False Perceptions of Lactose Intolerance in Patients with Irritable Bowel Syndrome

Researchers in China report that although lactose intolerance (LI) may be more prevalent in patients with irritable bowel syndrome (IBS), patients’ frequently erroneously self-diagnose as lactose intolerant due to their heightened attention to gastrointestinal symptoms (such as nausea, abdominal pain, bloating, and diarrhea) that overlap between the two conditions.

Consequently, IBS patients are “hypervigilant to diet-related symptoms and display marked avoidance behavior to various foods, including dairy products,” and often “attribute digestive problems to LI but have no evidence of this condition on objective investigation.” This can lead patients to avoid dairy products unnecessarily, “with potential adverse effects on nutritional health.”

In “Prevalence and Presentation of Lactose Intolerance and Effects on Dairy Product Intake in Healthy Subjects and Patients with Irritable Bowel Syndrome,” published in Clinical Gastroenterology and Hepatology, the authors noted that a recent consensus development statement from the US National Institutes of Health “recognized LI as a common and important cause of functional gastrointestinal symptoms.” The statement also recognized that there is “a lack of knowledge about epidemiology, diagnosis, and management strategies” for LI.

To further investigate the relationship between these conditions and the impact LI can have on IBS patients’ dietary habits, the researchers used a lactose hydrogen breath test (HBT) to asses lactose absorption and tolerance and the intake of dairy products in 60 healthy controls and 60 patients who met Rome III criteria for diarrhea-predominant IBS (D-IBS).

In this double-blind, randomized, controlled three-way crossover trial, participants were given 10, 20, and 40 g lactose tablets on three different days, each separated by 7—14 days. Patients recorded breath samples at 15-minute intervals over the course of three hours following lactose ingestion. Researchers also recorded the number and severity of gastrointestinal symptoms over 24 hours following testing. Patients also provided details about their intake of dairy and other lactose-containing products for the three months prior to the study.

Analysis of study data revealed the following results:

• The prevalence of lactose malabsorption (LM) and LI increased with lactose dose
• There was no difference in LM prevalence at any dose, with a “diagnostic rise in breath hydrogen for 93% of controls and 92% of D-IBS subjects at the 40-g lactose dose”
• Only three participants had “objective and subjective findings consistent with lactase persistence”
• The prevalence of LI was lower for controls than for D-IBS subjects at 10 g and 40 g lactose
• There were “no significant differences in LI symptom rate and severity between LM-negative and LM-positive IBS patients except at the 10-g lactose dose”
• D-IBS patients reported less frequent intake of dairy products than controls, but a similar amount of lactose in their diet
• More D-IBS patients than controls self-reported LI (63% vs 22%)

In their discussion of these results, the authors reported that “the prevalence of LI was significantly higher in D-IBS patients than in controls. Especially at low and intermediate doses of lactose, the presence of functional gastrointestinal disease increased the likelihood that an individual would report abdominal pain, bloating, and diarrhea.” They wrote that this finding was “consistent with the hypothesis that D-IBS patients are more sensitive and/or more likely to report symptoms (hypervigilant) than healthy controls in response to “events” in the gastrointestinal tract.” Because of this tendency, many IBS patients “completely avoid dairy products, an approach that may adversely impact on nutritional health and that rarely provides adequate relief of symptoms.”

This is noteworthy because previous studies have found that patients with IBS tend to display a high degree of “anxiety and hypervigilance for symptoms related to dairy intake,” which limits the diagnostic value (and usefulness in directing therapy) of self-reported lactose intolerance in IBS patients. This “underline[s] the difficulty that patients have in identifying dietary triggers for their functional gastrointestinal symptoms and the need for objective testing.”

In conclusion, the authors wrote that this study “shows that the likelihood of developing abdominal symptoms after lactose ingestion was related to the dose of lactose, expression of lactase in the intestine, action of colonic flora, and the presence of functional gastrointestinal disease. Patient intake of milk products was associated more closely with patient perception of lactose tolerance than objective evidence on HBT.”