Lactose intolerance and probiotics: from pathophysiological mechanisms to clinical applications

Lactose is a disaccharide found in dairy products, which provide energy and essential nutrients. Digestion of lactose relies on the intestinal enzyme lactase, or lactase-phlorizin hydrolase, located on the brush border of the small bowel mucosa. This enzyme splits lactose into two absorbable monosaccharides: glucose and galactose. When lactase activity is insufficient, undigested lactose proceeds to the colon where it is fermented by the gut flora, generating gas that trigger the uncomfortable symptoms associated with lactose intolerance. Lactase non-persistence is extremely common, affecting approximately 70% of the adult population world-wide. Prevalence varies markedly across geographic regions, typically ranging from 50 to 90% in African, Asian, and South American countries. The subjective diagnosis of lactose intolerance requires the occurrence of symptoms such as abdominal pain, bloating, flatulence and diarrhea following the ingestion of high lactose dairy products. An objective assessment of lactose intolerance may be achieved with a specific breath test that measures hydrogen emission in breath following the ingestion of lactose. Consequently, current international guidelines require concurrent report of typical symptoms and pathologic breath test results in order to diagnose lactose intolerance. Management of lactose intolerance often involves dietary restrictions and the prescription of formulations that contain lactase. However, one should recognize that avoiding dairy products can increase the risk of nutritional deficiencies. Therefore, ongoing research is focused on alternative strategies, notably utilizing gut microbiota in order to improve tolerance to lactose. This review aims to explore the evidence supporting the use of probiotics as a potential treatment strategy to alleviate the symptoms of lactose intolerance by modulating colonic metabolism and enhancing lactose digestion.