X. REQUIREMENTS 319 



the dietary intake of this acid.'--" Bernhard et al}^ and Sehoenheimer'^ 

 found that tissue linoleic and Hnolenic acids incorporated deuterium from 

 the body water enriched with heavy water at a much lower rate than did 

 the other fatty acids, suggesting that the animal does not synthesize essen- 

 tial acids. On the other hand, studies using spectrophotometric techniques 

 for the measurement of the unsaturated acids seem to indicate synthesis of 

 small amounts of essential fatty acids by animals on a fat-deficient diet. 

 Medes and Keller" found that rats synthesized polyunsaturated fatty 

 acids when diets deficient in Be and fat were supplemented with vitamin 

 Be . In their studies on fat deficiency in adult rats, Barki et al. found spon- 

 taneous cures and demonstrated that the essential fatty acid content of the 

 animals rose when they recovered spontaneously.'^ The discrepancies 

 between the deuterium experiments and these latter observations were 

 probably due to the relatively short-term nature of the deuterium experi- 

 ments and the apparent slow rate of turnover of the polyunsaturated fatty 

 acids. It appears that the essential fatty acids can be synthesized by the 

 animal, but not in sufficient cjuantity to provide for the needs of the growing 

 animal. 



B. HUMAN BEINGS 



There is no specific information regarding the essentiality of linoleic acid, 

 or similar unsaturated fatty acids, in human nutrition. The evidence indi- 

 cates that these fatty acids may be essential, that the requirement is rela- 

 tively small, and that ordinary diets easily supply this requirement. The 

 Food and Nutrition Board of the National Research Council recommends 

 that an adequate diet should contain essential fatty acids to the extent of 

 1 % of the total calories. 



12 N. R. Ellis and O. G. Hankins, /. Biol. Chem. 66, 101 (1925). 



13 A. Banks, T. P. Hilditch, and E. C. Jones, Biochem. J. 27, 1375 (1933). 

 1* H. E. Longenecker, J. Biol. Chem. 128, 645 (1939). 



15 K. Bernhard, H. Steinhauser, and F. Bullet, Helv. Chim. Acta 25, 83 (1942). 



18 R. Schoenheimer, The Dynamic State of Body Constituents, p. 18. Harvard Uni- 

 versity Press, Cambridge, Mass., 1949. » 



1' G. Medes and D. C. Keller, Arch. Biochem. 15, 19 (1947). 



18 V. H. Barki, R. A. Collins, E. B. Hart, and C. A. Elvehjem, Proc. Soc. Exptl. 

 Biol. Med. 71,694 (1949). 



