276 THE BIOCHEMISTRY OF B VITAMINS 



particular effect. Conflicting reports exist in many cases, making a thor- 

 ough understanding of many relationships impossible, at least for the 

 present. The discussion which follows then is of necessity a brief one, 

 intended merely to point out the major associations of this type which are 

 recognized at present. 



Effect of Carbohydrates and the Calorific Intake. Thiamine functions 

 in the form of thiamine pyrophosphate (cocarboxylase) in the metabolism 

 of carbohydrates (the decarboxylation of pyruvate and ketoglutarate) 

 (p. 158) . For this reason the thiamine requirement is determined almost 

 completely by the carbohydrate intake. It is apparently immaterial to 

 the requirement whether the carbohydrate is used immediately for energy 

 or converted to fat. 55 Because of this, the thiamine requirement is fre- 

 quently expressed in terms of thiamine per Calorie, or even better per 

 "non-fat Calorie." Fat, and to a lesser extent protein, by displacing car- 

 bohydrate from the diet, exert a "sparing action" on the thiamine re- 

 quirement. 



Dann 56 has maintained rats for a period of a year on a substantially 

 thiamine-free diet containing 80 per cent protein and no carbohydrate. 

 At the end of this period, the animals appeared to be in excellent condi- 

 tion although they had not grown rapidly. In this case, it would appear 

 that intestinal synthesis by symbionts was ample to meet most require- 

 ments on the carbohydrate-free diet. 



Thiamine is not required in the immediate metabolism of ethyl alcohol, 

 although it was long believed otherwise; and thiamine deficiencies in 

 alcoholics are believed to be due to low intakes and possibly poor assimi- 

 lation. Lowry et al. 57 found in fact that alcohol delayed the symptoms of 

 an acute thiamine deficiency in rats on a deficiency diet, when it either 

 supplemented or replaced part of the carbohydrate of the diet. Westerfeld 

 and Doisy, 58 in similar studies with pigeons, found that either alcohol or 

 fat had a thiamine-sparing action, 16 grams of fat being equivalent in 

 this regard to 9 grams of alcohol. It therefore seems well established that 

 the isocaloric substitution of alcohol or fat for carbohydrate decreases 

 the thiamine requirement. Recent studies have also shown that replace- 

 ment of the dietary carbohydrate on an isocaloric basis with ethyl alcohol 

 results in an increased excretion of thiamine, N'-methylnicotinamide, and 

 pyridoxic acid, but not pantothenic or folic acid. 59 



High caloric diets also apparently create an increased folic acid require- 

 ment, and this adds to the many other difficulties inherent in assessing 

 the foli'c acid requirements of the chick (p. 248) . Luckey and co-workers 

 further found the nature of the diet to be a major factor. 60 Diets high 

 in fat or in which the only carbohydrate was glucose, sucrose or starch 

 necessitated a much higher level of folic acid than did cornmeal and 



