A thoughtful, critical look at how we regard and treat overweight. First, say medical journalist Bennett and science writer Gurin, our images are wrong: what we call fat may not be unhealthy (diabetes and high blood pressure are the only conditions implicated), but our preoccupation with thinness distinctly is. Second: though the reducing diet may be ""our modern ritual of self-improvement and self-purification,"" it's not an effective method of weight control. Bennett and Gurin's interesting proposal (well-supported by the studies they describe) is that a person's body fat content is automatically regulated, and is a biological fact of life: since a body is ""uncomfortable"" at another level, staying on a reducing diet for any length of time is extremely difficult. Some control system in the body, they suggest, determines a ""setpoint"" for body fat content; the only lasting method of lowering the setpoint (as research by Jean Mayer, and others, has indicated) is through exercise--which alters the body's physiology. The other major discussion: how ""fat people suffer because they live in a culture that derides their bodies, encourages them to starve themselves, and declares that character flaws have made them fat."" In that connection, Bennett and Gurin take an interesting look at art, fashion, the women's movement, and politics. They toss in lots of studies--classic and offbeat--to back up their ideas; take apart the most recent fad diets (also, the behavioral techniques for reducing food intake--which, they say, resemble the behavioral disorders found in anorexics); and make their case with humor (""How to Write Your Own Diet Book"" in ten steps--the last two being ""Blame the victim"" and ""Cover yourself""). Many readers will want to agree with this fresh, knowledgeable appraisal--and specialists can learn a few things too.