FATS AS ESSENTIAL DIETARY COMPONENTS 859 



of stearic acid can ho attriliutod to the failure of the latter acid to be 

 satisfactorily absorbed. 



Two recent American reports have indicated that the beneficial effect 

 of fat in thyrotoxicosis is not necessarily proportional to the essential 

 fatty acid content of the fats fed. Thus, Eishoff^'* demonstrated that the 

 growth retardation of rats treated with thyroid was counteracted equally 

 well ]\v olive oil, cottonseed oil, peaiuit oil, corn oil, soybean oil, hydro- 

 freiiated cottonseetl oil, ^^'heat germ oil, and lard, fats which are known to 

 haxe widely varying contents of the essential fatty actids. Although 

 growth inhil)ition was prevented, according to these tests, the fats failed 

 to counteract the inhibition of ovarian development or the increase in 

 renal, adrenal, and ventricular weight. In tests carried out by Green- 

 berg and DeueF^ the presence of cottonseed oil in the diet not only per- 

 mitted normal growth of the hyperthyroid rats but also decreased pre- 

 mature mortality. Thus, in the case of the male rats, the following gains- 

 in-weight and mortality rates were noted: low-fat diet alone, 162.2 g., 

 0%; low-fat with thyi-oid powder, 98.0 g., 50%; low-fat with thyroid 

 powder plus a high vitamin B12 level, 98.0 g., 83%; high-fat diet alone, 

 229.9 g., 0%; high-fat diet with thyroid powder, 230.4 g., 0%. Practi- 

 cally identical results were obtained in the case of female rats. Green- 

 berg" later reported that methyl linoleate and cottonseed oil were both 

 able to protect immature rats against growth retardation when the rat 

 was fed a fat-free diet to which 0.05% desiccated thyroid had been added. 

 Although 50 mg. of linoleate per day, or 500 mg. of cottonseed oil daily, 

 were largely able to counteract the growth retardation m the rat on the 

 fat-free diet to which thyroid powder had been added, these substances 

 were not able to protect the hyperthyroid rat against enlargement of the 

 heart, and protected it only partially against enlargement of the kidney. 

 Although Ershoff^^ was able to demonstrate direct correlation between the 

 fat content of the diet and the gain in body weight and length of survival 

 of immature h}' perthjToid rats, he also found that a defatted liver residue 

 was as effective as cottonseed oil, when fed at a 10% level in the diet, in 

 prolonging survival of the immature hyperthyroid rats on an otherwise 

 fat-free ration. This defatted liver residue was found to be more effective 

 than cottonseed oil in promoting gro^\i;h. 



Thus, although the beneficial effect of fat in hyperthyroidism may be 

 partly attributable to the essential fatty acid content, the requirements 

 for which might be increased in hyperthyroidism, and partly to the higher 



'« B. H. Ershofif, /. Nutrition, 39, 259-281 (1949). 

 " S. M. Greenberg, /. Nutrition. 47. 31-39 (1952). 



