INTRODUCTION 837 



membranes. Fats also serve as a mechanical protection for nerves and 

 for bonj^ projections. The la^^er of subcutaneous fat is undoubtedly of 

 considerable importance in maintaining body temperature, particularly 

 because of its function as an insulator. Adipose tissue, in addition to 

 connective tissue, acts as a protective covering for organs such as kidneys 

 and ovaries, which are frequently imbedded in large amounts of storage 

 fat. Finally, the capability of fat deposits to furnish energy over long 

 periods of time of fasting is another most important function which should 

 not be overlooked. 



Fats and oils are generally considered to have the same type of composi- 

 tion. Both are fatty acid esters of the trihydric alcohol, glycerol. The 

 term "fats" is usually accepted as referring to substances solid at ordinary 

 temperatures, while "oils" are products which are liquid under certain 

 conditions. The terms are not necessarily absolute; one must recognize 

 that a compound which is a fat under one environmental condition may 

 be an oil under different temperature conditions. However, one should 

 distinguish between "fats" and "fatty foods." Most of the fats of com- 

 merce contain not only the triglycerides but also other substances which 

 are dissolved in the fats. These comprise chiefly the non-saponifiable 

 fraction, and contain sterols, tocopherols (vitamins E), carotenoids and, 

 in some cases, vitamin A. In the case of crude fats, phospholipids fre- 

 quently also comprise an appreciable proportion of the material, although 

 these are usually almost completely removed in the processes of refining. 

 One should also include in the category of "fatty foods" substances such 

 as butter and margarine in which triglyceride fats comprise only about 

 80% of the total material, the balance being made up of non-fat milk 

 solids, water, salt, fat-soluble vitamins, and other materials. It is ob- 

 vious that some of the materials frequently considered as nutritional 

 components of the fats are actually present in solution in the fats and are 

 not really part of them. The only substances having an absolute nutri- 

 tional value which is part of the triglyceride molecule are the essential 

 fatty acids. The nutritional significance of the fats has been discussed 

 in a number of other publications by the present author.*"^ The physi- 



'' H. J. Deuel, Jr., Nutrition Aspects of Cottonseed Oil Utilization, in A. E. Bailey, 

 Cottonseed and Cottonseed Products, Interscience, New York, 1948, pp. 7G3-811. 



^ H. J. Deuel, Jr., Nutritional Value of Soybeans and Soybean Products, in K. S. 

 Markley, Soybeans and Soybean Products, Vol. II, Chap. 18, Interscience, New York, 

 1«)51, pp. 727-780. 



^ H. J. Deuel, Jr., and S. M. Greenberg, Sonic Biocheniiral and Nutritional Aspects in 

 Fat Chemistry, Fortschr. Chem. org. Natursloffe, 6, 1-8G (1950). 



' H. J. Deuel, Jr., in R. T. Holman, W. O. Lundberg, and T. Malkin, Progress in the 

 Chemistry of Fats and Other Lipids, Vol. 2, Pergamon Press, London, 1954, pp. 99-192. 



8 H. J. Deuel, Jr., Federation Proc, 14, 639-649 (1955). 



