How to help this person.?

My bf's uncle lives in the house with us and he has always ate way to much. Like binge eating, compulsive eating.... he eats things like karo syrup and brown sugar, just to be eating it. He might only eat once a day but when he does eat its enough for 5 or6 people to live off of all week. I have talked to the doctor about it and they told me they only way they can help him is if he admits he has a eating problem. He wont admit it cause he dont think he has a problem..what can i do to get him help.. and to add this is a 60 year old man. with mental problems.