His studies found that the weights of adoptees showed a far greater resemblance to the weights of their biological parents than to adoptive parents. The work foreshadowed findings that genes explain much of the variation in human body weight.
"Dr. Stunkard really is the dean of obesity research," Tom Wadden, director of Penn's Center for Weight and Eating Disorders, said in a 2007 interview.
Dr. Stunkard was born in 1922 in New York City and studied at Yale University before earning his medical degree in 1945 from Columbia University's College of Physicians and Surgeons. He served two years as an Army physician, principally in Japan, where he began a lifelong interest in Buddhism and meditation, his wife said.
He worked for four years at Cornell Medical College in New York before joining Penn's Psychiatry Department in 1957. He was appointed chairman in 1962. He was recruited to Stanford University in 1973 to chair the psychiatry department, but returned to Penn in 1977.
Dr. Stunkard's work on obesity began in 1955 with research into night-eating syndrome, a topic to which he returned at the end of his career.
He surveyed obesity treatment studies in the late '50s and found that the nation's diet programs could claim only a 2 percent success rate. He was an early advocate for the use of bariatric surgery to induce weight loss. He also published the first modern account of binge eating in obese individuals.
Dr. Stunkard's work was funded continuously for five decades by the National Institutes of Health. He was elected to membership in the Institute of Medicine of the National Academy of Sciences, among numerous professional associations.
He received many awards, including the 1994 Distinguished Service Award from the American Psychiatric Association and the 2004 Sarnat International Prize from the Institute of Medicine.
In addition to his wife, he is survived by a stepdaughter, Elana Maurin; her husband, Keith Renshaw; and their two children.
Burial is private. A memorial service will be held in the fall at Penn.
The family requests that, in lieu of flowers, expressions of sympathy be directed to Doctors Without Borders, 333 7th Ave., New York, NY 10001, or the Council for a Livable World, 322 4th St. NE, Washington, DC 20002.