While reading it I got the feeling the joy comes from not depriving yourself of food. They think normal weight people are miserable because we don't allow ourselves to give in to unbridled gluttony. Happiness to fats is a gallon of ice cream, a pan of brownies and some whipped cream whereas some of us would prefer a hike. They have deluded themselves into thinking everyone lives for food and if we don't we're just kidding ourselves.