American eaters love a good villain. Diets that focus on one clear bad guy have gotten traction even as the bad guy has changed: fat, carbohydrates, animal products, cooked food, gluten. And now Robert Lustig, a pediatric endocrinologist at the University of California at San Francisco, is adding sugar to the list. His book "Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease" makes the case that sugar is almost single-handedly responsible for Americans' excess weight and the illnesses that go with it. "Sugar is the biggest perpetrator of our current health crisis," says Lustig, blaming it...