As obesity escalates, the diet business is booming. In this three-part series, Jacques Peretti investigates the connections between obesity and weight loss, and confronts some of the businesses making a fortune from consumerists' desire to become thin, including a conversation with a former director of Weight Watchers. Peretti examines the scientific reasons why so many diets fail long term and why — in spite of this failure — people tend to go back to them again and again.