906 XIV. NUTRITIONAL VALUE OF FATS 



in a number of human subjects, allowing for the excretion of fecal soaps. 

 The coefficients of digestibility obtained in these latter experiments are 

 identical with the ones reported by the U. S. Dept. of Agriculture. This 

 result was obtained in spite of the increased fat accounted for as soaps, 

 because of a corresponding increase in the quantity of "metabolic fat" 

 when soaps were included in the latter correction. It is our opinion that the 

 failure to consider the fecal soaps in the case of experiments on vegetable 

 fats or on low-melting animal fats probablj^ does not alter their digestibility 

 figures. ^Moreover, the diet was extremely constant in the large number of 

 experiments carried on at the U. S. Dept. of Agriculture, which would 

 probably not in^'olve much ^'ariation in the proportion of calcium contained 

 in the diet. However, in the case of the fats containing largely stearic acid, 

 the figures recorded for digestibility in these earlier studies are probably too 

 high. Obviously, further studies in this field are necessary. For a further 

 discussion of the effect of calcium and magnesium on fat digestibility see 

 page 877. 



(b) Resume of the Comparative Digestibility of Fats and Oils. In the case 

 of man there are no marked variations in the high utilization of most com- 

 mon natural fats. Thus, the same high coefficients of digestibility have 

 been noted in vegetable fats and in animal fats melting below 50°C. More- 

 over, h^^drogenated fats, such as shortenings and margarines, present the 

 same high values for utilization as is the case with natural fats, provided 

 that the melting points of these fats are below 50°C. Both butter and a 

 margarine prepared from a hydrogenated vegetable fat had coefficients of 

 digestibifity of 97%. 



Animal fats melting above the critical level of 50°C. (122°F.) are pro- 

 gressively less efficiently utilized by man and by animals as the melting 

 points are further increased. However, this situation is not confined to 

 the animal fats, as it likewise occurs in the case of vegetable fats which 

 have been hj^drogenated to melting points exceeding this critical tempera- 

 ture. Thus, from the standpoint of digestibifity, animal fats, butters, 

 vegetable fats, and hydrogenated oils are almost equal, provided that the 

 samples considered do not ha^•e excessivel}^ high melting points. The 

 various factors which alter the digestibifity of fat may also affect the sev- 

 eral types of fat in a similar manner. 



c. The Effect of Absorption on the Nutritional Value of Fats. Nutri- 

 tionists do not always differentiate between absorption and digestibility of 

 foodstuffs. However, these biologic determinations actually constitute 

 two separate indices for evaluating the nutritional value of a fat, and varia- 

 tions in absoiption rate may, under some conditions, be of considerable 



