Short-chain fatty acids and bowel functions in man.

The fecal excretion of short-chain fatty acids (SCFAs) (measured by gas chromatography), transit time (assayed by radiopaque plastic markers), fecal weight, intake of dietary fiber, and their relationship have been studied in 10 healthy subjects during 1 week. The subjects had a fiber intake (mean +/- SD) of 26.3 +/- 7.9 g/day, a fecal weight of 160 +/- 49 g/day, and an average transit time of 41 +/- 9 h and excreted 11.1 +/- 5.5 mmol of SCFAs/day, with a concentration of 66.7 +/- 28.0 mmol/kg feces. The mean amount of SCFAs, but not their concentration, correlated to mean fecal weight (p less than 0.01) and mean transit time (p less than 0.01). The mean fecal weight correlated to mean transit time (p less than 0.05). The mean intake of dietary fiber did not correlate to any of the other variables. The results of this study indicate that other substrates are more important than fiber for the bacterial formation of SCFAs in the colon. The SCFAs formed most likely do not exert any direct laxative effect.