The fecal excretion of phospholipids was determined in three adult males during the last 4 days of three 8- to 16-day periods on a fat-free diet. The phospholipids were isolated and identified by column and thin-layer chromatography on silicic acid. The individual phospholipids were quantitatively estimated by gas chromatographic determination of the component fatty acids, using methyl heptadecanoate as internal standard. The range of total excretion of phospholipids was 64–100 mg/day per 100 g of dry feces. In all samples the major phospholipids were tentatively identified as phosphatidyl ethanolamine, phosphatidyl glycerol, and phosphatidyl inositol. Phosphatidyl ethanolamine made up 31–41% of the total excretion. All the phospholipids contained about the same fatty acids (C14–C27), but in somewhat varying proportions. Because of the occurrence of large amounts of the odd carbon number, among both branched and long chain fatty acids, which are not commonly associated with mammalian metabolism, the presence of phospholipids in the feces was attributed to bacterial synthesis.
