Kate Johnson

November 11, 2015

SAN ANTONIO — Food allergy and atopy might be underlying factors in some patients with irritable bowel syndrome (IBS), two new studies suggest.

In fact, the constellation of allergic asthma, rhinitis, and eczema in a subgroup of IBS patients goes hand-in-hand with diarrhea and gastrointestinal reactions to food.

"The thinking is that if you can figure out their food allergies, you can really improve their diarrhea and abdominal pain. And we see in the clinic that they do feel better," said senior investigator Mary Tobin, MD, an allergist at the Rush University Medical Center in Chicago.

The findings of both studies were presented here at the American College of Allergy, Asthma & Immunology 2015 Annual Scientific Meeting.

In a previous study that Dr Tobin was involved in, patients with atopic symptoms were shown to be more likely to have IBS than patients without atopic symptoms (odds ratio, 3.2) (Ann Allergy Asthma Immunol. 2008;100:49-53).

In their current study, Dr Tobin and her colleagues identified a possible connection between the allergic airway and the allergic gut.

They evaluated 122 with atopic IBS and 32 with nonatopic IBS. Median age was 34.2 years.

In patients with atopic IBS, the predominant GI symptom was diarrhea, whereas in those with nonatopic IBS, the predominant GI symptom was constipation (P < .05).

The diarrhea is possibly from increased mucosal mast cells and gut permeability, which are associated with IgE-mediated reactions, such as food allergy, Dr Tobin explained.

Testing for Food Allergies

In the second study, 48 patients with atopic IBS, 65% of whom reported GI symptoms after eating specific foods, underwent skin prick testing for a panel of food allergens, including peanut, tree nuts, fish, shellfish, egg, milk, cereals, meats, poultry, fruits, vegetables, and legumes. Mean age was 37.2 years.

The skin prick test indicated sensitization to the suspected trigger food in 60% of the patients.

For those with a positive skin prick test, 17% also had responses to the trigger food suggestive of an IgE-mediated reaction, such as hives, angioedema, abrupt nausea and vomiting, and asthma.

These findings indicate that food allergen sensitization has a significant role in the pathogenesis of atopic IBS, said Dr Tobin, who was also involved in this study.

 
A positive, or negative, skin prick does not mean allergy, or exclude it, especially in patients with gastroenterological symptoms.
 

However, there are "several points of weakness" in this research, said Antonio Carroccio, MD, Ospedale Civili Riuniti in Sciacca, Italy.

The association between atopy and IBS is "well known and real," and there is "a probable role of food antigens in the pathogenesis of the IBS-like symptoms," he told Medscape Medical News.

But the study is limited to skin prick assays. "A positive, or negative, skin prick does not mean allergy, or exclude it, especially in patients with gastroenterological symptoms," he pointed out.

Dr Carroccio, who was involved in a recent review of food allergy and IBS (World J Gastroenterol. 2015;21:7089-7109), said he tends to agree that "food allergy could be a possible cause of irritable bowel syndrome, and a dietary approach should be implemented in clinical practice." However, he pointed out, the work by Dr Tobin's team and others "has yet to prove this."

"Food challenge remains the unique gold standard for the diagnosis of food allergy in patients with GI symptoms. Consequently, their conclusion that the majority of their subjects suffer from food allergy is not correct," he explained.

"The authors can affirm that the majority of subjects have a positive skin prick test for one or more foods, but no direct relation can be proved between the foods and the IBS."

Dr Tobin and Dr Carroccio have disclosed no relevant financial relationships.

American College of Allergy, Asthma & Immunology (ACAAI) 2015 Annual Scientific Meeting: Abstract 243, presented November 7, 2015; Abstract 15, presented November 8, 2015.

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