My 2 year old black labrador not eating?

OK,we have a 2 YEAR OLD BLACK LABRADOR.He stays at home and is lazy.Rarely goes out for walk with me.And the thing that's worrying me the most is that he is not eating.We have good quality dog food.But,he aint eating.He only fried chicken that we bring KFC.He doesnt eat anything else.I am worried coz I think he has some problem with his metabolism somethng.I am going to take him to vet next week.But,I wanna know if anyone else has faced this problem and if yes,what was the real problem and how did you solve it?