In this episode Julia sits down with neuroscientist and obesity researcher Stephan Guyenet, to talk about what scientists know so far about the causes of obesity, and in particular the brain's role in regulating weight gain. Julia and Stephan cover questions such as: Why did obesity start to increase in the United States in the latter half of the 20th century? Does the body have a "set point" of fat that it tries to defend, and what affects those set points? Are low-carb diets more effective for weight loss than low-fat diets, and if so, what explains the difference?