Like most people, Kimberly Rae Miller does not have the perfect body, but that hasn’t stopped her from trying. And trying. And trying some more. Her first attempt to use food to change her body came at age four, when she learned that the Inuit ate fat to stay warm in the winter. If this diet worked in the Arctic, she reasoned, why not in Long Island? Postcollege, after a brief stint as a diet-pill model, she became a health-and-fitness writer and editor working on celebrities’ bestselling bios—s...