CONTENTS Xlll 



IV. The Digestion, Absorption, and Digestibility of Lipids Other than 

 Fats (continued) 



7. The Digestion, Absorption, and Transformation of the Carotenoids in 



the Gastrointestinal Tract 282 



( 1 ) The Absorption of Carotenoids from the Intestine 283 



a. The Absorption of /3-Carotene 283 



(a) Factors that Affect the Absorption of /3-Carotene 285 



a'. Surface Area and the Absorption of /3-Carotene 285 



b'. The Effect of Bile on the Absorption of /3-Carotene 286 



c'. The Effect of Simultaneous Fat Feeding on the Absorption 



of /3-Carotene 286 



d'. The Effect of Emulsifying Agents on the Absorption of /3- 



Carotene 288 



e'. The Effect of Thyroxine and Thiouracil on the Absorption 



of /3-Carotene 289 



f '. The Effect of Substances Fed Concomitantly with /3-Caro- 

 tene on Its Absorption 290 



g'. The Effect of Pteroylglutamic Acid 293 



b. The Absorption of a- and 7-Carotenes 293 



c. The Absorption of Lycopene 294 



d. The Absorption of Oxycarotenoids 294 



(a) Cryptoxanthin 294 



(b) Lutein 295 



(c) Zeaxanthin 296 



(d) Other Oxycarotenoids 296 



e. Stereoisomer^ Forms of Carotenoids 296 



(2) The Stability of /3-Carotene in the Intestine 297 



(3) The Digestibility of Carotenoids 300 



a. Factors Affecting the Digestibility of Carotenes 300 



(a) The Amount of Carotene Administered 300 



(b) The Effect of the Food Given Simultaneously with Carotene 301 



(c) The Effect of Thyroxine and Thiouracil 302 



(4) Changes in the Carotenoids in the Intestinal Wall 303 



a. The Transformation of Carotenoids into Vitamin A 304 



b. Sites for the Conversion of Carotene to Vitamin A Other Than 



the Small Intestine 306 



c. The Effect of the Thyroid Gland on the Transformation of Caro- 



tene to Vitamin A 307 



8. The Digestion and Absorption of Phytofluene in the Gastrointestinal 



Tract 310 



9. The Digestion, Absorption, and Transformations of the Fat-Soluble Vi- 



tamins 310 



(1) Vitamin A 310 



a. The Absorption of Vitamin A from the Intestine 310 



(a) Hydrolysis of Vitamin A Esters as a Preliminary to Absorp- 



tion 311 



(b) Factors Altering the Rate of Absorption of Vitamin A 312 



a'. The Effect of Age 312 



