Does being overweight really reduce mortality? No wonder the public is confused

Expert discussion at HSPH on the controversial JAMA article which claimed that being overweight leads to reduced mortality.

Click here to view the video webcast presented by the Department of Nutrition at Harvard School of Public Health: Does being overweight really reduce mortality?

Harvard School of Public Health’s Department of Nutrition assembled a panel of health experts to elucidate inaccuracies in a recent high-profile JAMA article whichScale_tape claimed that being overweight leads to reduced mortality. In his opening remarks, HSPH Dean of Faculty Julio Frenk called for a deeper discussion of this matter given the conflicting reports on a topic of such fundamental importance to Americans’ health. Each panelist presented a clear, compelling case as to why the general public should not rely on these flawed study findings, giving attendees numerous reasons to question the validity of the study.

Moderated by Dr. Jeffrey Flier, Dean of the Faculty of Medicine and Caroline Shields Walker Professor of Medicine at Harvard Medical School, panelists included:

Katherine M. Flegal, PhD (invited; not in attendance)
Epidemiologist, National Center for Health Statistics, Centers for Disease Control and Prevention

JoAnn E. Manson, MD, DrPH
Chief, Division of Preventive Medicine, Brigham and Women’s Hospital, and Professor of Medicine and the Michael and Lee Bell Professor of Women’s Health, Harvard Medical School, and Professor, Epidemiology, Harvard School of Public Health

Michael Thun, MD, MS
Vice President Emeritus, Surveillance and Epidemiology Research, American Cancer Society, Inc.

Frank Hu, MD, PhD
Professor of Nutrition and Epidemiology, HSPH, and Professor of Medicine, Harvard Medical School, Director, Harvard Transdisciplinary Research in Energetics and Cancer Center (TREC), Director, Boston Nutrition and Obesity Research Center (BNORC) Epidemiology and Genetics Core

Steven Heymsfield, MD
George A. Bray, Jr. Endowed Super Chair in Nutrition, and Executive Director, Pennington Biomedical Research Center

Walter Willett, MD, DrPH
Fredrick John Stare Professor of Epidemiology and Nutrition, and Chair of the Department of Nutrition, HSPH, and Professor of Medicine, Harvard Medical School

While each panelist presented strong evidence of flaws in the Flegal et al. study, Dr. Frank Hu summed up the two main reasons for the reported inverse association between overweight and mortality.  As Dr. Hu explained, this perceived inverse relationship was in large part because the analysis combined smokers, as well as sick and elderly people, without separate data for younger individuals (<65 years old).  As summarized by Dr. Walter Willett in a recent interview:

The most serious problem in the Flegal paper is that their normal weight group included a mix of lean and active people, heavy smokers, patients with cancer or other conditions that cause weight loss, and frail elderly people who had lost weight due to rapidly declining health. Because the overweight and obese groups were compared to this mix of healthy and ill persons who have a very high risk of death, this led to the false conclusions that being overweight is beneficial, and that grade 1 obesity carries no extra risk. Also, because the Flegal study did not use the original data from the published papers, they could not look separately at different age groups, and we know that the relation between body weight and mortality is much stronger before age 65 than at older ages.

Dr. Hu also highlighted another crucial weakness in the study design, which is that many high-quality studies (including approximately 6 million people) were excluded from the primary analysis because they did not use standard BMI categories in the analysis. Because of this flawed methodological approach, Dr. Hu explained, the JAMA article lacks validity and these study findings cannot be generalized to anyone. Dr. Willett added that the misleading data sends an erroneous message to the public as well as health care practitioners, and undermines the credibility of science, policy and public health efforts to address obesity.

In his closing remarks, Dean Frenk reminded us that we live in an era where access to information is ubiquitous, and that science data is now part of the general culture. In creating a social environment that fosters knowledge, he said we also need to implement “necessary safeguards” to promote credible science and minimize confusion.

Read more about this panel discussion at:

Harvard School of Public Health

Harvard Medical School

Harvard Gazette