According to several accounts, many of which are from the Kingpin himself, his total body fat is as low as 2%. This suggests that muscle accounts for 98 percent of his overall weight. That is how he is able to be as powerful as he is, even against super-powered opponents. Even if they don't have such low body fat percentage. It also means that he needs to eat about 2,500 calories per day in order to not lose weight. His body also produces a protein called myostatin, which is responsible for regulating muscle growth and development. His body is also known to produce a hormone called IGF-1, which helps repair tissue and grows new cells. All these factors together make up why the Kingpin is one of the most powerful villains in comics.