Last month, JAMA published a systematic review and meta-analysis of the relationship between body mass index (BMI) and all-cause mortality. The researchers, led by Katherine M. Flegal, PhD, of the US Centers for Disease Control and Prevention, found that people who are categorized as being mildly obese according to their BMI had no increased risk of dying prematurely, and overweight people a slightly reduced risk of dying prematurely, compared with their normal-weight counterparts-a finding supported by previous studies. In an accompanying editorial, 2 researchers said that the findings highlighted the limitations of increased BMI as an indicator of unhealthiness. Early coverage of the study in the mass media was restrained, emphasizing the authors' main messages. Response in social media such as Twitter ranged from excited acceptance to confusion and voicing of familiar critiques, such as the limitations of observational studies or of using all-cause mortality as an outcome measure rather than morbidity or disability. And then the response evolved and became heated.