Responses to overweight and obesity meta-analysis in JAMA (2013)

On Jan 2nd 2013, Flegal, Kit, Orpana and Graubard (from US CDC, University of Ottawa and US NCI) published a systematic review and meta-analysis of the relationship between overweight, obesity and all-cause mortality. This is the story of the initial reaction to that article.

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  1. Our analysis is available at JAMA Forum:
  2. This is not not a complete listing. In particular, a feature of Twitter is 're-tweets': people passing things on to their followers more or less unchanged. These were excluded. Tweets included are examples of larger patterns. Click on the items in the list to see them in their original context.
  3. The paper was published with an Editorial, and the usual press pre-releases

  4. Flegal and colleagues concluded: "Relative to normal weight, obesity (all grades) and grades 2 and 3 obesity were both associated with significantly higher all-cause mortality. Grade 1 obesity was not associated with higher mortality, suggesting that the excess mortality in obesity may predominantly be due to elevated mortality at higher BMI levels. Overweight was associated with significantly lower all-cause mortality."
  5. Heymsfield and Cefalu wrote: "The findings remained consistent even after adjusting for smoking status, preexisting disease, or weight and height reporting method (self or measured)...Body mass index accounts for about two-thirds of the between-individual variation in total adiposity. Body mass index does not account for sex, race, age, and fitness differences in fat mass even at the same body weight. Race and age both influence the associations among disease risk, mortality, and BMI. Moreover, fat distribution varies widely even among individuals at the same level of adiposity, with an abdominal fat pattern conveying the greatest health risks.The NHLBI clinical guidelines recognize this limitation of BMI, and waist circumference is recommended as an additional surrogate marker of the health risks associated with adiposity and adipose tissue distribution.

    Body mass index is known to be an imperfect predictor of metabolic risk. Some individuals with normal BMI have an overweight-obesity metabolic pattern. Others with high BMIs appear to have a healthy metabolic pattern. Factors such as cardiorespiratory fitness are also independent predictors of total mortality in some groups after controlling for BMI, waist circumference, and percentage of body fat. A relatively large fat mass can mask small muscle mass, which is a condition referred to as sarcopenic obesity. Sole use of BMI as a health risk phenotype aggregates people with substantial differences in nutritional status, disability, disease, and mortality risk together into similar BMI categories. Identification of at-risk individuals for overweight and grade 1 obesity is best captured by considering traditional risk factors, including blood pressure, blood lipid levels, and fasting blood glucose level, in addition to BMI, waist circumference, or both...The optimal BMI linked with lowest mortality in patients with chronic disease may be within the overweight and obesity range..."

  6. Early media coverage was measured and included some detailed interpretation from the authors of the original study:

  7. "Still, health experts said that Americans shouldn't treat the new study as a license to eat more.

    "That would be a mistake—and this study did show an increase in mortality for people who are obese," said Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, which conducted the study. "I don't think anyone would disagree with the basic fact that being more physically active and eating a healthier diet is very important for your health."

    The new report is the latest, and largest, to document what scientists call the "obesity paradox."

    Patients should focus more on staying fit and eating healthy than hitting a particular number on the scale.

    "You'd hate to have the message get out there that it's good to be overweight," said Mercedes Carnethon, an epidemiologist at Northwestern University's Feinberg School of Medicine. "The reality is that people who are overweight very often become obese and that's clearly not good."

  8. "We published an article in 2005 that showed, among other things, that overweight was associated with lower mortality — and we got an awful lot of negative feedback from that,” says the current study’s lead author, Katherine Flegal, a senior research scientist at the Centers for Disease Control and Prevention (CDC). Since that  study, however, dozens of others have reached the same conclusion — even if it was hard for researchers and the public to accept.

    “I think there’s a lot of under reporting of this finding […] and so people are sort of repeatedly surprised by it,” Flegal says. Because many researchers don’t expect to find a benefit associated with being overweight, she suggests, they may not believe their results are valid if they find such a connection, which may make them more hesitant to publish them and invite review and discussion about what may be driving the trend.

    Flegal and her co-authors suggest that it’s possible that overweight and obese people get better medical care, either because they show symptoms of disease earlier or because they’re screened more regularly for chronic diseases stemming from their weight, such as diabetes or heart problems. There is also some evidence that heavier people may have better survival during a medical emergencies such as infections or surgery; if you get pneumonia and lose 15 lbs, it helps to have 15 lbs to spare, for example.

    Another possible explanation may involve “reverse causation”: maybe being thin doesn’t make you sick, as some experts argue, but instead being sick can make you thin. Being overweight may be associated with longer lives if people who lose weight because of diseases such as cancer, for example, contribute to earlier death among individuals who weigh less.
    ...the overweight people in the study who tend to live longest may not be fatter than most people at all. Among Americans, at least, they may actually be of average weight.

  9. We wouldn’t want people to think, ‘Well, I can take a pass and gain more weight,’ ” said Dr. George Blackburn, associate director of Harvard Medical School’s nutrition division.

    “Fat per se is not as bad as we thought,” said Dr. Kamyar Kalantar-Zadeh, professor of medicine and public health at the University of California, Irvine.

    “What is bad is a type of fat that is inside your belly,” he said. “Non-belly fat, underneath your skin in your thigh and your butt area — these are not necessarily bad.”

    “Body mass index is an imperfect measure of the risk of mortality,” and factors like blood pressure, cholesterol and blood sugar must be considered, said Dr. Samuel Klein, director of the Center for Human Nutrition at Washington University School of Medicine in St. Louis.

  10. Early Twitter reactions were mixed and sometimes incredulous:

  11. "A pile of rubbish"

  12. On the afternoon of January 2nd (the day that the paper was released in JAMA) Walter Willett from Harvard School of Public Health was interviewed on US National Public Radio. His interview was promoted by the Harvard Media Office and rapidly taken up as a "counter" position to the original study, particularly the soundbite that he provided: that "This study is really a pile of rubbish, and no one should waste their time reading it."