The energy stored in food is measured in terms of calories.

Technically, 1 calorie is the amount of energy required to raise the temperature of 1 gram of water 1 degree Centigrade. The calorie measure used commonly to discuss the energy content of food is actually a kilocalorie or 1000 real calories. This is the amount of energy required to raise 1 kilogram of water (about 2.2 pounds) 1 degree Centigrade.

Different foods contain different amounts of energy -- which is why a small piece of chocolate can have many more calories than a similarly sized piece of lettuce.

However, since calories are a measure of energy, there cannot be, as some diet books claim, different types of calories. A fat calorie has the same amount of energy as a protein or carbohydrate calorie.

A person's caloric need is determined using a variety of mathematical equations. Age, height, current weight, desired weight, and height are taken into account. Diet is what you eat. Dieting usually refers to eating less calories to lose weight. 

The amount of calories in a diet refers to how much energy the diet can provide for the body. A well-balanced diet is one that delivers an adequate amount of calories while providing the maximum amount of nutrients.

The body breaks down food molecules to release the energy stored within them. This energy is needed for vital functions like movement, thought, growth -- anything that you do requires the use of fuel. The body stores energy it does not need in the form of fat cells for future use.

The process of breaking down food for use as energy is called metabolism. Increased activity results in increased metabolism as the body needs more fuel. The opposite is also true. With decreased activity the body continues to store energy in fat cells and does not use it up. Therefore, weight gain is the result of increased intake of food, decreased activity, or both.

The nutrition labels on food packages indicate the number of calories contained in the food.

Naturally, different foods provide different amounts of calories. Some foods, such as ice-cream, have many calories; while others, like leafy vegetables, have few.

• Inappropriate dieting (fad dieting) can lead to rebound weight gain.
• Altered body image can lead to anorexia nervosa or bulimia.
• Diets that are excessively low in calories are considered dangerous and do not result in healthful weight loss. A more desirable method of weight reduction is one that is moderate in calories and that encourages routine exercise.
• Children and young adults should not limit calories below the Recommended Daily Allowance because they require a certain amount of calories for growth and development. Better eating habits for the entire family often accomplish the caloric decrease that is required for a child or young adult to reach a desirable weight.