Great question—let's clarify this essential concept.
A calorie is a unit of energy. In nutrition, food energy is measured in kilocalories (kcal), where 1 kcal equals 1,000 calories. These provide the fuel your body needs for daily functions. Consume more energy than required, and it's stored as fat; too little, and you risk excessive leanness. Note that when people say 'calories,' they usually mean kilocalories.
