Refuse figures in table 2 likewise were taken from Circular 549 with 

 few exceptions. These data were used in converting from an "edible 

 portion'' to an "as purchased" basis. 



Minerals. — Mineral values were drawn from several sources. 

 Among them was the unpublished table prepared in 1941 by the Bureau 

 of Human Nutrition and Home Economics. 2 These values repre- 

 sented a careful study and evaluation of original data, published and 

 unpublished. The published investigations of H. C. Sherman 3 also 

 supplied many of the figures. Exceptions have been made in certain 

 cases where there was reason to believe that the published figures were 

 out of line with present knowledge. Mineral values for components of 

 the Army ration were obtained in most cases from special analyses. 



For foods not included in the above sources, mineral values were ob- 

 tained by averaging available data in the literature or were imputed 

 from a similar food (as tangerines from oranges), or from another form 

 of the same food (as canned from fresh). 



The calcium content of foods containing a fairly high concentration 

 of oxalic acid is given in footnotes because in these foods it may not be 

 nutritionally available. The concentration of oxalic acid reported for 

 any one food, although variable, may be high enough to combine with 

 all the calcium present to form insoluble calcium oxalate. Many foods 

 have been found to contain at least small amounts of oxalic acid, but 

 in these tables the calcium unless otherwise indicated has been con- 

 sidered completely available. 



Likewise the iron values given here represent total iron although ex- 

 perimental evidence suggests that the iron in some foods may be only 

 partially available. 



Vitamins. — Vitamin values have been obtained from a thorough 

 review of available published and unpublished data. Although they 

 are believed to be the most representative values obtainable at this 

 time, many will need revision as methods are further refined and addi- 

 tional data are reported. 



Vitamin A averages present a particular problem because substances 

 with vitamin A activity in the body may exist in foods either as pre- 

 formed vitamin A or as so-called precursors (carotene in its active forms 

 and cryptoxanthin). The problem is further complicated by difficul- 

 ties in the separation of vitamin A-active and nonactive carotenoid 

 pigments in some of the current methods of assay. Some investigators 

 report separate figures for the different kinds of carotenoids present, 

 others report total carotene, and still others express results in terms of 

 International Units of vitamin A, having made the conversion them- 

 selves. 



In these tables the vitamin A values are expressed in terms of Inter- 

 national Units. When the carotene content of foods was reported, the 

 values were converted into International Units on the basis that one 

 I. U. of vitamin A is equivalent to 0.6 micrograms of beta carotene or 

 1.2 micrograms of other vitamin A-active carotenoids. Further re- 

 search in this field may call for some revision in vitamin A values de- 

 rived from physical and chemical determinations, particularly with 



2 Bureau of Human Nutrition and Home Economics, minerals in foods: calcium, phosphorus, 



and iron in 64 food items. (Unpublished.) 



3 Sherman, H. C. chemistry of food and nutrition. Ed. 6, 611 pp., illus. 1941. 



