Calories are a measure of energy. They factor into weight gain or loss because excess energy taken in is stored as fat. Diet and exercise change the balance of stored energy.
Definition
The scientific definition of a calorie is the amount of energy required to heat 1g of water 1 degree Celsius. A calorie as conventionally measured, such as by exercise machines or on food, is actually a kilocalorie, or 1,000 calories.
Calories and Weight
It takes approximately 3,500 calories in excess to be stored as 1 lb. fat, and 3,500 calories of activity over the food intake to burn 1 lb. of fat. Weight loss or gain depends on the balance of calories taken in from food, and the balance of calories burned throughout the day. The more activity, the more calories you burn.
Modifying Calories
Calories, or energy storage and use, is determined by the balance of activity and diet. Increasing activity levels through exercise increases the calories burned. Likewise, increasing food intake increases the fat stored if the calories are not used for exercise.
References
- "Nutrition: Concepts and Controversies"; Frances Sizer and Ellie Whitney; 2007
- "General Chemistry: Principles and Modern Applications"; Ralph H. Petrucci et al; 2010
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