title: Differential impact of lactose/lactase phenotype on colonic microflora.
abstract: BACKGROUND
  The ability to digest lactose divides the world's population into two phenotypes that may be risk variability markers for several diseases. Prebiotic effects likely favour lactose maldigesters who experience lactose spilling into their colon.
  
  
  OBJECTIVE
  To evaluate the effects of fixed-dose lactose solutions on fecal bifidobacteria and lactobacilli in digesters and maldigesters, and to determine whether the concept of a difference in ability to digest lactose is supported.
  
  
  METHODS
  A four-week study was performed in 23 lactose maldigesters and 18 digesters. Following two weeks of dairy food withdrawal, subjects ingested 25 g of lactose twice a day for two weeks. Stool bifidobacteria and lactobacilli counts pre- and postintervention were measured as the primary outcome. For secondary outcomes, total anaerobes, Enterobacteriaceae, beta-galactosidase and N-acetyl-beta-D-glucosaminidase activity in stool, as well as breath hydrogen and symptoms following lactose challenge tests, were measured.
  
  
  RESULTS
  Lactose maldigesters had a mean change difference (0.72 log10 colony forming unitsg stool; P=0.04) in bifidobacteria counts compared with lactose digesters. Lactobacilli counts were increased, but not significantly. Nevertheless, reduced breath hydrogen after lactose ingestion correlated with lactobacilli (r=-0.5; P<0.001). Reduced total breath hydrogen and symptom scorestogether, with a rise in fecal enzymes after intervention, were appropriate, but not significant.
  
  
  CONCLUSIONS
  Despite failure to achieve full colonic adaptation, the present study provided evidence for a differential impact of lactose on microflora depending on genetic lactase status. A prebiotic effect was evident in lactose maldigesters but not in lactose digesters. This may play a role in modifying the mechanisms of certain disease risks related to dairy food consumption between the two phenotypes.
authors.affiliation: Division of Gastroenterology, Department of Medicine, McGill School of Medicine, Montreal, Quebec. aszilagy@gas.jgh.mcgill.ca
authors.forename: Andrew
authors.initials: A
authors.lastname: Szilagyi
authors.forename: Ian
authors.initials: I
authors.lastname: Shrier
authors.forename: Debra
authors.initials: D
authors.lastname: Heilpern
authors.forename: Jung
authors.initials: J
authors.lastname: Je
authors.forename: Sunghoon
authors.initials: S
authors.lastname: Park
authors.forename: George
authors.initials: G
authors.lastname: Chong
authors.forename: Catherine
authors.initials: C
authors.lastname: Lalonde
authors.forename: Louis-Francois
authors.initials: LF
authors.lastname: Cote
authors.forename: Byong
authors.initials: B
authors.lastname: Lee
mesh_terms: D000328:Adult; D001644:Bifidobacterium / Q000254:growth & development; D001944:Breath Tests; D003106:Colon / Q000382:microbiology*; D015169:Colony Count, Microbial; D005243:Feces / Q000201:enzymology; D005260:Female; D006801:Humans; D043322:Lactase / Q000235:genetics*; D007778:Lactobacillus / Q000254:growth & development; D007785:Lactose / Q000235:genetics* / Q000378:metabolism; D007787:Lactose Intolerance / Q000175:diagnosis* / Q000628:therapy; D008297:Male; D010641:Phenotype; D010865:Pilot Projects; D055815:Young Adult; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D043322:Lactase; D001616:beta-Galactosidase; D007785:Lactose