432 CARNEGIE INSTITUTION OF WASHINGTON. 



NUTRITION. 



Osborne, T. B., and L. B. Mendel, New Haven, Connecticut. Continuation 

 and extension of ivork on vegetable proteins. (For previous reports see 

 Year Books Nos. 3-19.) 



In our report for 1919 we described the preparation of a fraction 

 from yeast which was free from protein, fats, reducing carbohydrates, 

 and vitamins A and C, and so rich in water-soluble vitamin B that 

 daily doses of even so little as 16 milligrams sufficed to promote the 

 growth of young rats at a normal rate. The possession of this prod- 

 uct has made it possible to prepare diets of purified food substances 

 without the introduction of such large amounts of substances of 

 unknown nature as is the case when yeast or some other natural food 

 product was used to supply this vitamin. Furthermore, the demon- 

 stration that small quantities of dried alfalfa suffice to furnish the 

 daily requirement of vitamin A and latterly our observation that 

 the same can doubtless be attained by feeding daily a few milligrams 

 of a concentrate from cod-liver oil or from green leaves make it possible 

 to construct dietaries in which fat per se is at most a minimal con- 

 tamination of the ration. 



By supplying the vitamins in concentrated forms we have studied 

 the nutritive value of diets which were essentially devoid of true fats. 

 Some years ago we reported that young rats could make satisfactory 

 growth on diets free from fats. At that time the need of the fat- 

 soluble vitamin A for prolonged normal growth was not recognized 

 and as the experiments were terminated after a few weeks they have 

 been subjected to criticism by some investigators. We have there- 

 fore repeated these experiments under conditions which subsequent 

 experience had shown to be essential for growth during long periods. 

 The food mixtures first used consisted of lean meat thoroughly ex- 

 tracted with boiling water, starch, inorganic salts, together with 

 small quantities of alfalfa and dried brewery yeast respectively furnish- 

 ing the vitamins A and B. Analyses of the rations showed that the 

 maximum intake of fat at any time did not exceed 0.3 per cent of the 

 food eaten. Inasmuch as all the animals starting on this "fat-free" 

 diet with a body-weight of approximately 70 grams quadrupled their 

 weight within the usual time, while appearing as well nourished as 

 companion rats on diets containing liberal portions of butter fat or 

 lard, we conclude that if true fats are essential for nutrition during 

 growth the minimum necessary must be exceedingly^ small. 



The foregoing experimental data are corroborated by the growth 

 which has been observed in animals on diets in which both fat and 

 carbohydrate are practically lacking. These will be considered in 

 detail later. Unless a minute amount of fat plays as important a 

 role in the metabolism of the organism as do the minute quantities 



