Digestibility of fatty acid monomers,dimers and polymers in the rat

This study was designed to determine digestibilities of fatty acid monomers, dimers and polymers as components of diets containing thermally oxidized oils. Male Wistar rats were fed semipurified diets supplemented with unheated, heated and a 1:1 mixture of unheated/heated olive oils at 6, 12 and 20% w/w of diet. In a 14-d experimental period, fecal lipids were extracted and analyzed by a combination of adsorption and high-performance size-exclusion chromatographies. Thus, it was possible to separate and quantitate five groups of fatty acids—nonpolar monomers, oxidized monomers, nonpolar dimers, oxidized dimers and polymers. Nonpolar fatty acid monomers showed high digestibilities, although significantly influenced by the alteration level of the dietary oil. The apparent absorption of oxidized fatty acid monomers averaged 76.6%. Among polymeric fatty acids, the lowest digestibilities were found for nonpolar dimers (10.9% on average), whereas oxidized dimers and polymers possessed higher apparent absorbability than expected, ranging from 22.7% to 49.6%. Chemical modifications prior to absorption, leading to less complex products, may have contributed to enhanced digestibility of polymers.