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THE PRINCIPAL CONSTITUENTS AND FUNCTIONS OF FOOD
Foods and Food Values
Through the food the body obtains the substances which enter into its structure, which yield energy for its activities, and which regulate the processes essential to life and health.
Most articles of food contain water, as shown by the fact that they lose weight on drying. The dry residue consists mainly of combustible matters (organic substances), but when these are burned, there usually remains more or less ash (a mixture of inorganic or mineral substances).
The combustible portion of the food may comprise a variety of organic compounds, but in the great majority of staple foods most of the organic matter is found to be comprised within three groups of substances — the carbohydrates (such as the starches and sugars), the fats (such as those of butter, olive oil, corn oil, lard, and meat fat), and the proteins (such as the albumin of egg, the curd of milk or cheese, the muscle fiber of meat, the gluten of flour or bread).
In most cases if the percentages of proteins, fats, carbohydrates, mineral matters, and water in a food be determined accurately, it will be found that these groups of substances make up nearly the entire weight of the food. For many purposes it is sufficient to analyze foods as if they consisted entirely of these five parts, ignoring the minor constituents and letting them be