They have to watch what they eat in case they have too much sugar, starch or fat. Which causes them have to avoid all white foods. This is to control their blood glucose level. If their blood sugar gets to high they will have to take insulin through almost like a shot but not really, so that their blood sugar goes down. If it gets too high then they could eat/drink things that would bump their blood sugar back up to normal levels ( things like orange juice, pop-tarts, Fruit Roll Ups etc.)