Comparative study of endogenous fecal fatty acids in germ-free and conventional rats

The effects of gastrointestinal flora on the quantitative and qualitative aspects of "endogenous" fecal fatty acid excretion were studied in the rat using germ-free (GF) and conventional (CVL) animals, lipid-free diet and open-tubular gas-liquid chromatography. Gastrointestinal flora slightly increased endogenous excretion of fatty acids. Analysis of fatty acids from different fecal lipid fractions showed that the presence of a microflora in the gastrointestinal tract extensively modified the qualitative aspects of endogenous fecal fatty acid spectra. In total endogenous fecal lipids, concentrations of mono and polyunsaturated fatty acids (from C16 to C22) were 3.5 times higher in GF rats, while concentrations of even-numbered and saturated fatty acids were 1.5 times higher in CVL rats. Odd-numbered fatty acids (from C11:10 to C2:0) represented 6.5% of total endogenous fecal fatty acids in CVL rats vensus 1.5% in GF rats. Branched-chain fatty acid (even-and-odd-numbered, iso and anteiso) concentrations were 12.9% in CVL rats versus 2.0% in GF rats. Results clearly showed that the gastrointestinal flora was the main source of odd-numbered fatty acids and branched-chain fatty acids in endogenous fecal lipids. However, a secondary source may also exist since these fatty acids represented 3.5% of the total endogenous fatty acids in GF rats.