Lactose intolerance in patients with chronic functional diarrhoea: the role of small intestinal bacterial overgrowth

BACKGROUND: Many studies report a high prevalence of lactose intolerance in patients with functional, gastrointestinal disease. AIM: To evaluate the role of small intestinal bacterial overgrowth (SIBO) in condition of lactose intolerance and the mechanism by which SIBO may impact lactose tolerance in affected patients. METHODS: Consecutive out-patients with chronic functional diarrhoea (CFD) and healthy controls underwent a validated 20 g lactose hydrogen breath test (HBT). Patients completed also a 10 g lactulose HBT with concurrent assessment of small bowel transit by scintigraphy. RESULTS: Lactose malabsorption was present in 27/31 (87%) patients with CFD and 29/32 (91%) healthy controls (P = 0.708). From the patient group 14/27 (52%) had lactose intolerance and 13/27 (48%) experienced no symptoms (lactose malabsorption controls). Only 5 (17%) healthy controls reported symptoms (P < 0.01). The oro-caecal transit time was similar between patient groups with or without symptoms (P = 0.969). SIBO was present in 11 (41%) subjects and was more prevalent in lactose intolerance than in lactose malabsorption [9/14 (64%) vs. 2/13 (15%), P = 0.018]. Symptom severity was similar in lactose intolerance patients with and without SIBO (P = 0.344). CONCLUSIONS: Small intestinal bacterial overgrowth increases the likelihood of lactose intolerance in patients with CFD as a direct result of lactose fermentation in the small intestine, independent of oro-caecal transit time and visceral sensitivity.