Daily twelve-hour fasting introduces a period of very low insulin levels during the day. This prevents the development of insulin resistance, making the twelve-hour fast a powerful preventative weapon against obesity. In fact, the combination of whole foods, lower-carbohydrate diets, less added sugars, and a daily twelve-hour fast was enough to prevent most Americans in the 1950s and 1960s from developing obesity—even though they still ate plenty of white bread and jam, and whole-wheat bread was rare and whole-wheat pasta
