my dad's test results indicated he's acquired diabetese, so what should he eat??

I suggest watching his diet and exercise. Diabetes can be controlled in these 2 ways. The docter should of given him a diabetic diet to follow. (ADA diet) That is very helpful in knowing what to eat and what to stay away from. If I were you, research diabetes to become more aware of the disease. Maybe walk with your dad daily. This will give you a better bond with your father and improve his health as well as yours.