In this week's episode we discuss two decades of nutrition science with one of the leading experts in the field. Walter Willett, former chair of the Department of Nutrition, recently released an updated version of his book Eat, Drink, and Be Healthy , which compiles decades worth of evidence about the components of a healthy diet. During an in-depth conversation with Willett, we talk about what's changed in nutrition since the book was first released in 2000 and the topics that will dominate the field in the years to come—including obesity—and how climate change will force us to change how we eat.