What makes us fat

Everyone knows that we will become fat, if we eat too much and do less exercise. However, we will gain weight even when we are doing exercise. What is the killer that leads to fat?
In hot summer, we will enjoy coolness if we stay at the room equipped with an air conditioner. There will be less heat consumed when people enjoy the comforts brought by air conditioner. The chances of putting on weight will be more possible when people begin to work. We are busy working and have less time to do sports, so it is easier to gain weight. Sometimes, the result will go into the opposite direction with your willing, if you excessively force yourself to lose weight. You should remember that you can gain the better result with a nice mood. Have you ever thought that lunch has much to do with being fat? Fast food is rich in heat, which you can't imagine. In fact, undersleep will also make you gain weight.
If you want to keep thin, you should keep you away from the factors mentioned above.