title: Fecal acetate is inversely related to acetate absorption from the human rectum and distal colon.
abstract: In humans, colonic bacteria ferment unabsorbed carbohydrates, producing the SCFA acetic, propionic and n-butyric acids. To test for interactions among the SCFA that may affect their absorption, healthy subjects (n = 10) were given 300-mL rectal infusions containing acetate (60 mmol/L), propionate (20 mmol/L) and butyrate (20 mmol/L), alone or in combinations of two or three. The solutions were retained for 30 min, and then subjects voided a sample for SCFA measurement. To examine the relationship between absorption and fecal SCFA concentrations, a fecal sample was collected at the end of the study. The mean percentage of butyrate absorption (30.2 +/- 4.6%) exceeded that of acetate (24.1 +/- 3.7%) (P < 0.05). Absorption tended to be less (P = 0.12) when a SCFA was infused alone (26.7 +/- 4.0%) than when all three were infused (32.0 +/- 5.7%). Bicarbonate concentration was higher after butyrate-containing infusions than after saline. The fecal molar acetate percentage was inversely correlated with the percentage of acetate absorption from the infusion of three SCFA (r = -0.834, P < 0.005). We conclude that there was no combination effect on SCFA absorption, and the chain-length effect suggests passive diffusion as a likely mechanism of absorption. Furthermore, fecal acetate may reflect absorption, rather than production of colonic acetate.
authors.affiliation: Department of Nutritional Sciences, University of Toronto, Toronto, Canada.
authors.forename: Janet A
authors.initials: JA
authors.lastname: Vogt
authors.forename: Thomas M S
authors.initials: TM
authors.lastname: Wolever
mesh_terms: D019342:Acetic Acid / Q000008:administration & dosage / Q000032:analysis* / Q000493:pharmacokinetics*; D000328:Adult; D001639:Bicarbonates / Q000032:analysis; D001944:Breath Tests; D020148:Butyric Acid / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics; D003106:Colon / Q000378:metabolism*; D005243:Feces / Q000737:chemistry*; D005260:Female; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D008697:Methane / Q000032:analysis; D011422:Propionates / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics; D012007:Rectum / Q000378:metabolism*; D012996:Solutions
chemical_list: D001639:Bicarbonates; D011422:Propionates; D012996:Solutions; D020148:Butyric Acid; C029658:propionic acid; D008697:Methane; D019342:Acetic Acid