As a young surgeon, Peter Attia felt contempt for a patient with diabetes. She was overweight, he thought, and thus responsible for the fact that she needed a foot amputation. But years later, Attia received an unpleasant medical surprise that led him to wonder: is our understanding of diabetes right? Could the precursors to diabetes cause obesity, and not the other way around? A look at how assumptions may be leading us to wage the wrong medical war.