What is a risk of having too little body fat

Well... A complicated risk has to do with your metabolism. Under most normal circumstances your body will use glucose and oxygen to make energy. When however you don't have the glucose your body is able to use fat for energy. However if there is to little fat and your body needs energy than you run the risk your body metabolizing your muscles. Of course this is dangerous and quite unpleasant, but an even more dangerous complication is the acid waste that results which can cause acidosis.