What is a Calorie?
Calories are simply the energy in food. Calories come from carbohydrates, protein, fat, and alcohol. There are no calories in vitamins and minerals or water. Fat has the most calories, with 9 calories per gram; alcohol provides 7 calories per gram, and protein and carbohydrate provide 4 calories per gram, although carbohydrate from fiber provides fewer calories because fiber is not completely absorbed.
Calorie requirements
Personal daily calorie requirements are based on gender, age, physical activity level, body composition, and genetics. Physically active young males with a large muscle mass require the most calories. The Dietary Guidelines for American recommends 45 – 65% of calories from carbohydrate, 10 – 35% of calories from protein, and 20 – 35% of calories from fat.
What happens when Calorie intake is too high?
When calorie intake exceeds calorie output, excess calories are stored in the form of body fat. The body stores fat to use for energy at times when calories are in short supply.
What happens when Calorie intake is too low?
When calorie intake is less than calorie output, the body breaks down stored fat to use for energy. The body also breaks down muscle mass for energy from protein. But when calorie intake is not extremely low, protein can be rebuilt at a rate that matches breakdown.
Source:http://caloriecount.about.com
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