Calories Equal Energy
Excerpt from Eat Better, Live Better
This article starts below.
Food, like other forms of fuel, produces energy when it is oxidized (in our case, used by the body). This energy is released in units called calories.
Calories in food
Different foods supply different amounts of energy, and so have different caloric values. Fat supplies 9 calories per gram, carbohydrate and protein supply 4 calories per gram, and water and cellulose (fiber) no calories. That is why foods high in fat are highest in calories, and foods high in fiber and water (such as fresh vegetables) are lowest.
Weight loss equation
When a person eats just the amount of food or calories that he needs, all the food energy will be used. But when a person eats more calories than are needed, the excess energy is stored in the body as fat. This is also true when the excess is carbohydrates or protein; the liver converts the excess to fat. When a person eats fewer calories than are needed, the body converts its fat stores to energy to make up the difference, and weight is lost.
A desirable body weight depends on balancing energy intake -- determined by food choices -- with energy output -- determined by one's basal metabolism (energy needs of the body at rest) plus level of physical activity. The number of calories an individual needs every day depends on age, sex, size and level of physical activity.
We should not only stay within the optimum caloric levels to maintain ideal body weight, but if we are cutting down on calories, we should also select food of greater nutrient density (most nutrients per calorie). The way to control body weight is by balancing food intake against physical activity.