Hardly a week goes by when the public doesn’t hear coverage of some new nutrition study whose findings seem to contradict previous studies. But what are to make of all this expert yet contradictory advice? Globe Magazine staff writer Neil Swidey decided to delve deeply into the world of nutrition (and its coverage) to understand the forces at work and the degree to which a researcher’s personality intersects with science. Swidey built this journey of explanatory narrative journalism around the fascinating person of Walter Willett, the world’s most-cited nutritionist and one of the most cited scientists in any discipline. A mild-mannered Midwesterner turned Harvard epidemiologist, Willett can be surprising sharp-elbowed when his views are challenged. Despite the fact that Willett is such a giant of medicine, and so often included for a quote in daily news stories on nutrition, he had never been the subject of such an in-depth and penetrating profile.