Short-chain fatty acids in the normal human feces

The short-chain fatty acids ( SCFAs ) have been studied in the feces of 20 healthy subjects--10 methane excretors and 10 non-methane excretors. The analytical procedure included homogenization of fecal samples followed by vacuum distillation and subsequent gas chromatography. This method for analysis of fecal SCFAs showed recoveries of the individual acids from 90% to 109% and coefficients of variation for the inter-assay reproducibility from 6.0% to 19.7%, highest for those acids present in the smallest concentrations. There was no difference in the concentrations or relative compositions of SCFAs between methane-excreting subjects and non-methane-excreting subjects. The concentrations of SCFAs , given as mmol/kg feces (wet weight), were (median and range): total, 76.8 (27.9-187.7); acetic acid, 37.4 (12.8-103.4); propionic acid, 12.5 (4.5-27.8); i-butyric acid, 2.2 (0.7-3.8); n-butyric acid, 12.4 (4.0-53.0); i-valeric acid, 3.2 (0.8-5.9); n-valeric acid, 2.4 (0.6-3.8) and n-caproic acid, 0.5 (0.0-3.6). The study shows that the SCFAs are quantitatively the most important anions in the feces of healthy subjects. The pronounced individual variations in the concentrations of SCFAs are real biological variations and cannot be explained by methodological variations.