One more time: a sound, if unexciting, explanation of why and how to lose weight by eating properly and exercising more. In Part I, biochemists Van Orden and Steed describe, in reasonably clear detail, the chemical and biological laws that govern the body; why some people are fat (food-intake controls, metabolic controls); how the body uses food; how behavior modification can affect these processes; and how fad diets give the illusion of successful weight loss. The conclusion, of course, is that the only way to lose weight is to eat less and exercise more--so Part II offers instructions, reference tables, and recording forms that readers can use to construct their own weight-control programs, both for loss and maintenance (1000-1500 calories, use of food exchanges, and exercise of gradually increasing difficulty beginning with a walking program). Part III then provides brief advice on how those with special needs--adolescents, pregnant women--can adapt the program accordingly. Reliable, though routine.