High Prevalence of Small Intestinal Bacterial Overgrowth in Lactose Intolerance Patients: Is It a Chicken and Egg Situation?

Background: Lactose intolerance is highly prevalent in Mediterranean area. Substantial portions of patients remain symptomatic in spite of fair lactose-free diet.
Aims: Assess in a series of IBS consecutive patients: 1) the prevalence of lactose intolerance; 2) the frequency of association of lactose intolerance with SIBO; 3) the possibility of SIBO as a cause of symptom persistence in patients with lactose intolerance on lactose-free diet; 4) the ability of LHBT to diagnose SIBO.
Place and Duration of the Study: Patients were recruited from November 2011 to July 2012 at the Gastroenterology Unit of Mauriziano Hospital U.Ist , Turin, Italy.
Methodology: Lactose malabsorption was assessed by means of LHBT and SIBO by means of GHBT and LHBT, using Breath Tracker digital microlyzer on 500 IBS patients and 50 controls. SIBO was treated, with rifaximin 1200 mg a day for 2 weeks, randomly, on 1 to 1 basis.
Results: Prevalence of lactose intolerance resulted to be 59% in IBS patients and 6% in controls, with a statistically significant difference (p<.001). SIBO was present in 72% of patients with lactose intolerance in IBS group, ad in none of the subjects with lactose malabsorption (3) in control group. After 6 months, 105 out of 106 patients affected by LI + SIBO treated with rifaximin + lactose free diet, and 34 out of 107 patients affected by LI + SIBO treated only with a lactose free diet resulted completely asymptomatic. Concordance between LHBT and GHBT for SIBO diagnosis was 98%.
Conclusions: Lactose intolerance is a common condition in patients with IBS in Northwest Italy (59%) very frequently associated with SIBO (72%). This association turned out to be a major cause of symptom persistence in patients on lactose-free diet until successful eradication of SIBO was achieved. LHBT is a simple test able to diagnose simultaneously lactose malabsorption and SIBO.