FACTORS INFLUENCING B VITAMIN REQUIREMENTS 277 



dextrin diets or high protein -low fat diets. In experiments with rats it has 

 also been found that diets containing dextrin as the carbohydrate require 

 less pyridoxine than diets in which sucrose is the carbohydrate com- 

 ponent. 01 



Effect of Proteins and Amino Acids. Much attention has been drawn 

 to the effects of protein levels on the riboflavin requirement. Reference 

 has previously been made to the studies of Czaczkes and Guggenheim 62 

 on the correlation of the dietary requirements of rats for riboflavin with 

 tissue and urinary riboflavin levels. In this study it was found that the 

 fat or protein content of the diet profoundly affected the requirement. 

 These results are summarized in Table 12. It is apparent that at least 

 part of this variation is due to variation in bacterial synthesis in the 

 gut, and it seems doubtful whether increased protein increases the ribo- 

 flavin requirement beyond this. Trufanov 63 has found that in rats on a 

 low protein diet the riboflavin content of the urine increases, while that 

 of liver and muscle decreases. He claims moreover that there is no further 

 synthesis of flavin-adenine-dinucleotide in the liver and tissues after fifty 

 days on this diet. There is little apparent relationship between these data 

 and the observation that thiamine and riboflavin tend to counteract the 

 degenerative changes wrought upon the liver and spleen of experimental 

 animals by protein-free diets. 64 



Table 12. The Effect of Protein on the Riboflavin Requirement of the Rat. 



% of Calories as Daily Riboflavin Riboflavin 



Diet ; — Riboflavin _ Level Level Remarks 



Fat Protein Excretion in Organs in Feces 



Standard 20% 20% 



High-fat 40% 20% diminished diminished diminished Requires two times 



amount of ribofla- 

 vin required to 

 maintain normal 

 level in organs. 



Low-fat 2% 20% increased increased increased Requires half of 



normal amount. 



High-protein 20% 34% diminished diminished diminished Requires twice nor- 

 mal amount. 



Low-protein 20% 11% no change no change no change Lack ability to store 



riboflavin. 



Our present understanding of the function of vitamin B 6 in amino acid 

 metabolism * would lead one to predict that an increased dietary protein 

 level would increase the vitamin B 6 requirement and this is found to be 

 the case. Thus, in mice on a vitamin B 6 -deficient 50 per cent casein diet, 

 the liver vitamin B c after 3 weeks was 0.97 /ug/gm, whereas in a similar 

 series on 10 per cent casein, the level was 3.7 /^g/gm and reached the low 



* Lyman's studies of bacteria are particularly interesting in this regard. 65 For 

 instance, with pyridoxine present, L. arabinosus loses its nutritional requirements for 

 threonine, lysine, and alanine. 



