A calorie is simply a measure of heat energy. Because food releases energy as it burns inside the body, the more calories a food contains, the more energy it will release. Body-fat is stored energy, much like a reserve gas tank for your car. Each pound of fat contains 3,500 calories. Think of your body's calorie balance much like your bank account. When the amount of energy you consume in a day is equal to the amount of energy you consume, nothing changes - the account stays the same. When your caloric expenditure exceeds your intake, however, your body-fat balance decreases. Conversely, when your intake exceeds your expenditure you will add calories in the form of fat. This may seem obvious but it underscores a fundamental truth about nutrition - calories count. You cannot outsmart this fact by cutting carbs to lose weight or increasing protein to build muscle. Regardless of what else you do, you simply must get the calorie balance right in order to maintain a healthy level of body-fat.