Once every three or four months my son, Sam, grabs a cookie or a piece of candy and, wide-eyed, holds it inches from his mouth, ready to devour it. He knows he’s not allowed to eat these things, but like any 9-year-old, he hopes that somehow, this once, my wife, Evelyn, or I will make an exception. We never make exceptions when it comes to Sam and food, though, which means that when temptation takes hold of Sam and he is denied, things can get pretty hairy. Confronted with a gingerbread house at a friend’s party last December, he went scorched earth, grabbing parts of the structure and smashing it to bits. Reason rarely works. Usually one of us has to pry the food out of his hands. Sometimes he ends up in tears. It’s not just cookies and candy that we forbid Sam to eat. Cake, ice cream, pizza, tortilla chips and soda aren’t allowed, either. Macaroni and cheese used to be his favorite food, but he told Evelyn the other day that he couldn’t remember what it tastes li...