Six years ago, Mark Bittman was a full-time omnivore. But then a doctor told him to turn vegan for health reasons, and suddenly Mark found himself facing a world void of meat, dairy, or processed foods. So the New York Times food writer decided to personalize his vegan diet and allow for some cheating. He called it "Vegan Before 6," or "VB6," and says it helped him improve his health and focus on cooking at home. Mark Bittman talks about his new book, and how a full-time meat lover adapted to part-time veganism.