DIGESTION, ABSORPTION, AND DIGESTIBILITY 431 



c. Factors Altering the Digestibility of /3-Carotene and of Other Ca- 

 rotenoids. The same factors which influence the absorption of /3-carotene 

 are operative in respect to the digestibility of this provitamin. The diges- 

 tibility of the carotenoids is usually not complete, even when they are given 

 in minimal quantities, and some unabsorbed carotenoid is usually present 

 in the feces. Because of the limited capacity for absorption, the value for 

 the coefficient of digestibility decreases with an increased intake of the 

 carotenoids. Thus, Kemmerer and Fraps^*^ found that, when rats were fed 

 /3-carotene in dehydrated alfalfa at levels of 1, 10.5, and 20 parts per mil- 

 lion, digestibilities of 43%, 22%, and 18 to 23%, respectively, were observed 

 When chickens were employed as test animals, figures of 69% and 29% 

 were obtained for the digestibility when the diet contained, respectively, 1 

 and 20 parts of /3-carotene per million. 



A number of factors other than the cjuantity of /3-carotene administered 

 affect the extent of digestibility. When /3-carotene was given with a fat- 

 free diet to human subjects, Kreula^^ noted a digestibility of only 10%, as 

 contrasted with a value of 50% when the provitamin was administered in 

 a single dose in olive oil, and one of 70% when the oil solution was given in 

 divided doses. Kemmerer and Fraps^" observed digestibility figures of 51% 

 and 22%, respectively, for jS-carotene when administered to rats in oil or in 

 dried alfalfa fed with a fat-free regimen. Wilson and collaborators^' 

 reported a digestibility for carotene of 90% when given in raw or cooked 

 carrots or in cooked spinach with fat, while the value was only 50% when 

 it was given without fat. Other values for the digestibility of /3-carotene 

 include the following: from carrots (van Eekelen and Pannevis^*) 1%, and 

 from spinach, 5%; from purees of tomatoes, carrots, spinach, and carrot 

 meal (With^^), 30 to 60%; from carrots (Accessory Food Factors Com- 

 mittee^) 25%, and from spinach, 40%. According to Kreula and Virtanen,*^ 

 20% of carotene in finely-grated raw carrot was lost during passage through 

 the digestive tract, 5% of that from coarsely-grated raw or cooked carrots. 



80 A. R. Kemmerer and G. S. Fraps, /. Nutrition, 16, 309-315 (1938). 



81 M. S. Kreula, Biochem. J., 41, 269-273 (1947). 



82 H. E. C. Wilson, S. M. Das-Gupta, and B. Ahmad, Indian J. Med. Research, 24, 

 807-811 (1937). 



83 M. van Eekelen and W. Pannevis, Nature, I4I, 203-204 (1938). 



8* T. K. With, Absorption, Metabolism, and Storage of Vitamin A and Carotene, 

 Munksgaard, Copenhagen, 1940, and Milford, London, 1940, pp. 70, 90 ff.; also cited 

 by M. S. Kreula, Biochem. J., 4I, 269-273 (1947), p. 269. 



85 Report of the Vitamin A Subcommittee of the Accessory Food Factors Committee, 

 Lister Inst., Rep. Med. Research Council {Brit.), 1939-1945, pp. 107-109; H. M. Sta- 

 tionery Office, London, 1945. 



86 M. S. Kreula and A. I. Virtanen, Upsala. Lakereforen, Forh., 45, 355-362 (1939); 

 Chem. Abst.,34, 5897 (1940). 



