short version when a body is deprived of what it needs it goes into survival mode. it starts storing everything that it takes in as fat cells, the body also survives by gathering what it needs from bone, muscles organs. the result sometimes the person ...looks.....skinnier because bone mass, organs, muscle mass is being affected but can weight in more because whats being taken in is stored and reserved for later.

suggestion rather than starving yourself by limiting what you are taking in consult with your medical doctor (or one in your location) they can help you develop a diet\exercise plan that will not only allow you to restrict your calories, lose weight and not affect your vital organs, bones and muscles.