Rethinking Thin: The New Science of Weight Loss—and the Myths and Realities of Dieting, by Gina Kolata, New York: Farrar, Straus, and Giroux, 257 pages, $24 Mindless Eating: Why We Eat More Than We Think, by Brian Wansink, New York: Bantam Books, 276 pages, $25 Gina Kolata says losing weight is nearly impossible. Brian Wansink says it’s easy. But they don’t really contradict each other, because they’re talking about different kinds of weight loss.Although their new books offer very different messages for dieters, Kolata and Wansink share a suspicion of collectivist responses to the “obesity epidemic.†Both writers are intensely...