Impact of Positive Glucose, Lactose, and Fructose Hydrogen Breath Tests on Symptoms and Quality of Life in Irritable Bowel Syndrome.

Background: Gas production due to fermentation from fructose malabsorption (FM) or lactose malabsorption (LM) and small intestinal bacterial overgrowth (SIBO) contribute to the development of gastrointestinal symptoms in patients with irritable bowel syndrome (IBS). However, the impact of the carbohydrate malabsorption, unlike SIBO, is relatively unknown.

Methodology: A multicenter, prospective study of consecutive adults with IBS who underwent a hydrogen breath test (HBT) (glucose, 75 g; lactose, 25 g; or fructose, 25 g) was conducted. The proportion of patients who tested positive for glucose, fructose and lactose HBT were evaluated. The symptom severity, psychology, and quality of life of subjects with SIBO were compared with those having LM and/or FM. Independent factors associated with severe IBS (IBS-symptom severity scale: IBS-SSS > 300) were explored.

Results: A total of 116 subjects were included (median age 56 years, male 35.3%). Of these, 23.3% (27/116), 85.7% (24/28), and 44.4% (16/36) of them tested positive for glucose, lactose, and fructose HBT, respectively. Among those with a positive HBT (n = 65), patients with SIBO were more likely to have the diarrhea-predominant subtype of IBS (77.8% vs. 47.4%, p = 0.014). Severe IBS was associated with SIBO, compared with LM/FM (SIBO: 36.4% vs. LM: 9.1%/FM 13.3%, p = 0.016). With multivariate analysis, SIBO (OR 5.25, p = 0.028) and depression (OR 5.59, p = 0.030) were independently associated with severe IBS.

Conclusion: Although LM and FM commonly co-exist in IBS, their clinical relevance appears to be less significant than that of SIBO. The connection between SIBO with depression reinforces the importance of the microbiome-gut-brain axis in IBS.