title: Of the milk sugars, galactose, but not prebiotic galacto-oligosaccharide, improves insulin sensitivity in male Sprague-Dawley rats.
abstract: BACKGROUND
  Consumption of dairy products reduces risk of type 2 diabetes. Milk proteins and fats exhibit anti-diabetic properties but milk sugars have been studied little in this context. Galactose from milk lactose is readily converted to glycogen in the liver but its effects on insulin sensitivity have not been assessed. Prebiotic oligosaccharides from milk alter gut microbiota and can thereby influence host metabolism. Our objective was to assess the effect on insulin sensitivity of dietary galactose compared to glucose and fructose, and fermentable galacto-oligosaccharides compared to non-fermentable methylcellulose.
  
  
  METHODS
  Diets containing 15% of dry matter from glucose, fructose, galactose, galacto-oligosaccharides, or methylcellulose were fed to 36 rats per diet for 9 weeks. Hyperinsulinemic-euglycemic clamps with [3-3H]glucose infusion and a steady-state 2-[1-14C]deoxyglucose bolus injection were used to assess insulin sensitivity and glucose uptake indices. Tissue was collected in fed, fasted and fasted, insulin-stimulated states.
  
  
  RESULTS
  Galactose increased glucose infusion rate during the clamp by 53% and decreased endogenous glucose production by 57% compared to glucose and fructose. Fed-state hepatic glycogen content was greater with galactose compared to glucose and fructose, consistent with a potentiation of the insulin effect on glycogen synthase by dephosphorylation. Galactose decreased the fecal Firmicutes:Bacteroidetes ratio while galacto-oligosaccharides increased abundance of fecal Bifidobacterium spp. 481-fold compared to methylcellulose, and also increased abundance of Lactobacillus spp. and Bacteroidetes. Galacto-oligosaccharides did not affect glucose infusion rate or endogenous glucose production during basal or clamp periods compared to methylcellulose.
  
  
  CONCLUSIONS
  Galactose at 15% of daily intake improved hepatic insulin sensitivity in rats compared to glucose and fructose. Galactose caused an increase in fed-state hepatic glycogen content and a favourable shift in gut microbial populations. Intake of galacto-oligosaccharides improved the gut microbial profile but did not improve insulin sensitivity.
authors.affiliation: Department of Animal Biosciences, University of Guelph, Guelph, Canada.
authors.forename: Priska
authors.identifier: http://orcid.org/0000-0001-7759-0916
authors.initials: P
authors.lastname: Stahel
authors.affiliation: Department of Animal Biosciences, University of Guelph, Guelph, Canada.
authors.forename: Julie J
authors.initials: JJ
authors.lastname: Kim
authors.affiliation: Departments of Medicine and Physiology, University of Toronto, Toronto, Canada.
authors.forename: Changting
authors.initials: C
authors.lastname: Xiao
authors.affiliation: Department of Animal Biosciences, University of Guelph, Guelph, Canada.
authors.forename: John P
authors.initials: JP
authors.lastname: Cant
mesh_terms: D000818:Animals; D001644:Bifidobacterium / Q000187:drug effects; D005632:Fructose / Q000378:metabolism; D005690:Galactose / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D007333:Insulin Resistance; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000382:microbiology; D008297:Male; D008892:Milk / Q000737:chemistry*; D009844:Oligosaccharides / Q000737:chemistry / Q000494:pharmacology*; D056692:Prebiotics / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D009844:Oligosaccharides; D056692:Prebiotics; D005632:Fructose; D005947:Glucose; D005690:Galactose