Late in the morning on 20 February, more than 200 people packed an auditorium at the Harvard School of Public Health in Boston, Massachusetts. The purpose of the event, according to its organizers, was to explain why a new study about weight and death was absolutely wrong. The report, a meta-analysis of 97 studies including 2.88 million people, had been released on 2 January in the Journal of the American Medical Association (JAMA)1. A team led by Katherine Flegal, an epidemiologist at the National Center for Health Statistics in Hyattsville, Maryland, reported that people deemed 'overweight' by international standards were 6% less likely to die than were those of 'normal' weight over the same time period. The result seemed to counter decades of advice to avoid even modest weight gain, provoking coverage in most major news outlets — and a hostile backlash from some public-health experts. “This study is really a pile of rubbish, and no one should waste their time reading it,” said Walter Willett, a leading nutrition and epidemiology researcher at the Harvard school, in a radio interview. Willett later organized the Harvard symposium — where speakers lined up to critique Flegal's study — to counteract that coverage and highlight what he and his colleagues saw as problems with the paper. “The Flegal paper was so flawed, so misleading and so confusing to so many people, we thought it really would be important to dig down more deeply,” Willett says.
But many researchers accept Flegal's results and see them as just the latest report illustrating what is known as the obesity paradox. Being overweight increases a person's risk of diabetes, heart disease, cancer and many other chronic illnesses. But these studies suggest that for some people — particularly those who are middle-aged or older, or already sick — a bit of extra weight is not particularly harmful, and may even be helpful. (Being so overweight as to be classed obese, however, is almost always associated with poor health outcomes.)