New IgG Food Sensitivity Test Shows Promise in Managing Irritable Bowel Syndrome

Elimination diets guided by a novel immunoglobulin G (IgG) food sensitivity test can reduce abdominal pain and improve symptoms in patients with irritable bowel syndrome (IBS), according to a study co-authored by a leading Houston Methodist Hospital gastroenterologist.

Results from the randomized, controlled trial, published in the journal Gastroenterology, recently resulted in FDA approval for the new diagnostic assay, providing clinicians with a promising new tool to help manage a condition that affects up to 9% of the global population.

"Many IBS patients believe their symptoms are related to food, but until now we haven't had a validated test to guide those decisions," said Dr. Eamonn Quigley, study co-author and chief of Gastroenterology at Houston Methodist. "This is the first large, well-controlled study to show that an IgG-based approach can make a significant difference, particularly for patients with constipation and mixed typology."

Trial design

The study enrolled 238 patients across eight U.S. centers, including Houston Methodist Hospital. Participants were screened using the Biomerica inFoods® IBS ELISA, a test designed specifically for patients with irritable bowel syndrome to identify IgG responses to 18 common foods. Participants were then assigned either to eliminate foods flagged by the test or to follow a sham elimination diet.

Results showed that 59.6% of patients on the IgG-guided diet achieved at least a 30% reduction in abdominal pain intensity for two or more of the last four weeks of the study period, compared with 42.1% in the sham group (P = .02). The benefit was most pronounced in patients with constipation-predominant IBS and mixed-type IBS, the latter subgroup of which lacks effective therapeutic interventions.

"We have medications for people with constipation-predominant IBS and medications for people with diarrhea-predominant IBS, but, importantly, we have no medications available for people with mixed-type IBS," Dr. Quigley explained. "That's one of the most exciting things about this study, the fact that patients with this type may finally find some relief."

A long-standing question

The study offers long-awaited evidence to support dietary interventions based on immune response.

"Unlike the classic IgE-mediated food allergies, which can trigger life-threatening reactions such as anaphylaxis, IgG-mediated responses reflect prolonged immune activity and may point to foods that exacerbate irritable bowel symptoms in certain individuals," Dr. Quigley said.

Houston Methodist is now among the first centers in the U.S. to offer the inFoods IBS test to patients. The process involves a simple at-home finger-stick blood collection. Results are sent to both the patient and physician, who can then generate a tailored elimination diet plan.

"I think it's important to say upfront that we don't necessarily think this is a cure for all IBS, and it won't help everyone," Dr. Quigley said. "But for the right patients, in combination with lifestyle changes and other available therapies, it can make a significant impact on quality of life."

Next steps

The most frequently implicated foods in the trial were eggs, cow's milk and wheat. Dr. Quigley noted that outcomes typically began to improve within two weeks of elimination and persisted throughout the eight-week trial.

While the study was one of the largest of its kind, Dr. Quigley cautioned that more research is needed.

"But the arrival of a commercially available, FDA-cleared test is an important development," Dr. Quigley said. "It moves us closer to personalized dietary therapy, rather than the trial-and-error approaches patients with irritable bowel syndrome have had to rely on for decades."