This randomized study evaluates the usefulness of the I31 probiotic formula, against placebo, in the treatment of symptoms of lactose intolerance.

People with lactose intolerance are unable to fully digest the sugar (lactose) in milk. As a result, they may have diarrhea, abdominal pain, gas and bloating after eating or drinking dairy products. A deficiency of lactase - an enzyme produced in your small intestine - is usually responsible for lactose intolerance. Many people have low levels of lactase but are able to digest milk products without problems. In lactose intolerance, though, lactase deficiency leads to symptoms after eating dairy foods.

I31 is a probiotic formula composed of Pediococcus acidilactici strain CECT7483 and Lactobacillus plantarum strains CECT7484 and CECT7485, previously shown to improve intestinal sensitivity in patients with Irritable Bowel Syndrome (IBS). IBS is a functional intestinal disease in which recurrent abdominal pain is associated with defecation or a change in bowel habits, often accompanied by bloating. Given the overlap in symptoms between IBS and lactose intolerance, it is hypothesized that I31 formula could be beneficial for individuals with lactose intolerance.

Inclusion Criteria:

• Subjects attending Hospital Juarez de Mexico with self-reported lactose intolerance, a minimum lactose intolerance symptom score of 6 points, 20ppm during the Lactose Hydrogen Breath Test (LHBT) and providing Informed Consent.

Exclusion Criteria:

• More than 10 ppm before ingestion of lactose in the Lactose Hydrogen Breath Test (LHBT). If such value was observed, the LHBT test was repeated on a 2nd day, and if >10ppm persisted, patient was excluded.
• BMI below 18 or above 40
• Subjects not accepting to maintain their dietary and physical activity pattern unchanged for the duration of the study
• Subjects with congenital lactase deficiency
• Pregnant or lactating women
• Significant gastrointestinal disease, such as inflammatory bowel disease, coeliac disease, chronic diarrhea or gastroparesis
• History of gastrointestinal surgery in the 6 months prior to inclusion
• History of intestinal perforation
• History of acute gastroenteritis, acute gastroenteritis or hospitalization in the 4 weeks prior to inclusion
• Substance abuse
• Untreated thyroid disorder
• Cancer
• Other severe diseases that in the doctor's opinion could interfere with the study
• Known allergy to any of the components in the treatments