This section is from the book "Scientific American Reference Book. A Manual for the Office, Household and Shop", by Albert A. Hopkins, A. Russell Bond. Also available from Amazon: Scientific American Reference Book.
Food is used in the body to build and repair tissue and to furnish energy. The manner in which the valuable constituents are utilized in the body may be expressed in tabular form as follows:
Protein................................................. | Forms tissue (muscles, tendon, and probably fat). | All serve as fuel and yield energy in form of heat and muscular strength. |
White (albumen) of eggs, curd (casein) of milk, lean meat, gluten of wheat, etc. | ||
Fats................................. | Form fatty tissue. | |
Fat of meat, butter, olive oil, oils of corn and wheat, etc. | ||
Carbohydrates............................................ | Transformed into fat. | |
Sugar, starch, etc. | Aid in forming bone, assist in digestion, etc. | |
Mineral matters (ash).......................... | ||
Phosphates of lime, potash, soda, etc. |
Heat and muscular power are forms of force or energy. The energy is developed as the food is consumed in the body. The unit commonly used in this measurement is the calorie, the amount of heat which would raise the temperature of a pound of water 4 deg. Fahrenheit.
Instead of this unit some unit of mechanical energy might be used - for
 
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