Short chain fatty acids in inflammatory bowel disease. The effect of bacterial fermentation of blood.

An in vitro faecal incubation system was used to investigate how blood added to faeces influences short chain fatty acid (SCFA) production. The result was a change in SCFA pattern from one largely dominated by acetate and propionate to a pattern less dominated by these two acids but with greater amounts of longer and branched SCFA (butyrate, isobutyrate, valerate and isovalerate). Patients with active ulcerative colitis revealed variable concentrations of SCFA in their individual stool specimens, 66% of the samples being outside the 95% confidence interval set by a control group and without any specific trend. The SCFA concentrations were normal in patients with Crohn's disease of the colon. The study concludes that the changes in SCFA pattern seen elsewhere in studies on ulcerative colitis could be due to bacterial fermentation of blood either in the colon or in the stools after passing. It cautions against using faecal concentrations in this disease without due regard to the phenomenon of dilution or pollution of the colonic chymus by colonic effusion of blood.