title: Review article: prebiotics in the gastrointestinal tract.
abstract: BACKGROUND
  Prebiotics are short-chain carbohydrates that alter the composition, or metabolism, of the gut microbiota in a beneficial manner. It is therefore expected that prebiotics will improve health in a way similar to probiotics, whilst at the same time being cheaper, and carrying less risk and being easier to incorporate into the diet than probiotics.
  
  
  OBJECTIVE
  To review published evidence for prebiotic effects on gut function and human health.
  
  
  METHODS
  We searched the Science Citation Index with the terms prebiotic, microbiota, gut bacteria, large intestine, mucosa, bowel habit, constipation, diarrhoea, inflammatory bowel disease, Crohn's disease, ulcerative colitis, pouchitis, calcium and cancer, focussing principally on studies in humans and reports in the English language. Search of the Cochrane Library did not identify any clinical study or meta-analysis on this topic.
  
  
  RESULTS
  Three prebiotics, oligofructose, galacto-oligosaccharides and lactulose, clearly alter the balance of the large bowel microbiota by increasing bifidobacteria and Lactobacillus numbers. These carbohydrates are fermented and give rise to short-chain fatty acid and intestinal gas; however, effects on bowel habit are relatively small. Randomized-controlled trials of their effect in a clinical context are few, although animal studies show anti-inflammatory effects in inflammatory bowel disease, while calcium absorption is increased.
  
  
  CONCLUSIONS
  It is still early days for prebiotics, but they offer the potential to modify the gut microbial balance in such a way as to bring direct health benefits cheaply and safely.
authors.affiliation: Dundee University Gut Group, Division of Pathology and Neuroscience, Ninewells Hospital and Medical School, Dundee, UK. s.macfarlane@dundee.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Macfarlane
authors.forename: G T
authors.initials: GT
authors.lastname: Macfarlane
authors.forename: J H
authors.initials: JH
authors.lastname: Cummings
mesh_terms: D001842:Bone and Bones / Q000378:metabolism; D002118:Calcium / Q000493:pharmacokinetics; D003248:Constipation / Q000378:metabolism; D003967:Diarrhea / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D019587:Dietary Supplements; D005285:Fermentation / Q000502:physiology; D005765:Gastrointestinal Agents / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000378:metabolism / Q000382:microbiology*; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism / Q000382:microbiology; D043183:Irritable Bowel Syndrome / Q000378:metabolism; D007792:Lactulose / Q000008:administration & dosage; D009844:Oligosaccharides / Q000008:administration & dosage / Q000378:metabolism
chemical_list: D004040:Dietary Carbohydrates; D005765:Gastrointestinal Agents; D009844:Oligosaccharides; C120489:oligofructose; D007792:Lactulose; D002118:Calcium