Explanation Of Headings

Food as purchased may or may not consist entirely of edible material. When an article of food contains inedible matter or refuse, this may be stated separately and the composition of the edible portion then given, or the percentages of refuse and of edible nutrients in the original matter may be given so as to show directly the percentage of each edible nutrient obtained in the material as purchased. For example; 100 pounds of beef contains 16 pounds of bone and 84 pounds of moist flesh, of which 15.4 pounds are protein, 15 pounds fat, 53 pounds water, and 0.6 pound ash. The composition may be stated in either of the following forms:

Composition Of Beef

For most purposes it is convenient to include in one table the nutrients calculated both on the basis of edible material and of material as purchased. In such a case the percentage of refuse in the material as purchased may be given or may be omitted as in the following form:

Composition Of Beef

In order to avoid confusion and possible errors in taking data from tables of composition it is important to note in which form the percentages are stated. Data given in either form are of course readily convertible into the other. In Table I which follows, the percentages of nutrients and the corresponding energy values are stated in the form last illustrated above. Table II shows percentages of ash constituents in the edible portion only. Table III shows grams of protein and of calcium, phosphorus, and iron in 100-Calorie portions, which estimates may obviously be used equally well whether the food be originally recorded in terms of edible material or of material as purchased.

A word of explanation regarding the sources and reliability of the data may also be offered. The percentages of proteins, fats, and carbohydrates given in Table I are in the great majority of cases taken from the tables of composition of American food materials compiled by Atwater and Bryant and published in Bulletin 28 of the Office of Experiment Stations, U. S. Department of Agriculture. By reference to this bulletin the reader may find the number of analyses on which the average is based and the maximum and minimum of the recorded percentages of each constituent, as well as the percentages of moisture, ash, and in some cases crude fiber. The energy values given in Table I are computed from the average percentage of protein, fat, and carbohydrate by the use of the latest and most accurate factors (see page 143). The data for ash constituents given in Tables II and III are based on a critical compilation of all available ash analyses, both American and European. In some cases only a single ash analysis could be found; in other cases the data given are averages of many fairly concordant analyses. Between these extremes are data of all degrees of probable reliability. It does not seem feasible to indicate the relative accuracy of the estimates for different articles of food. In general it may be said that only in the cases of the more important foods are the ash analyses as yet sufficiently numerous and concordant to justify one in laying great emphasis upon comparisons of one article of food with another. More emphasis can properly be laid upon estimates of the ash constituents of rations or dietaries made up of several food materials, since in such cases accidental errors will tend to offset each other. It is chiefly to facilitate such calculations that the tables have been made as complete as seemed practicable even though this necessitated including estimates of differing reliability on apparently equal terms.

Data which are based in part at least upon assumptions are inclosed in parenthesis. They are not necessarily less accurate as estimates of average composition than are some of the directly determined data of individual analyses.

Since many unpublished ash analyses have been included in the present averages, Tables II and III will be found to present many differences in detail from those published elsewhere, or in the first edition of this book. The general trend of the averages has, however, not been materially altered by the results of recent work.

Attention may also be called to the fact that in Table II the data are uniformly given as percentages of the elements and not of their oxides. For the convenience of those who may prefer to continue to calculate calcium and phosphorus in terms of the oxides as has been customary in the past, Table III shows the weights of CaO and P2O5 as well as of protein, calcium, phosphorus, and iron in 100-Calorie portions of foods.