The clinical relevance of lactose malabsorption in irritable bowel syndrome.

Objective : The prevalence of lactose malabsorption (LM) in the Caucasian population of northern Europe is estimated to be low. Irritable bowel syndrome (IBS) is a very common diagnosis, and its symptoms are nearly identical to those of LM. Therefore we investigated the prevalence of LM among IBS patients in comparison with healthy volunteers. Design : A double-blind clinical trial compared with healthy controls. Setting : One out-patient gastroenterology clinic in the Netherlands. Patients : 70 Caucasian IBS patients and 35 healthy volunteers (staff members). Methods : All 105 underwent hydrogen (H 2 ) breath and blood glucose tests, after an oral intake of 50 grams of lactose. The IBS patients were treated with a lactose-restricted diet for 6 weeks. They completed a lactose intake score before, and a symptom score scored by six separate criteria, before, during and after treatment. Results : In 17 out of 70 (24.3%) IBS patients LM was detected, in comparison with 2 out of 35 (5.7%) controls (P<0.009). There was no difference in the pre-entry mean lactose intake and symptom score between the LM positive and negative IBS patients. The mean symptom score of the LM positive group showed a marked decrease after 6 weeks of dietary therapy (P<0.001). Conclusion : A substantial number of IBS patients showed a clinically unrecognized lactose malabsorption, which could not be discriminated by symptoms and dietary history, and which can be treated with a lactose-restricted diet. Therefore LM has to be excluded before the diagnosis IBS is made.