cal

any of several units of heat defined as the amount of heat required to raise the temperature of 1 kilogram of water by 1 degree Celsius (1°C) at a specified temperature. The calorie used in chemistry and biochemistry is equal to 4.184 joules. Symbol cal. See also nutrition.

In referring to the energy content of foods it is customary to use the “large calorie,” which is equal to 1 kilocalorie (kcal). Every bodily process, including the building up of cells, motion of the muscles, and the maintenance of body temperature, requires energy, which the body derives from the food it consumes. Digestive processes reduce food to usable “fuel,” which the body “burns” in the complex chemical reactions that sustain life. The amount of energy required for these chemical processes varies. Factors such as weight, age, activity, and metabolic rate determine a person's daily calorie requirement. Nutrition experts have computed daily calorie requirements in terms of age and other factors. These tabulations serve only as guides; they cannot, of course, embrace all individual variations.

From its daily intake of energy foods, the body uses only the amount it needs for energy purposes. The remainder is stored as fat. If the average adult consumes more calories than the daily requirement, he or she will gain weight. However, if consumption is less than recommended daily requirements, the body will supplement its energy sources by drawing upon stores of fat and the person will lose weight.