Registered Dietitian Spills the Beans on Food Sensitivity Testing

Tamara Duker Freuman, M.S., R.D., C.D.N.

“The more patients of mine who show up having used a food sensitivity test kit—and are following restrictive diets in an effort to avoid any foods the test indicated they cannot tolerate—the more I have come to believe what a confusing distraction such tests have become in the pursuit of actually helpful and actionable answers.”

by Tamara Duker Freuman, M.S., R.D., C.D.N., self.com ¹

As a dietitian who works in a gastroenterology practice, I know that plenty of my patients find that certain foods don’t agree with them. It’s my job to help them figure out which ones. You’d think, then, that I would embrace the emergence of food sensitivity testing kits that identify food intolerances as a tool in my quest to help patients feel better. But the opposite is true.

Chances are, you’ve heard about food sensitivity test kits somewhere.

Maybe you’ve seen these tests advertised on social media, or through someone in your life who sees alternative health practitioners like a naturopath or chiropractor (through they’re also sometimes used by allopathic doctors). These tests generally require a blood draw, finger stick, or a drop of dried blood, while some use saliva or hair follicles. Some of them can only be ordered by licensed health care providers (which includes medical doctors or dietitians) and others can be ordered online and sent directly to your home. I’d like to share a typical patient experience when it comes to these kits based on what I’ve observed in my practice.

By the time a patient arrives at my office, they’ve already received test results that suggest a sensitivity to several foods—sometimes up to two dozen foods or more—many of which are currently part of their weekly diet staples, and that often include difficult-to-avoid ingredients like canola oil or yeast. In my experience, the results invariably suggest a sensitivity to gluten, dairy, and soy—I can’t remember seeing or being told about results that didn’t.

They tell me that initially they panicked about how they could possibly eliminate all of these foods and continue on with normal work and social commitments. But they were committed to giving it a try, so they’d dive in and spend a week or two preparing everything they eat from the foods they don’t feel like they have to avoid, like, for example, plain chicken, a handful of assorted vegetables, and rice. Sometimes they end up feeling better, whereas other times they don’t. (Certainly, if something they were eating regularly was bothering them initially, cutting almost everything out was likely to have swept up the offender in the process!) Regardless of how they feel, however, they soon realize they can’t keep up this highly restricted diet—and that’s when they arrive at my office. They’re confused about which of these foods—if any—is actually bothering them, and have no idea how to figure that out.

What happens next can vary. In the best case scenario, patients are willing to try to start over with me.

If this is the case, I’ll rewind to the beginning, review their history of issues so I can assess them without any preconceived notions about food tolerance. It seems to frustrate the patient, who has already spent a good deal of time and effort and emotional energy (and some money) trying to get to the bottom of a suspected intolerance only to not have answers that satisfy them or solve their problems. And I get frustrated, too. I want to spend the bulk of my time with a new patient listening to their story, taking a detailed food history, asking questions, reviewing medical records, and explaining my recommendations for next steps, not explaining misinterpreted or misleading test results.

But the worst case scenario is, in my opinion, that patients are unable to let go of the notion that this laundry list of foods indicated by the sensitivity test kit is somehow problematic for them.

They assume they still feel lousy not because they aren’t actually intolerant of the foods they eliminated, but rather because they haven’t yet eliminated enough foods. I’ve seen this happen more times than I can count, and when I’m unsuccessful at convincing my patient that these tests can be relied on to identify their problems, I’ve watched helplessly as my patient disappears down a rabbit hole of food restriction and avoidance that can, for some people, lead to disordered eating.

Let me explain a bit about how food allergies and intolerances work, and how these tests purport to work, so you can understand why I wish my patients never went down this path in the first place.

Let’s start by going over some possible reasons why you might consistently not feel well after eating. As the American Academy of Allergy, Asthma, and Immunology explains, a food intolerance (also sometimes called a sensitivity) takes place in the digestive system. It happens when you’re not able to break down food you eat. This can be caused by enzyme deficiencies, sensitivity to a food, or a reaction to naturally-occurring food chemicals. Typically people with an intolerance or sensitivity can eat these foods in small amounts without experiencing problems. A food allergy on the other hand, involves the immune system. If you have an allergy to milk, your immune system, whose job it is to defend and protect your body, experiences the milk as an invader or allergen. In response, your immune system produces antibodies called Immunoglobin E (IgE). These antibodies travel to cells and cause an allergic reaction, like something on the skin (hives, itchiness, swelling), gastrointestinal symptoms (vomiting and diarrhea), and even anaphylaxis. One important distinction between an intolerance and an allergy is that with an allergy, eating a tiny amount of the food can cause a serious, sometimes life-threatening reaction.

