METHODS FOR STUDY OF DIGESTIBILITY OF LIPIDS 201 



The feces are dried to constant weight in a vacuum oven at 80 °C, or in an 

 ordinary oven at 100 °C. The3 r are ground to a powder, from which ali- 

 quots are taken for the determination of fecal fat (see Section (6)). 



b. Determination of Metabolic Lipid. In order to calculate digestibil- 

 ity, it is necessary also, in the case of the rat, to make allowance for meta- 

 bolic lipid. One should realize that this correction may likewise be con- 

 sidered as a correction factor for metabolic lipid when applied to experi- 

 ments in which the digestibility of lipids other than fats is being tested. 

 To determine metabolic lipid, the same technic is applied, in the case of the 

 rat, as in the determination of the digestibility of fat (two-day orientation 

 period followed by eight- or nine-day experimental period), except that 

 the fat in the diet is completely replaced by sucrose. Since the interval 

 is relatively short and the rats are in a good state of nutrition so far as the 

 fat-soluble vitamins are concerned, the vitamin supplements are omitted 

 during the test period. 



Table 3 summarizes typical results which have been reported for meta- 

 bolic lipid in rats. 



Table 3 

 Metabolic Lipid as Determined by Experiments on Rats 



Investigator Augur Deuel Cheng Calbert 



et al. a etal.l>' c et al. c et al. d 



Number of rats 10 10 10 8 



Average weight of rats, g 209 ■ 170 166 215 



Average weight of dried stools, g 5 . 35 3 . 83 1 . 53 2 . 82 



Average neutral fat fraction in stools, 



mg 181 119 149 107 



Average soap fraction in stools, mg 87.5 122 72 81 



Total average feces fat, mg 268 241 221 188 



Metabolic lipid in feces, mg./g. dried 



feces 50.5 65.0 148.0 66.0 



a V. Augur, H. S. Rollman, and H. J. Deuel, Jr., J. Nutrition, 33, 177-186 (1947). 



6 H. J. Deuel, Jr., A. L. S. Cheng, and M. Ci. Morehouse, J. Nutrition, 35, 295-300 

 (1948). 



c A. L. S. Cheng, M. G. Morehouse, ami H. J. Deuel, Jr., J. Nutrition, 37, 237-250 

 (1949). (Fat-free diet in which Ca and Mg salts were omitted from the salt mixture.) 



d C. E. Calbert, S. M. Greenberg, G. Kryder, and H. J. Deuel, Jr., Food Research, 16, 

 294-305(1951). 



With the exception of the results of Cheng el al., h which were carried 

 out on rats fed a fat-free diet in which the calcium and magnesium salts 

 were omitted from the salt mixture, the results in the other three series of 

 tests are extremely constant, giving the average value for metabolic lipid 



8 A. L. S. Cheng, M. G. Morehouse, and H. J. Deuel, Jr., J. Nutrition, 37, 237-250 

 (1949). 



