Hidden Food Allergies: A Cause of Irritable Bowel Syndrome

An estimated 30 to 45 million Americans suffer from irritable bowel syndrome (IBS). It has a major impact on quality of life and is responsible for frequent absenteeism from work and school. Those who have it know the symptoms all too well—frequent episodes of belly pain, often accompanied by diarrhea and/or constipation. Many undergo extensive medical testing, only to be told there’s nothing wrong. Adding to the frustration are the multiple medications available, some costing over $1000 per month, and all with limited effectiveness.

What role do foods play in IBS0? 50% of IBS sufferers feel that foods aggravate their symptoms but most are unable to pinpoint the specific culprits. The general consensus among IBS experts is that there is little or no connection between food allergies and IBS. As a result, food allergy testing generally is not recommended. Patients are often told just to watch what they eat or arbitrarily placed on the complicated low FODMAP avoidance diet, with limited success.

Based on two recent clinical studies,^1,2 a completely different type of food allergy is now being considered as playing a central role in triggering IBS symptoms in some individuals. These allergies are detected by a test procedure called patch testing, commonly used by dermatologists and allergists to identify causes of skin rashes resulting from substances found in skin care and other products that come in contact with the skin, thus the name “contact dermatitis.” Poison ivy is the most well-known example of contact dermatitis. Speaking technically, these allergies are caused by white blood cells called T lymphocytes.

In these studies, 122 individuals suffering from IBS were patch tested to up to 121 different foods. Following standard patch test protocols, investigators taped patches containing separate small wells for each specific food to the back (Figure) of each participant. After 2 days, the patches were taken off, and a final patch test reading was performed one or two days after that. Positive tests show up as small, usually itchy, red marks akin to a mild poison ivy-type reaction) where the specific food had been in contact with the skin. People with any positive tests were advised to avoid the foods that caused the positive tests for at least three months.  

Questionnaires to measure the effectiveness of the avoidance diets were completed by the study participants at several stages of the study. Using a 0 to 10 grading scale, 76% of those participants for whom there was long-term follow-up reported moderate to marked improvement in overall IBS symptoms, including nearly 51% reporting marked improvement (near or complete clearing of their symptoms).

Prior to these studies, investigators focused mostly on the widely recognized type of allergy responsible for peanut reactions and pollen allergies. Technically speaking, these allergies are caused by antibodies and histamine, a compound released by cells in this specific type of allergy. This type of allergy testing has proven to generally not be helpful in IBS; thus the consensus among experts that food “sensitivities” rather than true allergies are responsible in those 50% who report that foods aggravate their IBS symptoms. The recent patch test studies challenge this view and suggest the “sensitivities” often are true allergies—just not the type of allergy that had previously been considered. Of note, allergies can develop with repeated exposure at any point in time, not just to new exposures. For this reason, foods that once were not an issue can cause IBS symptoms at any point in a person’s life if an allergy to that particular food has developed.

The theory behind skin patch testing for IBS is that the skin and the intestinal lining are very similar. It is thought that an allergic reaction similar to that occurring in the skin from patch tests likely also occurs in the intestinal lining when the same foods are eaten. Avoidance of these foods prevents these allergic reactions, resulting in improvement or clearing of the IBS symptoms.

Importantly, a food allergy detectable by patch testing would not be detected by a prick and scratch or blood test, which are used to look for peanut-type allergies. Likewise, a peanut allergy would not be detected by a patch test. Ironically, all the previous efforts investigating peanut-type allergies in IBS were like barking up the wrong tree, looking for the wrong type of allergy.

Larger double-blinded, placebo- controlled studies are now being planned to confirm the game changing findings of these initial studies. In the meantime, in-office food patch testing called IBS-80 (www.IBS-80.com) is now available in select states throughout the United States.

About the author: Michael Stierstorfer, MD is a board-certified dermatologist and Clinical Associate Professor of Dermatology with the University of Pennsylvania. He maintains a private practice in North Wales, PA. Dr. Stierstorfer pioneered the utility of food patch testing for IBS after developing IBS symptoms himself in 2008. Determining that ingestion of foods containing garlic was the sole cause of his symptoms, he discovered that his newly developed allergy was detectable by patch testing, commonly used by dermatologists and allergists in evaluating causes of allergic contact dermatitis.

¹Shin GH, Smith MS, Toro B, Ehrlich AL, Luther S, Midani D, Hong I, Stierstorfer M. Utility of food patch testing in the evaluation and management of irritable bowel syndrome. Skin. 2018;2:1-15.

²Patch Test–Directed Dietary Avoidance in the Management of Irritable Bowel Syndrome. Cutis. 2021 August;108(02):91-95, E8-E9 | doi:10.12788/cutis.0321