Inability of the human fecal microflora to metabolize the nonabsorbable fat substitute, olestra

Olestra is a non-caloric fat substitute under review by the Food and Drug Administration. It consists of a mixture of octa-, hepta- and hexaesters of sucrose formed with long chain fatty acids. Previous studies showed olestra is not hydrolyzed by mammalian lipases and is not absorbed. The objective of this study was to evaluate the potential for colonic microflora to metabolize olestra after continued exposure. Neat and emulsified14C-[fatty acid] olestra was incubated for 72 h in both minimal and organically-enriched anaerobic media inoculated with feces from seven subjects who had consumed olestra (9 g per day) over a 3–4 week period.14C-sucrose and14C-glucose served as positive controls. Production of14CO2,14CH4,14C-volatile fatty acids (VFAs) and14C-long chain fatty acids (LCFAs) was determined. In addition, the ester distribution and fatty acid composition of olestra were examined before and after incubation. Significant quantities of14CO2 and14C-VFAs were generated from the14C-sugars, indicating that the microflora were active under the incubation conditions. Furthermore, free oleic acid was extensively hydroxylated and hydrogenated. In contrast, no degradation products (gas, VFAs, LCFAs) or changes in the olestra resulting from bacterial activity were detected. These results indicate that under anaerobic conditions the colonic microflora of the humans, consuming olestra, did not metabolize olestra.