Gary Taubes, author of Why We Get Fat, talks with EconTalk host Russ Roberts about why we get fat and the nature of evidence in a complex system. The current mainstream view is that we get fat because we eat too much and don't exercise enough. Taubes challenges this seemingly uncontroversial argument with a number of empirical observations, arguing instead that excessive carbohydrate consumption causes obesity. In this conversation he explains how your body reacts to carbohydrates and explains why the mainstream argument of "calories in/calories out" is inadequate for explaining obesity. He also discusses the history of the idea of carbohydrates' importance tracing it back to German and Austrian nutritionists whose work was ignored after WWII. Roberts ties the discussion to other emergent, complex phenomena such as the economy. The conversation closes with a discussion of the risks of confirmation bias and cherry-picking data to suit one's pet hypotheses.