134 II. DIGESTION AND ABSORPTION OF FATS 



shown to take place within twenty-four hours, subjects with "idiopathic" 

 hyperlipemia and the nephrotic syndrome were found to utilize the labeled 

 lipid more slowly. Kirchmair 631 employed a similar method for the deter- 

 mination of lipid absorption in rabbits, based upon the rate of excretion 

 of ordinary iodine in the urine. A method for preparing iodized fat is 

 described by Rutenburg et al. 632 



g. Elaeostearic Acid as a Tracer for the Study of Fat Absorption. Fil- 

 lerup and Mead 633 have proposed that small amounts of /3-elaeostearic 

 acid (prepared from tung oil) be incorporated in the fat under investigation. 

 The amount of total fat absorbed can be calculated spectrophotometrically 

 from the rate of disappearance of the conjugated acid. The rate of ab- 

 sorption, in mice, of methyl oleate (mixed with 5% methyl-/3-elaeostearate) 

 was shown to be identical when calculated by the standard Cori technic, 

 or by the use of the elaeostearate tracer. However, the incorporation of 

 the elaeostearate into the fat increased the rate of absorption. The pro- 

 cedure has likewise been used in a human subject for the indirect deter- 

 mination of fat absorption by following the levels of elaeostearate in the 

 blood. 634 



6. The Digestion of Fats 



The main changes involved in the digestion of foodstuffs in the gastro- 

 intestinal tract are due to hydrolysis. In the case of proteins and carbo- 

 hydrates, these hydrolytic changes are so extensive that the end-products 

 have only a fraction of the molecular weight of the original components in 

 the food. These hydrolyses not only bring about a greater solubility of the 

 products, but they also permit wider flexibility in the substances which can 

 be synthesized from these building blocks. It is, of course, obvious that 

 the simpler the unit, the more diverse are the products which can be syn- 

 thesized from it. 



The scope of the hydrolyses which take place in the digestion of fat is 

 extremely minor compared with that in the digestion of proteins and carbo- 

 hydrates. At most, only three linkages are capable of hydrolysis in the 

 triglyceride molecule, and there is some dispute as to whether all of these 

 possible points of splitting are actually attacked before absorption occurs. 



63i H. Kirchmair, Klin. Wochschr., 27, 588-589 (1949). 



832 A. M. Rutenburg, A. M. Seligman, and J. Fine, J. Clin. Invest., 28, 1105-1109 

 (1949). 



633 D. L. Fillerup and J. F. Mead, Absorption and Distribution Sttidies Using Eleostearic 

 Acid, UCLA-148, Atomic Energy Project, Aug. 7, 1951. 



634 J. F. Mead, D. L. Fillerup, A. B. Decker, and L. R. Bennett, J. Nutrition, 46, 499- 

 513 (1952). 



