title: Evidence for greater production of colonic short-chain fatty acids in overweight than lean humans.
abstract: BACKGROUND
  Short-chain fatty acids (SCFA) are produced by colonic microbiota from dietary carbohydrates and proteins that reach the colon. It has been suggested that SCFA may promote obesity via increased colonic energy availability. Recent studies suggest obese humans have higher faecal SCFA than lean, but it is unclear whether this difference is due to increased SCFA production or reduced absorption.
  
  
  OBJECTIVE
  To compare rectal SCFA absorption, dietary intake and faecal microbial profile in lean (LN) versus overweight and obese (OWO) individuals.
  
  
  METHODS
  Eleven LN and eleven OWO individuals completed a 3-day diet record, provided a fresh faecal sample and had SCFA absorption measured using the rectal dialysis bag method. The procedures were repeated after 2 weeks.
  
  
  RESULTS
  Age-adjusted faecal SCFA concentration was significantly higher in OWO than LN individuals (81.3±7.4 vs 64.1±10.4 mmol kg(-1), P=0.023). SCFA absorption (24.4±0.8% vs 24.7±1.2%, respectively, P=0.787) and dietary intakes were similar between the groups, except for a higher fat intake in OWO individuals. However, fat intake did not correlate with SCFAs or bacterial abundance. OWO individuals had higher relative Firmicutes abundance (83.1±4.1 vs 69.5±5.8%, respectively, P=0.008) and a higher Firmicutes:Bacteriodetes ratio (P=0.023) than LN individuals. There was a positive correlation between Firmicutes and faecal SCFA within the whole group (r=0.507, P=0.044), with a stronger correlation after adjusting for available carbohydrate (r=0.615, P=0.005).
  
  
  CONCLUSIONS
  The higher faecal SCFA in OWO individuals is not because of differences in SCFA absorption or diet. Our results are consistent with the hypothesis that OWO individuals produce more colonic SCFA than LN individuals because of differences in colonic microbiota. However, further studies are needed to prove this.
authors.affiliation: Faculty of Medicine, Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Rahat-Rozenbloom
authors.affiliation: Faculty of Medicine, Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Fernandes
authors.affiliation: Department of Biochemistry, The University of Western Ontario, London, Ontario, Canada.
authors.forename: G B
authors.initials: GB
authors.lastname: Gloor
authors.affiliation: 1] Faculty of Medicine, Department of Nutritional Sciences, University of Toronto, Toronto, Ontario, Canada [2] Clinical Nutrition and Risk Factor Modification Centre, and Division of Endocrinology and Metabolism and Li Ka Shing Knowledge Institute, St Michael's Hospital Toronto, Toronto, Ontario, Canada.
authors.forename: T M S
authors.initials: TM
authors.lastname: Wolever
mesh_terms: D000328:Adult; D003106:Colon / Q000378:metabolism* / Q000382:microbiology; D004032:Diet; D015930:Diet Records; D004040:Dietary Carbohydrates / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism; D005232:Fatty Acids, Volatile / Q000378:metabolism*; D005243:Feces / Q000382:microbiology*; D005260:Female; D006801:Humans; D008297:Male; D050177:Overweight / Q000378:metabolism* / Q000382:microbiology; D010865:Pilot Projects; D065590:Rectal Absorption; D013851:Thinness / Q000378:metabolism* / Q000382:microbiology
chemical_list: D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005232:Fatty Acids, Volatile