Walter C. Willett, MD, DrPH, has led the Department of Nutrition at the Harvard T.H. Chan School of Public Health for twenty-five years and is Professor of Medicine at Harvard Medical School. A world-renowned researcher, he is a lead investigator of the landmark Nurses’ Health Study and Health Professionals Follow-up Study. Dr. Willett has won many honors, including the Mott Prize, the prestigious award of the General Motors Cancer Research Foundation. Coauthor Patrick J. Skerrett, the former Executive Editor of Harvard Health Publications, is the editor of First Opinion at STATnews.com.