Food: The Forgotten Factor in the Irritable Bowel Syndrome

After years of inattention, there is a growing body of evidence to suggest that dietary constituents at least exacerbate symptoms and perhaps contribute to the pathogenesis of the irritable bowel syndrome (IBS). Although patients with IBS self-report food allergies more often than the general population, the evidence suggests that true food allergies are relatively uncommon. Less clearly defined food intolerances may be an important contributor to symptoms in IBS patients. This article reviews the literature supporting a causal link between food and the symptoms of IBS as well as the evidence supporting dietary interventions as a means of managing IBS symptoms.

Between 7% and 20% of adults experience symptoms compatible with the irritable bowel syndrome (IBS), a disorder defined by the presence of recurring episodes of abdominal pain in association with altered bowel habits and no evidence of a structural or easily identifiable biochemical abnormality that might explain these symptoms. Several factors have been suggested as playing a role in the pathogenesis of IBS, including disturbed motility, the brain-gut axis, genetic factors, impaired gut barrier function, immunologic dysregulation, the gut microbiome, and psychosocial factors. More recently, there has been increasing attention on the role of food in IBS. Patients have long associated their IBS symptoms with the ingestion of certain foods, combinations of foods, or a meal itself. More than 60% of IBS patients report worsening of symptoms after meals, 28% of these within 15 minutes after eating and 93% within 3 hours. Unfortunately, the lack of empiric data proving a causal link or consistently documenting symptom improvement has caused health care providers to view dietary interventions with skepticism. Furthermore, even to this day, gastroenterologists and primary care providers receive virtually no structured training in dietary interventions for IBS. This lack of enthusiasm for dietary counseling has increasingly caused providers to be misaligned with their patients who are increasingly seeking more holistic solutions for their IBS symptoms. Out of desperation, many providers recommend or passively stand by as their patients empirically attempt various dietary manipulations, such as the elimination of fatty foods, fruits, gluten, or milk/dairy products or modifying dietary fiber content. This haphazard approach not surprisingly leads to inconsistent results, which can be frustrating to both patients and providers.

Several disorders and diseases can masquerade as or exacerbate the symptoms of IBS. For example, few clinicians would dispute that celiac disease and lactose intolerance are important considerations in patients presenting with IBS symptoms. These two well-defined disorders likely represent the tip of the iceberg, however, pertaining to the role of food in IBS. This article reviews the literature supporting a causal link between food and the symptoms of IBS as well as the evidence supporting dietary intervention as a means of treating IBS.

The scope of the problem

Adverse reactions to food are acknowledged by 5% to 45% of the general population, and GI complaints are predominant in approximately one-third to one-half of those affected. Offending foods are often referred to as trigger foods, dietary triggers, or culprit foods, sometimes leading to a nutritionally inadequate diet. Although food intolerance is a common perception among the general population, it can be demonstrated in only a relatively small proportion of the population when double-blind food elimination and challenge studies are employed. In a population study of food intolerance of 20,000 patients, 20.4% complained of food intolerance. Of the 93 subjects who entered the double-blind, placebo-controlled food challenge, 11.4%-27.4% had a positive reaction, with estimated prevalence of reactions to the 8 foods tested varying from 1.4% to 1.8% depending on the method of testing used. Women perceived food intolerance more frequently and showed a higher rate of positive results to food challenge.

Among individuals with IBS, 20% to 67% complain of subjective food intolerance, which is more prevalent than similar reports in matched controls. One population-based study reported a prevalence rate of perceived food intolerance of greater than 50% among subjects with IBS, a rate that was 2-fold greater than that reported by those without IBS. Another found that patients in a GI clinic with a final diagnosis of a functional disorder were four times more likely to report food allergies (FAs) or adverse reaction to food. The likelihood of a patient’s symptoms being functional increased even further if adverse reactions to both drugs and foods were reported. Such complaints seem to correlate with female gender and anxiety level in those with functional GI disorders.

Many patients suffering from IBS report an association of symptoms with specific foods. Although the foods that induce symptoms may be specific, the associated symptoms are often nonspecific and consistent with functional disorders, such as IBS. Many patients identify specific trigger foods (most commonly dairy, fructose, wheat products, and caffeine), but there is little evidence that IBS patients with food-related complaints are suffering from a true FA. Although there are undoubtedly some patients with IBS symptoms who suffer from an FA, the proportion of the total population of IBS sufferers with a true FA is small. Alternatively, there is likely to be substantial overlap between food intolerances/sensitivities and IBS, because these syndromes often have similar clinical presentations.

It is not uncommon for IBS patients to experiment with their diet or limit their diet before seeking medical attention. The foodstuffs most commonly implicated are wheat, corn, dairy products, coffee, tea, and citrus fruits. In a 2005 population-based sample comparing dietary consumption of specific food items and nutrients between individuals with IBS or dyspeptic symptoms and those without symptoms, no differences were seen in the consumption of frequently suspected culprit foods. In a survey of more than 1200 individuals with IBS, 63% were interested in knowing which foods to avoid. The lifestyle changes they had made or considered for treatment of IBS included small meals (69%); avoiding fatty foods (64%); higher fiber intake (58%); and avoiding milk products (54%), carbohydrates (43%), caffeine (41%), alcohol (27%), and high-protein foods, such as meats (21%).

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