title: Low serum levels of short-chain fatty acids after lactulose ingestion may indicate impaired colonic fermentation in patients with irritable bowel syndrome.
abstract: BACKGROUND
  Ingestion of low-digestible carbohydrates triggers symptoms in patients with irritable bowel syndrome (IBS). These carbohydrates become substrates for microbial fermentation in the colon, yielding short-chain fatty acids (SCFAs) that are readily absorbed. Aiming to compare colonic fermentation in patients with IBS and healthy controls, we analyzed the concentrations of SCFA in serum at fasting and 90 minutes following ingestion of an unabsorbable, but fermentable carbohydrate, lactulose.
  
  
  METHODS
  Patients with IBS according to Rome III criteria (n=22) and healthy controls (n=20) ingested 10 g lactulose dissolved in water. Symptoms were graded by questionnaires and SCFA were analyzed using hollow fiber-supported liquid membrane extraction coupled with gas chromatography.
  
  
  RESULTS
  Lactulose induced more symptoms in patients with IBS than in healthy controls (P=0.0001). Fasting serum levels of SCFA did not differ between patients with IBS and controls. However, the postprandial levels of total SCFA (P=0.0002), acetic acid (P=0.005), propionic acid (P=0.0001), and butyric acid (P=0.01) were significantly lower in patients with IBS compared with healthy controls. There was no correlation between the levels of serum SCFA and symptom severity.
  
  
  CONCLUSIONS
  Low-serum levels of SCFA after lactulose ingestion may indicate impaired colonic fermentation in patients with IBS. Conceivably, this disturbance is related to symptom generation, but the mechanism is not clear.
authors.affiliation: Department of Radiology, Lovisenberg Diaconal Hospital, Oslo, Norway.
authors.forename: Ragnhild
authors.initials: R
authors.lastname: Undseth
authors.affiliation: Food for Health Science Centre, Lund University, Lund, Sweden.
authors.forename: Greta
authors.initials: G
authors.lastname: Jakobsdottir
authors.affiliation: Food for Health Science Centre, Lund University, Lund, Sweden.
authors.forename: Margareta
authors.initials: M
authors.lastname: Nyman
authors.affiliation: Unger-Vetlesen Institute, Lovisenberg Diaconal Hospital, Oslo, Norway.
authors.forename: Arnold
authors.initials: A
authors.lastname: Berstad
authors.affiliation: Unger-Vetlesen Institute, Lovisenberg Diaconal Hospital, Oslo, Norway.
authors.forename: Jørgen
authors.initials: J
authors.lastname: Valeur
keywords: FODMAP; fermentation; irritable bowel syndrome; microbiota; short-chain fatty acids