Lactose is the main source of calories in milk, an essential nutriedigestion, patients with visceral hypersensitivity nt in infancy and a key part of the diet in populations that maintain the ability to digest this disaccharide in adulthood. Lactase deficiency (LD) is the failure to express the enzyme that hydrolyses lactose into galactose and glucose in the small intestine. The genetic mechanism of lactase persistence in adult Caucasians is mediated by a single C→T nucleotide polymorphism at the LCTbo −13’910 locus on chromosome-2. Lactose malabsorption (LM) refers to any cause of failure to digest and/or absorb lactose in the small intestine. This includes primary genetic and also secondary LD due to infection or other conditions that affect the mucosal integrity of the small bowel. Lactose intolerance (LI) is defined as the onset of abdominal symptoms such as abdominal pain, bloating and diarrhoea after lactose ingestion by an individual with LM. The likelihood of LI depends on the lactose dose, lactase expression and the intestinal microbiome. Independent of lactose digestion, patients with visceral hypersensitivity associated with anxiety or the Irritable Bowel Syndrome (IBS) are at increased risk of the condition. Diagnostic investigations available to diagnose LM and LI include genetic, endoscopic and physiological tests. The association between self-reported LI, objective findings and clinical outcome of dietary intervention is variable. Treatment of LI can include low-lactose diet, lactase supplementation and, potentially, colonic adaptation by prebiotics. The clinical outcome of these treatments is modest, because lactose is just one of a number of poorly absorbed carbohydrates which can cause symptoms by similar mechanisms.
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Contributors MB and BM performed the literature search, collated the information and produced the first draft of the manuscript. KV and MRF contributed additional material and edited the publication. All authors discussed and revised the draft and approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests MF has received research funding from Nestlé International for studies of lactose digestion and tolerance.
Provenance and peer review Commissioned; externally peer reviewed.
Collaborators Professor Ning Dai, Department of Gastroenterology, Zhejiang University School of Medicine, Sir Run Run Shaw Hospital, Hangzhou, Zhejiang, China, 310016; E-mail: firstname.lastname@example.org. Dr Lars Fadnes, Department of Global Public Health and Primary Care, University of Bergen and Bergen Addiction Research Group, Department of Addiction Medicine, Haukeland University Hospital, Post box 7804, 5020 Bergen, Norway (Web: http://www.uib.no/en/persons/Lars.Thore.Fadnes) E-mail: Lars.Fadnes@uib.no
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