Calories

Calories are units of energy. Although it is not considered a nutrient, energy is more important than other nutrients because without it, our bodies would grind to an immediate halt. Due to energy's essential nature, the body has become quite good at conserving it, and in times of scarcity, the ability can make the difference between those who survive and those who perish.

A calorie is defined as the amount of heat energy necessary to raise the temperature of 1 gram of water 1 degree Celsius. Technically, when we see the word "calorie" on a food label or in any nonscientific writing, it refers to a kilo calorie (kilo = 1,000), which is often abbreviated as kcal.

Fats, proteins, carbohydrates, and even alcohol are complex compounds that have a caloric value because it took energy to make them. When we metabolize or bum them, the energy is then released and used by the body. One gram of fat contains approximately 9 calories, and 1 gram of protein or carbohydrate contains 4 calories. A gram of alcohol contains 7 calories. Fats contain most calories because they give off the greatest amount of energy when metabolized.

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Excerpted from:

From The Nutrition Doctor's A-to-Z Food Counter. Copyright © Ed Blonz, 1999. Used by arrangement with NAL Signet, a member of Penguin Group (USA) Inc.

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