Food Intolerance and Irritable Bowel Syndrome: Sorting Out the Overlap

A presentation on October 14, 2013, by Sheila Crow, MD, FRCPC, FACP, FACG, AGAF, (University of California San Diego) at the American College of Gastroenterologists Annual Scientific Session

Crowe SE. Food intolerances and IBS: coexistent or separate entities?

Sheila Crowe, MD, may be a specialist, but she often faces one of the most common primary care complaints: nonspecific abdominal and bowel complaints that are ascribed to irritable bowel syndrome (IBS). Intractable IBS is a common cause for gastroenterologist referral-often primary care physicians are stymied by the absence of a systematic approach to these patients and the lack of an easily treated diagnosis. The patients often arrive with preconceived notions of what foods may be causing their symptoms-diet faddism and food marketing are feeding these beliefs. Dr Crowe approaches these patients very, very systematically, and her approach is instructive for anyone who sees patients with these complaints. She acknowledges that sometimes what the patient is eating is making him or her sick. 

Food allergies, celiac disease (CD), and food sensitivities are on the rise in the US, and any of them can be confused with IBS, defined by the Rome III criteriaas abdominal pain or discomfort for at least 3 days per month in the past 3 months, associated with at least 2 of the following:
• Improvement with defecation
• Onset associated with a change in stool frequency
• Onset associated with change in appearance of the stool

IBS may in fact be associated with certain foods. A recent European study of 193 adults revealed that 19% met Rome III criteria and that those patients ate more canned food, processed meat, legumes, whole cereals, sweets, and fruit compotes. Are these people reacting to highly processed foods and a high-carbohydrate (gas-forming) diet? In a Swedish study of 197 IBS patients, 84% reported symptoms associated with one or more foods; 70% reported problems with carbohydrates (dairy, legumes, apple, flour, plums). Dr Crowe’s review shows there is minimal (but not zero) evidence for the benefit of dietary treatments for IBS and other functional GI disorders. This includes low fat, carbohydrate restriction, FODMAP restriction, the so-called paleo diet, candida restriction, and others.

It’s a different story with CD: a significant fraction of IBS-labeled patients may actually have CD or the emerging non-celiac gluten sensitivitydiagnosis. As such, the ACG recommends testing for CD in patients with IBS-D (diarrhea-predominant) because there may be as much as a 4-fold increased prevalence of CD in IBS populations. For many celiac-negative patients, future research may eventually conclude that other components in wheat-not gluten-are causing symptoms. In a randomized controlled trial of a gluten-free diet in IBS-D, a gluten-free diet was shown to improve stool frequency and gut permeability, especially in those who were HLA DQ2/8–positive.

In a review of the evidence for a link between food allergies and IBS, the result is inconclusive for the role of food allergy. Most patients with food intolerances in IBS have nonspecific reactions through presumed neurohormonal mechanisms rather than IgE-mediated processes. Food allergies are real entities, but their presentation is usually closely associated in time with intake-delay is minimal. Remember that food allergy may present as typical soft tissue swelling, urticaria/eczema, or respiratory symptoms (or even anaphylaxis), but it can also present with nausea, vomiting, diarrhea, abdominal pain or bloating-all resulting from intestinal angioedema. Again, the distinction will be the clear and quick temporal association with specific typical allergenic foods. The top 8 food allergens in North America are cow’s milk, eggs, peanuts, wheat (this is not CD), corn, tree nuts, and fish and other seafood. Systematic study of elimination diets in IBS patients randomized to specific elimination diet versus sham elimination diet showed mixed results. Most of these patients have food intolerance with nonspecific reactions to food. While allergy causes serious problems, though, it’s probably not the culprit in IBS.

Finally, some IBS patients are experiencing physiological food reactions that are normal responses to foods or food quantity-and some individuals will perceive this as pathological. Careful history taking can help you determine whether IBS complaints are being fueled by:
• Overeating, with distention and esophageal regurgitation
• Excessive fatty foods, with delayed gastric emptying and altered motility
• Excessive legumes, cruciferous vegetables, garlic, or onions, with excessive flatulence
• Excessive non-absorbable or poorly absorbed sugars and carbohydrates with diarrhea, bloating, and flatulence
• Lactose intolerance

So-by all means, reassure your patients that while IBS, allergies, and celiac aren’t normal, flatulence is. Tell them that Dr Crowe, from the University of California San Diego quoted a figure of 14 such “experiences” daily as being typical. But first, make sure you’re not missing anything treatable or serious in these patients.