Rather obviously, low calorie diet depends on the fact that in order to lose weight, it is important to eat fewer calories than you actually use.
Definition of a calorie?
A calorie is a measurement of the energy provided by food. The calorie is the amount of heat required to raise 1 kilogram of water 1 degree centigrade. If your meal has more calories, then it will will give you a larger amount of energy when it is eaten.
Examples of low calorie foods include bok choy, tomatoes, grapefruit, steaks and burgers, and eggs.