A calorie is a measure of energy. It is scientifically described as being the amount of energy required to raise the temperature of one gram by one degree Celsius. Calories of a food can also be recognized as a kilocalorie, or one thousand-calorie unit.
In order for your body to grow, your body is required to have certain amounts of energy, or calories, depending on your age and height. For example, according to the Food and Nutrition Board of the National Research Council, women twenty-five to fifty years of age who are five feet, four inches tall and weigh 138 pounds, have a suggested 2200 calorie intake. For those of different height, weight, age, body size, physical condition, physical activity, and sex, your calorie intake may be different. Teenagers require more calories than full-grown adults do since teen's bodies are still growing and need that extra energy. Also, those who are more active will require more calories than those who are inactive.
You gain extra weight when the food you eat provides more calories than your body needs and the excess calories are stored as fats.
The number of calories you need to eat each day is determined by how much energy you need to maintain your lean mass and the internal functions of your body's processes. Since this is true, you are able to check how many calories your body needs by testing your Basal Metabolic Rate (BMR), which is the rate at which your body spends energy for maintenance activities each hour. You can do so by following these instructions taken from "Calories Required | BMR"
"A) Divide your weight by 2.2 ( = your weight in kilograms)
Multiply that number by the BMR factor (1 for a man, .9 for a woman)
Multiply that number by...