Lactase and placebo in the management of the irritable bowel syndrome: a double-blind, cross-over study.

A double-blind, cross-over, therapeutic, clinical trial of the efficacy of exogenous, microbial beta-D-galactosidase to reduce the symptoms of the irritable bowel syndrome (IBS) was conducted in 12 patients whose customary diets regularly included milk. Eight of the 12 subjects (67%) proved to be lactase-nonpersistent, lactose-maldigesters when challenged with a aqueous dose of 12.5 g. The study lasted 4 months, with the first month a non-intervention, control period and the latter 3 months alternating in the sequence, treatment/placebo/treatment, or placebo/treatment/placebo. When symptoms during trial months were analyzed by the cumulative sum procedure, gastrointestinal symptoms were found to be independent of lactase treatment. We found a positive temporal association of the severity of both gastrointestinal and non-gastrointestinal symptomatology. In populations with a high prevalence of lactose deficiency, IBS symptoms appear to be independent of lactose maldigestion.