Well, a donut isn't that bad for you. However, as food goes they definitely are not the best. They are typically made with a lot of sugar, chocolate, and other toppings, the flour used is highly refined, there is a lot of fat often in the dough itself depending on the type, and then it is deep fried. So take your pick as the top reason they are so bad for you... My favorite of course is: You usually eat too many.