FACTORS ALTERING NUTRITIONAL VALUE 000 



Ci'isco are absorbed at rates comparable to those of the natural fats. It is 

 only in the case of hydi'ogenated fats having melting jxjints above 50°C 

 that a retardation in absorption rate becomes evident. 



d. The Nutritional Value of Animal vs. Vegetable Fats. There has been 

 consideral)le discussion in the literature as to whether or not animal fats 

 are superior to vegetable fats as shown by the several physiologic indices 

 which are used for establishing nutritional value. Most of the work has 

 centered around a comparison of the nutritional value of butter as con- 

 trasted with that of vegetable fats, including vegetable fats modified by 

 hydrogenation. A number of different criteria have been employed for 

 making this comparison, but growth-promoting effect, pregnancy, and lacta- 

 tion, and the effect in multigeneration experiments, have been the princi- 

 pal methods for attacking this problem. 



(a) Relative Nutritional Value Based upon Growth Tests, a'. Experi- 

 ments on Normal Rats : There has been a long-continued discussion on the 

 question of whether or not butterfat per se possesses a specific nutritional 

 value not shared by other animal fats or by vegetable fats. On the positive 

 side of this discussion the more recent work has centered around the report 

 of Schantz, Elvehjem, and Hart^^^ in 1040, which stated that rats grew 

 better over the period of six weeks following weaning if they received a 

 liquid diet of skim milk homogenized with butterfat as compared with 

 similar diets in which corn oil, cottonseed oil, coconut oil, or soybean oil 

 was employed in place of butterfat. This difference in growth-promoting 

 capacity disappeared after a period of six weeks. It was later reported 

 from the same laboratory^"" ■^''i that the saturated fatty acids of the butter- 

 fat compose the effective fraction, and afford more growth than does a 

 comparable amount of whole butter. The volatile and unsaturated fatty 

 acid fractions were found to be ineffective in producing a greater augmenta- 

 tion of growth. However, the unsaturated fatty acids were found to be- 

 come active in promoting growth, after they had been hydrogenated. The 

 greater rate of growth reported in the earlier experiments of Schantz and 

 co-workers^^^ was ascribed to the presence of certain undefined long-chain 

 fatty acids which were believed to be in butterfat^™ but not in other fats.^^^ 

 However, two different groups of workers^"- -^"^ have failed to confirm the 



""^ E. J. Schantz, C. A. Elvehjem, and E. B. Hart, /. Dairy Sci., 23, 181-189 (1940). 



^ E. J. Schantz, R. K. Boutwell, C. A. Elvehjem, and E. B. Hart, /. Dairy Sci., 23, 

 1205-1210(1940). 



301 R. K. Boutwell, R. P. Geyer, C. A. Elvehjem, and E. B. Hart, /. Dairy Sci., 24, 

 1027-1034(1941). 



^^ K. M. Henry, S. K. Kon, T. P. Hilditch, and M. L. Meara, /. Dairy Research, 14, 

 45-58(1945). 



^^ E. L. Jack, J. L. Henderson, D. F. Reid, and S. Lepkovsky, /. Nutrition, 30, 175-181 

 (1945). 



