Athletes and dancers need more than artists and writers who do not move around as much. Sometimes we aren't happy with the way we look. Some people want to be skinny, some people want to be fatter. Skinny people might eat lots of food, fat people may eat very little, but still they stay just the same. This is because different people have a different meatbolism.
Metabolism depends on how a person changes food to fat, and how the body stores the fat.
People with a high metabolism turn the fat into energy at a much higher rate, the food is used up quickly. Others have a slow metabolism and use it slowly, storing the fat in their body. This is just the type of body that they have. A fat person might think that by not eating they will become skinny. But the rate of metabolism doesn't depend on the amount of food eaten.