Energy human caloric requirements

This unit, which is always written with a small c, is the amount of energy heat required to raise the temperature of 1 gram of water 1° C (precisely from 14.5 to 15.5 C). It is equivalent to 4.184 joules. In popular writings, especially those concerned with human caloric requirements, the term calorie is frequently used erroneously for the Kilocalorie (k-calorie or kcal). 

Feron et al. (1990) have concluded that, in general, adjustment for differences in body size between experimental animals and humans should be based on caloric requirement (energy metabolism) as this was considered to be both scientifically sound and of practical significance. 

Fats and oils have major roles in human nutrition. They are concentrated dietary sources of energy, providing approximately 9 kcal/g when metabolized compared with 4 kcal/g for carbohydrates and proteins, and account for about 36 percent of domestic caloric intake per capita.19 Dietary lipids also can provide essential molecular structures that are synthesized by the body into compounds required for selective functioning of cell membranes and regulation of life processes. 

In the normal human diet, about 25% to 50% of the caloric intake consists of fats and oils. These substances are the most concentrated form of food energy in our diet. When metabolized, fats produce about 9.5 kcal of energy per gram. Carbohydrates and proteins produce less than half this amount. For this reason, animals tend to build up fat deposits as a reserve source of energy. They do this, of course, only when their food intake exceeds their energy requirements. In times of starvation, the body metabolizes these stored fats. Even so, some fats are required by animals for bodily insulation and as a protective sheath aroimd some vital organs. 

By 1900 the caloric value of foods had been carefully determined. Between 1890 and 1900 efforts were made to study food requirements by statistical methods. Dietary studies were conducted in several parts of the world, diets being evaluated for energy and protein according to standards developed by Voit and Atwater. Data collected by Atwater in the United States represent, as stated by McCollum, an epoch in development of knowledge of human nutrition. ... 

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