If you suspect you’re adversely reacting to certain foods, an allergist may measure blood levels of IgE antibodies to determine whether food allergy is likely. If you suspect you have the autoimmune disorder celiac disease, there’s a blood screening recommended (IgA-tTG) to start the diagnosis process. But without any evidence of an immune system response to foods, it’s likely that you’re looking at a food intolerance instead. There are objective, scientifically vetted hydrogen breath tests that diagnose food intolerances resulting from bacterial overgrowth in the small intestine and poor digestion of certain sugars—like lactose, fructose, or sucrose—but other food intolerances ideally should be identified through subjective measures: namely, closely monitored elimination diets followed by reintroducing a food to see if the reaction is reproducible.

If food intolerances are determined by breath tests or elimination diets, what do home test kits measure?

Whereas food allergy blood tests measure IgE, an antibody that attacks foreign proteins that produces an allergic response, many food sensitivity test kits measure Immunoglobulin G (IgG) antibodies, which we develop in response to certain foods. As a 2018 article in the journal Allergy and Clinical Immunology: In Practice explains, these tests likely measure IgG antibodies reliably. The catch is that the presence of IgG antibodies doesn’t in itself indicate an intolerance. In fact, as the article says, although “the measurement of IgG to foods is promoted to diagnose ‘food sensitivities’…the production of IgG antibodies to foods is a normal immunologic phenomenon. IgG antibodies to foods are found in virtually all healthy individuals.” The development of IgG antibodies “has specifically been linked to the development of food desensitization or tolerance.” The article goes on to state that

European Academy of Allergy and Clinical Immunology, the American Academy of Allergy, Asthma, and Immunology, and the Canadian Society of Allergy and Clinical Immunology have all issued papers, statements, and endorsements that positive test results for food-specific IgG are to be expected in healthy adults and children.

“IgG is a memory antibody that we develop after exposure to various things, including foods,” David Stukus, M.D., associate professor of pediatrics in the division of allergy and immunology at Nationwide Children’s Hospital, fellow of the American Academy of Asthma, Allergy, and Immunology, and fellow of the American College of Allergy,, Asthma and Immunology, tells SELF. Stukus explains that when you measure IgG levels in the blood, “you’re seeing what people have eaten in the past, and higher levels suggest foods that are eaten more than others.” The problem arises, according to Stukus, when patients or providers misinterpret their results as findings of an intolerance response—particularly since IgG levels are actually a marker of tolerance rather than intolerance.

Some companies that make food sensitivity test kits claim to be able to diagnose food sensitivities that cause delayed or chronic adverse reactions. The idea being, according to the 2018 article, that “IgG food antibodies could lead to these conditions include chronic inflammation perhaps through the formation of immune complexes.”

However, as a 2017 article in Immunology and Allergy Clinics of North America explains, where some studies have indicated that dietary modification based on IgG testing leads to symptom improvement, these studies “are likely to be biased because of the placebo effect, and more rigorous studies are clearly needed to support its use.”

If you find yourself suspecting you have a food intolerance, the thing to do is keep a detailed food and symptom log for two full weeks. Write down the time of everything you eat—with details down to the brand when appropriate—and the time of any adverse symptoms you may experience. Bring this information to a reputable registered dietitian—ideally one who specializes in food allergy or gastrointestinal issues and doesn’t sell any supplements—so that they can help you identify the common threads among likely trigger foods or meals. This exercise will most likely yield a sane, manageable diet trial that you can undertake toward identifying the precise nature of your symptoms.

Tamara Duker Freuman is a New York–based dietitian whose clinical practice focuses on the dietary management of digestive and metabolic diseases. While she works with patients who have a variety of health issues, her expertise is in helping identify the many possible causes of gas, bloating, diarrhea, and constipation, and helping patients achieve symptom control and improved quality of life. Because of this expertise, she has been called “The Bloated Belly Whisperer,” and she liked the name so much she made it the title of her first book.