Is there a test for FODMAP intolerance?

No. There is no validated blood, breath or stool test that tells you which FODMAPs trigger your symptoms. The reliable way to find out is to cut FODMAPs back for a few weeks, then reintroduce them one group at a time and see how you feel.

IgG “food sensitivity” tests

These tests measure IgG antibodies to dozens of foods in a blood sample, often sold online or in clinics. A high IgG result mostly shows that you eat that food regularly. It is a normal response of the immune system, not a sign of intolerance.

The European Academy of Allergy and Clinical Immunology says IgG food tests should not be used to diagnose food allergy or intolerance.^[1] Cutting foods based on these results can mean giving up foods you tolerate, for no benefit.

Hydrogen breath tests

Breath tests measure gases made when bacteria ferment a sugar, such as lactose or fructose, that you drink in a test dose. They can show that a sugar is poorly absorbed, but poor absorption is common in people without symptoms too, and the test dose is larger than a normal serving.

For people with typical IBS symptoms, the British Society of Gastroenterology says breath tests have no role in diagnosing carbohydrate intolerance, including lactose intolerance.^[2] A breath test also covers only one sugar at a time, while FODMAPs come in six groups.

Tests your doctor may do

Before diagnosing IBS, doctors usually do a few targeted tests to rule out other conditions. A blood test for coeliac disease is the most common, and it matters because coeliac disease needs a strict gluten-free diet, not a low FODMAP one.^[2][3] Don’t cut out gluten before that test, or it can come back falsely negative.

What works instead: eliminate, then reintroduce

The low FODMAP diet works as its own test:

1. Cut back on all six FODMAP groups for 2 to 6 weeks.
2. If your symptoms improve, reintroduce one group at a time in rising amounts.
3. Keep everything you tolerate, and limit only what caused symptoms.

The low FODMAP diet guide explains each phase. A dietitian can tailor the plan to you.

Keeping track

The reintroduction phase only works if you can link what you ate to how you felt a few hours later. A paper diary works. Fodmi does the same on your iPhone: log meals by photo, voice or text, check in after eating, and see which foods line up with bad days. The food list shows how much of each food stays low FODMAP.