About
Dr. William N. Duffy has practiced internal medicine in the Philadelphia area for over 30 years. He earned his Bachelor of Science magna cum laude from Seton Hall University, then his medical degree from Georgetown University School of Medicine. He completed his residency in Internal Medicine at Thomas Jefferson University Hospital, where the program later honored him as teaching attending of the year in 2001.
In 2002, Dr. Duffy joined the University of Pennsylvania Health System and spent more than two decades there. He serves as an associate professor of clinical medicine at the Perelman School of Medicine. He co-founded the Culinary Medicine program at Perelman and contributes to its Culinary Medicine Leadership Board. He holds board certification in Internal Medicine and certification as a personal trainer through the National Academy of Sports Medicine. He previously served as team physician for both the Philadelphia Flyers and the Philadelphia Eagles. Castle Connolly has recognized him as a Top Doctor for over a decade. Dr. Duffy is passionate about food as medicine, plant-based nutrition, and the role of lifestyle in preventing and treating disease.
Education & Training
Undergraduate
Seton Hall University, Bachelor of Science (magna cum laude)
Medical School
Georgetown University School of Medicine
Residency
Internal Medicine, Thomas Jefferson University Hospital
Additional Training
Associate Professor of Clinical Medicine, Perelman School of Medicine; Certified Personal Trainer, National Academy of Sports Medicine
Certifications
Conditions Treated
Who is Dr. Duffy right for?
Dr. Duffy is an excellent fit for adults seeking a preventive and lifestyle-centered approach to internal medicine. Patients managing chronic conditions through nutrition and exercise will find his background especially relevant. Executives and professionals looking for a physician with deep academic credentials and regional specialist connections benefit from his network. Anyone interested in plant-based nutrition or food as medicine will connect with his clinical philosophy. His panel of 50 families allows him to provide thorough, unhurried care.
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Frequently Asked Questions
Dr. Duffy specializes in internal medicine, preventive medicine, and functional medicine. He brings a particular focus on lifestyle, plant-based nutrition, and culinary medicine as tools for preventing and treating disease. He co-founded the Culinary Medicine program at the Perelman School of Medicine and teaches there as an associate professor.
Yes, Dr. Duffy holds board certification in Internal Medicine. He also carries certification as a personal trainer through the National Academy of Sports Medicine, reflecting his commitment to fitness and lifestyle as core components of health.
Dr. Duffy earned his medical degree from Georgetown University School of Medicine. He completed his residency in Internal Medicine at Thomas Jefferson University Hospital, where he later received the teaching attending of the year honor in 2001.
Dr. Duffy has practiced internal medicine in the Philadelphia area for over 30 years. He spent more than two decades within the University of Pennsylvania Health System before co-founding MD² Philadelphia in 2025.
Yes, Dr. Duffy previously served as team physician for both the Philadelphia Flyers and the Philadelphia Eagles. That experience reflects his long-standing interest in physical performance, fitness, and proactive health management.
Castle Connolly has recognized Dr. Duffy as a Top Doctor for over a decade. This recognition reflects his standing among peers in the Philadelphia medical community.
Dr. Duffy is passionate about food as medicine and plant-based nutrition. He co-founded the Culinary Medicine program at the Perelman School of Medicine and co-directs a culinary medicine course there. He integrates nutritional counseling directly into his clinical care.
Dr. Duffy sees adults seeking comprehensive internal medicine care with a strong preventive focus. He works well with patients managing chronic conditions, those interested in lifestyle-based treatment, and individuals who want a physician deeply engaged in their long-term health.
Doctor profile last updated March 21, 2026