If you ask any doctor out there they will tell you that extreme weight loss is safe only if it is done the right way. The key to losing weight is to do it in a smart way where you are not trying to "shock" the body, but instead naturally lose the weight. You dont want to lose 100 pounds in six months unless you are doing it under a supervised regime. This is why simply starving yourself is never the right way to go. If you are looking to lose weight quickly, you want to make sure that you have a well thought out plan in mind.