Food Sensitivity Tests: What They Can and Can't Tell You

Quick answer: Most at-home food sensitivity tests measure IgG antibodies, and allergy societies advise against using them to diagnose food allergy or intolerance, because IgG mostly shows that you have eaten a food. A clinician, a food and symptom diary and a supervised elimination diet are the usual ways to find out what bothers you.

If certain foods make you feel unwell, a kit that promises to name them from a finger prick is tempting. Before you spend money, or remove foods from your diet because of a report, it helps to know what these tests measure and what the doctors who study them say.

What a Food Sensitivity Test Measures

The tests sold directly to consumers usually measure immunoglobulin G (IgG), or the subtype IgG4, to a panel of foods in a blood sample. Some companies use other methods, such as hair analysis or cell-based assays. These are generally laboratory-developed tests. A STAT News report notes that they are not regulated by the FDA in the way approved diagnostic tests are, and that physician groups have advised against using IgG tests to evaluate food sensitivities for years.

What Allergy Societies Say

• European Academy of Allergy and Clinical Immunology (EAACI): a 2008 task force report was titled "Testing for IgG4 against foods is not recommended as a diagnostic tool." The AAAAI's Adverse Reactions to Foods Committee endorsed it in 2010 (document).
• AAAAI and ACAAI: the 2014 joint task force practice parameter on food allergy recommends against unproven tests, including measurement of allergen-specific IgG and cytotoxicity assays, for evaluating food allergy.
• Canadian Society of Allergy and Clinical Immunology (CSACI): its position statement says there is no body of research that supports using the test to diagnose adverse reactions to food or to predict future ones.
• NIAID-sponsored guidelines (2010): the expert panel advised against a group of nonstandardized tests for routine evaluation of IgE-mediated food allergy, including allergen-specific IgG4 and cytotoxicity assays, citing a lack of evidence that they have any value in diagnosis. See the AAFP summary.

Why a Result Can Mislead

• IgG is part of a normal response to foods you eat. A high level for a food generally reflects exposure and does not show that the food harms you. Insurer and clinical summaries also note that IgG results have not been shown to correlate with oral food challenges.
• A positive result can lead you to cut out foods that you tolerate, which can mean a more restrictive diet, nutrient gaps and more worry about eating.
• A negative result can falsely reassure. Someone with a true IgE-mediated allergy, who is at risk of anaphylaxis, may not have raised IgG to that food at all.

Allergy, Intolerance, Celiac Disease and Sensitivity

These terms are often mixed up. A food allergy is an immune reaction that can be serious. Food intolerances, such as lactose intolerance, involve digestion. Celiac disease is an autoimmune condition triggered by gluten and is diagnosed with specific tests while you are eating gluten. Food sensitivity is an informal word for symptoms that do not fit the others. Our guide to food intolerance vs. allergy explains how to tell them apart, and the celiac diet guide covers celiac disease.

What Does Work

• See a clinician. A doctor, allergist or gastroenterologist can ask about your symptoms and decide which tests, if any, are right. Many conditions cause symptoms that get blamed on food, including irritable bowel syndrome, inflammatory bowel disease, gallstones and ulcers.
• For a suspected allergy, use validated tests. The NIAID-sponsored guidelines say history, skin prick tests and allergen-specific IgE help identify suspect foods but are not diagnostic alone, and that a food challenge or a clear reaction history confirms the diagnosis. Never run a food challenge on your own.
• For celiac disease, ask your doctor how to test before you remove gluten, because testing is done while you are still eating it.
• For lactose and fructose, a doctor can arrange breath tests. These are generally the exceptions: one clinical review in Advisory Board notes that most other food intolerances have no validated biomarker.
• For other suspected intolerances, a supervised elimination diet is the usual approach: remove a food or group for a set period, then reintroduce them one at a time while you watch for symptoms. That article advises that a doctor or registered dietitian design and supervise it, and a VA clinician guide to elimination diets cautions about nutritional gaps and about people with eating disorders.
• Keep a food and symptom diary. It gives your clinician the data they need, and it costs nothing. See our guide to food diary apps.

If You Still Want to Take a Test

• Ask your doctor first, and bring the result to them rather than acting on it alone.
• Do not remove a food for good because of a report. If you decide to try removing it, do it with a clinician's plan and reintroduce it as directed.
• Never use a test to decide whether a food is safe if you have had a serious allergic reaction. Follow your allergist's advice.
• Be wary of tests that claim to find dozens or hundreds of sensitivities, or that sell supplements alongside the report.

Once You Know What to Avoid, Read the Label

Whether your clinician identifies a food allergy, an intolerance or celiac disease, the daily work is reading ingredient lists, because the problem ingredient can hide under other names. Foodsage is not a test and cannot tell you what you react to. After you and your clinician have decided what to avoid, you can add those ingredients to your profile, scan a product, and see which of its ingredients match. Foodsage provides ingredient information to help you shop. It does not diagnose or treat any condition.