The process of gaining or losing weight can be explained by comparing your body to your car. Both run 【B1】______ fuel, food for your body and gasoline for your car. Both 【B2】______ that fuel, first into heat, then energy, some of 【B3】______ is used to do work, and some emitted as waste. And 【B4】______ your car uses more energy when the engine is racing than when it is idling, 【B5】______ does your body use more energy when you are working hard than 【B6】______ you are resting. For the purpose of this comparison, 【B7】______ , there is one significant difference between them. Your car cannot store fuel by turning it into 【B8】______ else all gasoline not 【B9】______ remains as gasoline. But your body stores 【B10】______ energy as fat. When the gas tank is 【B11】______ empty, the car won't run but your body can burn fat to provide more energy. Therefore, if you want to gain weight, you must do 【B12】______ of two things: eat more calories (units of heat, therefore energy), or use less through 【B13】______ . If you want to lose weight, you do the 【B14】______ , decrease your intake of calories or increase the amount of energy you spend. There is 【B15】______ way. Gaining or losing weight is always a relation between intake and output of potential energy. 【B1】______