Overweight, according to these experts from a weight-loss clinic at the University of Pennsylvania, is the result of poor snacking habits, guilt, and the distorted view that overeating is somehow related to moral weakness (a fat person eats a slice of cake, feels guilty, and has a second slice to boost his spirits). No good, say the authors, who provide some simple, behavior-control tricks to change those habits so that a fatty can metamorphose into a skinny. They claim that if you eat slowly your natural repletion mechanism will function, and you'll stop when you're really full--not just when you think you are. Moreover, if you chart your food intake, as well as where you're eating the stuff and how often, you can avoid problem places and times of day. In other words, if you crave ice cream, eat it. But not very much, and then only when you've ""banked"" the extra calories by not eating, say, dessert at dinner. Eat 10 calories a day for each pound you weigh to maintain your weight. To lose, eliminate 3,500 calories each week. A gentle program, this, and one designed to get weight off slowly so that it stays off. For the ravenous audience with a diet book in one hand, and a pizza in the other.