Can a food sensitivity test identify IBS triggers?

You have probably seen the ad. Prick your finger, send in your blood, and get a color-coded list of the foods supposedly "triggering" everything that is wrong with you. Whenever patients ask about food sensitivity tests, my answer has always been the same: the science does not support these tests.

The idea of food-sensitivity testing is reasonable on its surface: your gut's immune system produces antibodies against specific foods. By identifying which foods your gut's immune system is responding to, you could build a targeted elimination diet to help with symptoms. The problem is these tests rely on immunoglobulin G (or IgG) production against a certain food. Making IgG against a food is considered normal, unlike other immunoglobulins such as IgE, which the body produces when someone is allergic to a food. For example, IgE drives the body's anaphylaxis reaction against peanuts. IgG production, however, often means nothing more than that you eat the food regularly and can be a marker of tolerance, not harm. That is precisely why allergy and gastroenterology societies have advised against the use of mail-in consumer "food sensitivity" panels, distinct from food allergy testing, which relies on IgE production.

But a recent trial may change the medical community's perspective regarding food sensitivity panels - at least for IBS patients. Published in Gastroenterology, researchers conducted a randomized, double-blind, sham-controlled trial and found that an IgG-guided elimination diet improved IBS symptoms compared to a sham (placebo) diet.

The test in this trial, inFoods IBS, was not a generic or existing panel with a new label. It was built specifically for IBS. Instead of flagging every food a patient produces IgG against, it uses IBS-specific cutoffs (from comparing people with IBS to people without) to surface only the foods where the response runs meaningfully above normal. In practice, the test flagged just two to four foods per person, most commonly eggs, cow's milk, and wheat. Compare this to the direct-to-consumer kits available online, which flag 20 or more foods.

To strengthen the validity of the test, the researchers compared the treatment diet to a sham placebo diet. Two hundred and thirty-eight people with IBS were enrolled and split into two groups. The treatment group eliminated the foods their food sensitivity test flagged. The control group also eliminated foods, but foods their test did not flag (for example, tested positive for walnuts? You were told to eliminate almonds instead). Both groups believed they were on a personalized elimination diet, so the trial tested whether the IgG guidance made a difference, not just the effect of being told you were on a personalized diet based on your blood test. The control group measuring the placebo effect is exactly what most food-sensitivity "studies" leave out.

Over eight weeks, the treatment group experienced a greater reduction in symptoms than the sham diet group. Approximately 60% of patients met the target of a 30% drop in abdominal pain, versus 42% on the sham diet, which was a statistically significant difference. One thing to note is the noticeable improvement in symptoms in the sham diet group. More than four in ten people improved by eliminating random foods, which quantifies the sizeable placebo response. Therefore, the response to the elimination diet test is a combination of the meaningful effect of the treatment diet plus a notable placebo response. The benefit of sensitivity testing to develop a treatment diet was strongest in constipation-predominant (IBS-C) and mixed (IBS-M) IBS, and weakest in the diarrhea-predominant (IBS-D) group.

Two things to note. First, the study was funded by the company that sells the test. This does not invalidate the study results - it was well designed and peer-reviewed in a highly reputable gastroenterology journal - but it is important to contextualize the findings. Second, the inFoods IBS test is not currently FDA-approved, but it is orderable directly through the company. Further studies in a wider patient population are needed, and the authors themselves call for a larger study.

What does this mean if you have IBS? If food drives your symptoms but you struggle to identify your triggers, this specific test may be worth discussing with your healthcare team, especially if you have IBS-C or IBS-M. It is important to note that this test is just one of many possible treatment approaches for IBS, and the results of this study do not support the use of the other food-sensitivity tests showing up on your social media feed.