A Study of the Absorption of Fat and Carotene from the Gastro-intestinal Tract *

The lipolytic hypothesis of fat absorption advocated by Verzar and McDougall7 in 1936 maintains: that ingested fat undergoes emulsification to soap and complete hydrolysis to fatty acid and glycerol in the small intestine; that a solid pavement epithelial structure exists on the intestinal mucosal cells; that the fatty acids pass through the membrane as soluble complexes with bile salts, while glycerides do not pass through the membrane; that all fatty acid is resynthesized to tri-glyceride in the intestinal cell, in which process phosphorylation under control of the adrenal gland is essential; that paraffins may not be absorbed; and that the particles of fat pass into the blood stream via the lacteal-lymphatic system. Frazer in 19383 brought forward the partition hypothesis of fat absorption as an alternative hypothesis and maintains:4 that emulsification occurs through the formation of a triple complex of "fatty acid/bile salt/lower glyceride"; that only partial hydrolysis is possible to fatty acid and diand monoglycerides and later glycerol; that a cannicular structure is present on the outer intestinal mucosal layers; that fatty acids pass through the membrane either as soluble compounds or complexes, while glycerides pass through the membrane as a finely dispersed emulsion of negatively charged particles less than 0.5 in diameter; that the adrenal cortex controls the normal electrolyte balance which is closely related to the absorption of charged particles; that resynthesis is not essential in the absorptive mechanism; and that the fatty acid fraction passes to the liver mainly via the portal system, whereas the glyceride fraction passes via the lacteal-lymphatic system to the blood stream and thence to the fat depots. In addition to demonstrating that glycerides may be absorbed, Frazer5 has shown that paraffin emulsions may also be absorbed. In light of this and in order to elucidate further the mechanism of the absorption of carotene, the following experiment was designed. A relationship between carotene and fat absorption is known in that fat enhances the absorption of carotene.1