Diet - calories

Alternative names  
Calories - diet


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

Technically, one calorie is the amount of energy required to raise the temperature of 1 gram of water 1 degree Centigrade (from 14.5 to 15.5). 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 one kilogram of water (about 2.2 pounds) one degree Centigrade.

Different foods can be used by the body to produce 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 calorie by definition.
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.


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.

Food Sources

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

Side Effects

  • 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.

See balanced diet.

Recommendations for limiting calories:

  • Do not eat meat more than once a day. Fish and poultry are recommended instead of red or processed meats because they are less fattening.  
  • Avoid frying food because your food absorbs the fats from the cooking oils and this increases your dietary fat intake. Bake or broil food instead. If you do fry, use polyunsaturated oils, such as corn oil.  
  • Cut down on your salt intake, whether it be table salt, or flavor intensifiers that contain salt such as monosodium glutamate (MSG).  
  • Include adequate fiber in your diet. Fiber is found in green leafy vegetables, fruit, beans, bran flakes, nuts, root vegetables, and whole grain foods.  
  • Do not eat more than 4 eggs per week. Although they are a good source of protein and low in saturated fat, eggs are very high in cholesterol, and should be eaten in moderation for that reason.  
  • Choose fresh fruit for desserts rather than cookies, cake, or pudding.  
  • Too much of anything has its drawbacks, whether it be calories, or a particular type of food. A well-balanced diet with creativity and variety are best suited to your needs.

Ask a registered dietician to help you calculate the amount of calories your body needs.

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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