Simple blood test for IBS-triggering foods shows promise in study

Michigan Medicine and Cleveland Clinic researchers have found that patients with irritable bowel syndrome were more likely to experience less abdominal pain if they followed a diet guided by the results of a blood test, compared to those who followed a sham elimination diet.

The blood test in this study (InFoods IBS, Biomerica) was specifically developed for patients with IBS and determined a positive test result for each food that triggered an above normal Immunoglobulin G antibody response, which is a marker of inflammation in patients with IBS. 

The study results were published in Gastroenterology.

Irritable bowel syndrome affects about 10% to 15% of adults in the United States.

Studies have shown that individuals who have IBS report a lower health-related quality of life and decreased work productivity.

Individuals with IBS experience various symptoms, including abdominal pain and cramps. Some factors, such as certain foods, can worsen symptoms and cause flare-ups.

“We have patients all the time who say, ‘I know food is a problem for me. Is there any way to figure out which foods I'm sensitive to?’” said Prashant Singh, MBBS, Michigan Medicine gastroenterologist and lead author on the paper.

This multicenter, randomized, double-blind, sham-controlled trial enrolled 238 study participants from eight academic centers in the United States.

Participants with IBS were screened with a validated, proprietary assay that tests IgG antibody levels to 18 different likely-culprit foods.

Patients were then assigned to one of two groups. One group eliminated the foods for which they tested positive on the IgG antibody assay.

The second group adhered to a rigorously designed sham diet.

People in the sham diet group eliminated foods similar to the ones for which they tested positive.

For instance, a patient who tested positive for a heightened IgG antibody response to walnuts would instead be asked to eliminate almonds (assuming they typically ate walnuts and almonds at a similar frequency.)

The results of the study found that 59.6% of participants who removed the foods detected on the test met an FDA-standard target for reduction in abdominal pain, compared to 42.2% of the patients in the control group who were on a sham diet.

Compared to the participants in the sham group, benefits of testing strategy were most pronounced in patients who have IBS with constipation (67.1% vs. 35.8%) or a mixture of constipation and diarrhea (66% vs. 29.5%).

“Patients had done all sorts of IgG antibody testing before, and it wasn’t very reliable. This latest test is supported by science. I can refer patients to this IBS-specific antibody testing, after explaining the science and the limitations of the study,” said Dr. Prashant Singh, MBBS.

While IgG antibody responses to food had previously been suggested as causing IBS symptoms, prior studies on IgG-based elimination diets had limitations, such as being single-center, IgG tests not adequately validated in patients with IBS, small sample size and lacking a well-designed sham diet for comparison.

“One of the main concerns with past research has been that some IgG response to food is normal,” Singh said.

“Generally, those studies have not given a rationale on how foods were selected and why they were selected. This study tried to overcome those limitations with an IBS-specific IgG-based test.”

The overall result of 59.6% of patients reaching the target for reduced abdominal pain (compared to 42.2% in the sham diet group) compares favorably to drugs evaluated using the same standard.

Compared to drugs, elimination diets offer the possibility of avoiding triggers of inflammation, rather than treating inflammation after it occurs.

However, existing elimination diets for patients with IBS – such as low FODMAP, which limits specific hard-to-digest carbohydrates – restrict a wide range of foods, making them potentially costly and hard to follow.

This IBS-specific, IgG-based diet has the advantage of allowing the patient to only eliminate a few specific trigger foods.

“Our diets are complex and identifying dietary triggers can be difficult.  This IBS-specific IgG test can help patients who suffer from IBS identify specific dietary triggers,” said Anthony Lembo, M.D., vice chair of Research at Cleveland Clinic’s Digestive Disease Institute, and a consultant for Biomerica.

The study’s positive results for participants with IBS-M (both diarrhea and constipation) are especially notable, as pharmaceutical interventions have historically helped people with either IBS-C (IBS with constipation) or IBS-D (IBS with diarrhea).

There are currently no FDA-approved drugs for patients with IBS-M.

William Chey, M.D., chief of Gastroenterology & Hepatology at the University of Michigan and an investigator in the study, said: “This IBS-specific, IgG antibody test requires additional validation but could move us one step closer to a ‘precision nutrition’ approach, in which providers can offer personalized dietary recommendations to each patient with IBS.”

Additional authors: Will Takakura, Brooks D. Cash, Brian E. Lacy, Eamonn M.M. Quigley, Charles W. Randall

Funding/disclosures: Biomerica Inc. funded the study.

Tech transfers/Conflicts of interest: Anthony Lembo and William D. Chey are consultants for Biomerica Inc.

Paper cited: “A novel, IBS-specific IgG ELISA-based elimination diet in irritable bowel syndrome: A randomized, sham-controlled trial,” Gastroenterology. DOI: 10.1053/j.gastro.2025.01.223