Obesity science has reached a crossroads: The carbohydrate hypothesis is poised to overtake "calories in, calories out" as the predominant understanding of weight gain. Physicians, dietitians and trainers have come to treat "carbs are bad" as a new gospel, preaching a lifestyle that strays very far from the true scientific consensus. In "What Is Fat For?" Ignatius Brady, a weight loss physician and science writer, presents a fresh perspective on obesity...