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Food sensitivities are blamed for everything from irritable bowel syndrome to mood disorders.BradCalkins/Getty Images/iStockphoto

Food sensitivities are blamed for everything from irritable bowel syndrome to mood disorders. And many of us are on special diets as a result – 6 per cent of Canadians, for example, believe they have non-celiac gluten sensitivity, according to the Canadian Celiac Association.

"There are so many symptoms and difficulties that are very hard to diagnose and treat, and people want answers," says Wendy Busse, a registered dietitian in Red Deer, Alta., who specializes in allergies. Food-sensitivity tests are a popular starting point – but experts caution they're not likely to give you useful information. Here's why.

What is a food sensitivity?

Food sensitivities are often confused with allergies, says Linda Kirste, a dietitian with HealthLink BC who focuses on food allergies. But an allergy is a specific response that involves the immune system – such as the anaphylactic reaction you'd get with a peanut allergy.

Food sensitivity, on the other hand, is a very broad term that includes most negative responses to food, including irritable bowel syndrome, migraines and weight gain. Mainstream medicine prefers to discuss food intolerance, which causes mostly digestive problems and isn't related to the immune system.

Are there tests for it?

IgG tests are marketed as a way of testing for food sensitivities. Most people order the blood tests, which cost hundreds of dollars, through naturopaths. The tests look for IgG antibodies – proteins created by the immune system – for more than 100 foods, ranging from dairy to seafood to specific spices.

Do these tests work?

The tests do measure IgG levels – but the idea that IgG levels are tied to food sensitivities isn't supported by the science. In fact, studies that looked at reducing allergic reactions in children for things such as milk or peanuts, researchers found that IgG levels went up as the severity of allergic reactions decreased. So it's actually seen as a sign a food is well tolerated.

Researchers believe that we produce the most IgG antibodies to foods that we eat regularly. "It's like getting a constant booster shot," says Stuart Carr, a pediatric allergist in Edmonton. That's why common foods, such as dairy, wheat and egg will often show up positive on an IgG test.

Carr authored a 2012 position statement for the Canadian Society of Allergy and Clinical Immunology that concludes there is no research supporting using IgG tests to diagnose or predict adverse reactions to food. Previous statements from the American Academy of Allergy Asthma and Immunology and the European Academy of Allergy and Clinical Immunology agreed.

What's the harm?

If IgG tests don't work, there's the obvious concern that they're a waste of time and money. Dietitians also worry that the tests could lead to poor nutrition. That's especially important in children. Research shows kids who have had their diets limited by food allergies can be susceptible to poor growth and to nutrient deficiencies, and restricting a child's diet due to suspected intolerances or sensitivities could have the same effect. In extreme cases, it can result in malnutrition.

More commonly, it can contribute to an unhealthy relationship with food. "We have an opportunity as parents to support children developing a healthy relationship with food and eating," says Kirste. Disrupting that could lead to unhealthy eating patterns, and increase their risk of kids developing eating disorders.

Are there other options?

For people who are worried they might have an issue stemming from certain foods, there's a better (and cheaper) way to find out: Try an elimination diet, under the guidance of a health-care provider. "You keep a food diary for four to six weeks, and write down whatever symptom you're worried about," Carr says. "If you identify a food or two from that, you take it out of the diet for two or three weeks, see if those symptoms improve. You can sort out almost any food intolerance with a little bit of detective work."

It's also important to keep in mind that the problem might not be food-related at all. With all the buzz around restricted diets, it's tempting to think a sensitivity is behind a wide range of issues, and that's not always the case. "There is a tendency to want to blame food," Busse says. "But I think it should be innocent until proven guilty."

A version of this story first appeared in Healthy Debate, an online publication guided by health-care professionals and patients that covers health policy and evidence-based medicine in Canada.