Humans love to eat and drink. As they grow older, their body systems slow down little by little. When metabolism slows down, the process of breaking down everything that is put into the body takes longer. If carbohydrates and fats are not broken down fast enough, then they are stored for future use. Weight is gained when energy is not burned off as fast as it is being put in. People really concerned about this will turn to fad diets or use a Metabolism Booster to burn off the excess energy units faster.