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.
The calorie measure used commonly to discuss the energy content of food is actually a kilocalorie or 1000 real Calories (note the capital C). This is the amount of energy required to raise 1 kilogram of water (about 2.2 pounds) 1 degree centigrade. So, while a can of Jolt Cola has 150 Calories, it also has 150,000 calories. Try telling someone you ate 3 million calories worth of food yesterday, and see what happens!
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. The caloric energy in what we eat comes from the fat, carbohydrates, and protein levels in foods. Each gram of fat provides 9 Calories, and each gram of carbohydrates and protein contribute 4 Calories. So, if you were to drink a bottle of Snapple, which contains about 58 grams of carbohydrates, you would get about 232 Calories.
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, and desired weight are taken into account. Diet is what you eat. Dieting usually refers to eating fewer calories to lose weight.
Function of calories:
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 and does not use it up. Therefore, weight gain is the result of increased intake of food, decreased activity, or both. Nutrition labels on food packages indicate the number of calories contained in the food.
You may think that the most of the calories you need go towards all the movement you do all day, but that's not true; the majority of the calories you get from food go to maintaining your body. Your body has what is called a Basal Metabolic Rate, which is the amount of calories your body needs just to keep going. In most people, about 60 percent of the calories you consume are used simply in keeping your body's tissues maintained and body processes like your digestive and cardiovascular systems working.
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