IgG tests promise to reveal food sensitivities. But are they science or science-ish?
Viola Dessanti has just gotten back the results of her young daughter’s IgG test—a blood test that looks for food sensitivities. “I have mixed feelings about it,” she says.
Dessanti’s naturopath shared the results with her a few hours before she spoke to Healthy Debate. Her two-and-a-half-year-old daughter had elevated antibodies for three foods, and was borderline for six. Dessanti, who hopes the test will help uncover food triggers for her daughter’s asthma, is worried about its limitations. But she’s happy they did it.
“I know full well that it isn’t definitive,” she says. “But at the same time, when your kid suffers from something life threatening, you’ll do anything to get even just a little bit more insight into what will make it better. Anything that I can do to give me a little bit more information, more tools to manage this, I’ll take it.”
She plans on cutting out the flagged foods and then reintroducing them, to see if they are causing some of her daughter’s flare ups. She sees it as part of a broader care plan for her kid, one that also includes inhaled steroids, keeping a detailed diary of symptoms and looking for other potential triggers, like dust.
The public seems sold on the promise of IgG tests: they’re widely available and commonly used. Most people, like Dessani, get them through naturopaths, many of whom advertise the ability to treat allergies and requisition IgG tests on their websites. For a cost of hundreds of dollars—Dessanti paid $300 for hers, and prices go up to $700—they’ll test for sensitivities against more than 100 foods.
The tests have both contributed to and benefited from the wave of interest around food sensitivities—6% of Canadians, for example, believe they have non-celiac gluten sensitivity. They’re advertised as helping a wide variety of diseases. One major Canadian test, Rocky Mountain Analytical, claims on its website that sensitivities have been linked to migraines, irritable bowel syndrome, mood disorders and weight gain.
“[IgG tests are] very popular,” says registered dietitian Wendy Busse. “There are so many symptoms and difficulties that are very hard to diagnose and treat, and people want answers. Food sensitivity testing comes back with very specific answers.”
But are they the right ones?
The evidence around IgG tests
Linda Kirste is an allergy specialist with dietitian and physical activity services at Health Link B.C., a service that lets the public connect with a dietitian for free over the phone or by email. She often speaks to families who have had IgG testing, many times because of concerns about their children or gastrointestinal issues. “It’s often an ongoing concern by the parent of some kind of unresolved health issue,” she says. Sometimes they’ve also had IgE tests—the standard blood test for allergies.
Many people who call Kirste think an allergy encompasses both an anaphylactic reaction, like you’d have from a peanut allergy, and an intolerance, which can cause bloating, stomach cramps and fatigue. In fact, they’re two completely different things: food allergies are an immune-system response, and food intolerance – often also called a sensitivity—isn’t.
That’s a problem for IgG tests, because IgG is an immune response. And in studies on lessening allergic reactions to things like milk or peanuts, researchers have found that IgG levels go up as the severity of an allergic reaction goes down. It’s thought that we produce the most IgG antibodies to foods that we eat regularly—“like getting a constant booster shot,” says allergist Stuart Carr. That’s why common foods, like dairy, wheat and egg, will often show up positive on an IgG test.
Kirste says that message resonates with her clients. “I’ll tell them that IgG may simply indicate that the food is in the diet. And we know that in children who are outgrowing an allergic condition, IgG goes up, and IgE goes down,” she says. “Then the light bulb goes on—they get it.”
Across the country, Carr is having similar conversations. He says he often has people who have had IgG tests get referred to him – and he has to explain to them that they’ve paid big bucks for something that offers no useful information. “When I see a patient come into my clinic, and they say we had this [IgG] test done, they will reach in their bag and try to hand me this booklet of results,” he says. “I’ll say, I don’t need to see that, and explain why we can ignore it.”
Carr authored a position statement for The Canadian Society of Allergy and Clinical Immunology released in 2012, that concludes there is no research supporting using these tests to diagnose or predict adverse reactions to food. It was in line with previous statements from The American Academy of Allergy Asthma and Immunology and the European Academy of Allergy and Clinical Immunology.
And a more recent review on allergy management and diagnosis published this fall in the CMAJ also expressed concerns about them. “Food-specific immunoglobulin G (IgG) testing is being increasingly used to identify food ‘sensitivities,’” it reads. “… In fact, food specific IgG is to be expected, marking the presence of exposure and tolerance to a food.”
The fact that IgG tests test for dozens of foods is also concerning. Even IgE panel tests—which allergists and doctors use to test for immune responses—aren’t very accurate, and return a lot of false positives. One review of 125 kids found that 80% to 100% of the foods that IgE tests flagged could be safely reintroduced into their diets. Another study looked at over 700 oral food challenges – where a person eats a small amount of a suspected allergen under medical supervision—and found that only 19% of patients reacted. “It’s important for people to appreciated that an IgE test is not synonymous with a diagnosis,” says Kirste.
That’s why allergists also use a history of reacting to foods to help with the diagnosis, and why the gold standard for allergy testing is an oral food challenge. Choosing Wisely Canada and the Canadian Pediatric Society recently named IgE panel tests without a medical history as one of the tests that are commonly used and often inappropriate.
Problems with IgG test
If IgG tests don’t work, there’s the obvious concern that consumers are wasting their time and money. Dietitians also worry that the tests could throw your diet off-kilter. That’s especially important in children. There is evidence that kids who have had their diets limited by food allergies can be susceptible to poor growth and nutrient deficiencies—and it makes sense that restricting a child’s diet due to suspected intolerances or sensitivities could have the same effect. In extreme cases, it can lead to 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, to nurture healthy eating patterns,” says Kirste. Disrupting those could lead to unhealthy eating patterns, and increase their risk of developing eating disorders.
For people who are worried they might have an intolerance to a food, there’s a better (and cheaper) way to look: An elimination diet. “You keep a food diary for four to six weeks, and write down whatever symptom you’re worried about—because most people have recall bias,” says Carr. “And then if you identify a food or two potentially from the diary, you take it out of the diet for two or three weeks, you see if those symptoms improve. You can sort out almost any food intolerance with a little bit of detective work.”
And they should also keep in mind that the problem might not be food related at all. Because of all the buzz around restricted diets, it’s tempting to think an intolerance 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.”