish like shrimp.

Until technologies being developed to help consumers validate food labels on their own become available, Charlebois said shoppers and diners must rely on asking questions about vendors and the origin of foods.

Olmsted said one good practice is to purchase food that isn't heavily processed as it's then harder to hide unexpected ingredients. Buying coffee beans rather than grounds, for example, makes it less likely the product will contain charcoal, paper or sawdust, he said.

"Buying as close as you can to the natural form generally helps you," Olmsted said.

The Dalhousie University survey was conducted for three weeks in January among nearly 1,100 adult respondents living in Canada for at least one year.

The polling industry's professional body, the Marketing Research and Intelligence Association, says online surveys cannot be assigned a margin of error because they do not randomly sample the population.