Calorie

The name calorie is used for two units of energy.

Although these units are part of the metric system, they have been superseded in the International System of Units by the joule. One small calorie is approximately 4.2 joules (so one large calorie is about 4.2 kilojoules). The factor used to convert calories to joules at a given temperature is numerically equivalent to the specific heat capacity of water expressed in joules per kelvin per gram or per kilogram. The precise conversion factor depends on the definition adopted.

In spite of its non-official status, the large calorie is still widely used as a unit of food energy. The small calorie is also often used for measurements in chemistry, although the amounts involved are typically recorded in kilocalories.

Food energy

Food energy is chemical energy that animals (including humans) derive from their food and molecular oxygen through the process of cellular respiration. (Cellular respiration involves either the process of joining oxygen from air with the molecules of food (aerobic respiration) or the process of reorganizing the atoms within the molecules (anaerobic respiration).)

Humans and other animals need a minimum intake of food energy to sustain their metabolism and to drive their muscles. Foods are composed chiefly of carbohydrates, fats, proteins, water, vitamins, and minerals. Carbohydrates, fats, proteins, and water represent virtually all the weight of food, with vitamins and minerals making up only a small percentage of the weight. (Carbohydrates, fats, and proteins comprise ninety percent of the dry weight of foods.) Organisms derive food energy from carbohydrates, fats and proteins as well as from organic acids, polyols, and ethanol present in the diet. Some diet components that provide little or no food energy, such as water, minerals, vitamins, cholesterol, and fibre, may still be necessary to health and survival for other reasons. Water, minerals, vitamins, and cholesterol are not broken down (they are used by the body in the form in which they are absorbed) and so cannot be used for energy. Fiber, a type of carbohydrate, cannot be completely digested by the human body. Ruminants can extract food energy from the respiration of cellulose because of bacteria in their rumens.

Calorie (disambiguation)

A calorie is an old unit of energy, now superseded by the joule.

Calorie may also mean: