A century ago, Elsie Scheel was the perfect woman. So said a 1912 article in The New York Times about how Miss Scheel, 24, was chosen by the “medical examiner of the 400 ‘co-eds’ ” at Cornell University as a woman “whose very presence bespeaks perfect health.”

Miss Scheel, however, was hardly model-thin. At 5-foot-7 and 171 pounds, she would, by today’s medical standards, be clearly overweight. (Her body mass index was 27; 25 to 29.9 is overweight.)

But a new report suggests that Miss Scheel may have been onto something. The report on nearly three million people found that those whose B.M.I. ranked them as overweight had less risk of dying than people of normal weight. And while obese people had a greater mortality risk over all, those at the lowest obesity level (B.M.I. of 30 to 34.9) were not more likely to die than normal-weight people.

The report, although not the first to suggest this relationship between B.M.I. and mortality, is by far the largest and most carefully done, analyzing nearly 100 studies, experts said.