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 dietand open-tubular gas-liquid chromatography. Gastroin- testinal 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 C 16 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 C 11:0 to C2 1:0) represented 6.5% of total endogenous fecal fatty acids in CVL rats versus 1.5% in GF rats. Branched-chain fattyacid (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 fattyacidsin GF rats. Am. J. Clin. Nutr. 32: 2027-2032, 1979.