Chemical Composition of Twenty-Two Common Foods and Comparison of Analytical with Calculated Values of Diets

Abstract

The analyses of twenty-two common foods for nitrogen, fat, energy, the positive (calcium, magnesium, sodium and potassium) and negative (phosphorus, chlorine and sulfur) minerals and iron indicate that individual samples of a given food vary from values reported in the standard tables. Fruits and vegetables vary widely while milk is more constant in mineral content. The variability of common foods does not seem to be as much a measure of contamination as a determination of real differences in composition. Comparison of a series of analyses of eleven composite diets with the sums of the corresponding values for the individual foods in the diet, emphasizes the increased accuracy which may be obtained when a larger amount of a given constituent is contained in the material available for analysis. The composite diets showed a more constant composition than the components. When the analyses of composite diets are compared with dietary figures calculated from the literature, there is good agreement in the content of magnesium, potassium, phosphorus, sulfur, calories and fat. Sodium, chlorine and calcium may be significantly different from calculated values. If mineral, energy or fat content of a composite diet or an individual food is to be known with the highest degree of accuracy, it should be analyzed under the conditions of the experiment in which it is to be used. The variations from time to time, as indicated by the standard error of the mean of each series, did not vary appreciably for a given constituent excepting in the case of sodium and chloride, even when the technique was refined in every possible manner. This indicates that the variations are inherent in the foods themselves rather than measures of errors in manipulation.