Another clear, compelling brief for exercise and fitness as the way to weight loss and better health--with some knowledgeable how-to advice and a smart rap at weight-loss obsession. Basically, Mirkin (The Sportsmedicine Book, CBS Radio) suggests using self-perception of well-being, rather than weight, as a guide to whether reducing or a stepped-up fitness program is called for. (Don't get hung up on society's adoration of the super-skinny.) Recent studies, he notes, have found that ""being fat makes your body behave differently, in ways that tend to keep you fat""; implicated are the body's metabolic set-point (how rapidly it burns fat), hormonal interactions, and other, more exotic possibilities (brown vs. yellow fat, a so-called sodium pump). As regards diet, Mirkin discusses daily requirements and recommends a 1300-calorie regimen (higher than usual, but his minimum to ensure proper nutrient intake). On exercise (the source, for Mirkin, of weight loss), he goes into detail on how to pick an activity that's fun, that gives cardiovascular benefits, and that uses lots of energy. (Kissing with Rhett-Butler gusto takes twelve calories; ""otherwise, it's only about a six-calories happening."" Sex may use up to 250.) Gutin (The High-Energy Factor), Kuntzleman (Diet Free), and Katahn (The 200 Calorie Solution) have covered almost the same ground; Mirkin adds some new, supportive research findings and a timely accept-your-weight pitch.