At-Home Food Sensitivity Tests: What the IgG Number Measures

When bloating, cramps or loose stools keep coming back, a mail-order kit that tests a finger-prick of blood against dozens or hundreds of foods can look like a shortcut. The report usually sorts foods into colored bands and suggests which to cut. Before you order one, or start removing foods from a report you already have, here is what the main number measures.

What IgG shows

IgG is a type of antibody. Many food sensitivity kits measure IgG, or its subtype IgG4, against each food on the panel.

Allergy¹ specialists read that number differently from the kits. The Canadian Society of Allergy and Clinical Immunology says food-specific IgG is a marker of exposure and tolerance to food.¹ The American Academy of Allergy², Asthma & Immunology (AAAAI) calls it likely a normal immune response to eating the food.² Lab medicine specialists say the same: it reflects previous exposure, not hypersensitivity.³

That’s why a report often flags the foods you eat most, such as eggs, dairy, wheat or the almonds in your morning yogurt. Your body has met them often.

What the professional groups say

• The Canadian society “strongly discourages” food-specific IgG testing for identifying or predicting reactions to food.¹
• The AAAAI says the test has never been scientifically proven to do what it reports to do.²
• The Association for Diagnostics & Laboratory Medicine³ advises clinicians: “Do not order IgG food allergen testing.” It notes that American, European and Canadian allergy organizations all recommend against it.³
• The NHS⁴ says some food intolerance tests sold to the public are not recommended. It notes limited evidence for their accuracy and warns that cutting out several foods can be harmful.⁴

The risks of acting on the list

Cutting foods you don’t need to cut. The Canadian position warns that misuse of the test leads to unnecessary dietary restrictions and a lower quality of life.¹ Dropping dairy, for example, removes a main calcium source at an age when bone health matters.

Muddying a celiac test. If wheat is on your list and you go gluten-free first, a later celiac test may not be accurate. NIDDK says doctors don’t recommend starting a gluten-free diet before diagnostic testing, because it can affect the results.⁵ Ask for celiac testing before you cut gluten.

Missing an allergy. The test isn’t designed to find true food allergies. The Canadian society warns that a person with a dangerous IgE-mediated allergy could be advised to put that food back in their diet.¹ If a food causes hives, swelling, throat tightness or trouble breathing, see a clinician about allergy testing instead.

What to do instead

1. Keep a food and symptom diary for a few weeks. The NHS⁴ describes this as a way to work out what may be triggering symptoms.⁴ Note what you ate and when, plus bloating, pain, bowel habits, stress, sleep and where you are in your cycle if you still have one.
2. Take the diary to a visit. The NHS⁴ advises against cutting foods out without the advice of a doctor or dietitian, and to see a doctor if food intolerance symptoms keep coming back.⁴ For a suspected allergy, an allergist uses your history, skin prick tests, IgE blood tests and, when needed, a supervised food challenge.³
3. Ask about a guided elimination. If a food pattern shows up, a registered dietitian can help you test one change at a time and bring foods back in a planned way.

Try: “My bloating comes back most days. Here’s my diary. Which tests make sense for me, and should I see a dietitian before I cut anything out?”

Don’t let a kit delay these checks

NIDDK lists symptoms that may point to something other than irritable bowel syndrome: anemia, rectal bleeding, bloody or black, tarry stools, and weight loss. Your doctor will also ask about family history of conditions such as celiac disease, colon cancer and inflammatory bowel disease.⁶ If any of these apply, book a visit rather than a test kit.

Bloated by Dinner includes a Belly Clock log and a Test-It list with a visit script. Use them to track your symptoms against meals and to bring organized questions to the appointment. See the book.