Researchers from the Boston University School of Public Health and the Harvard T.H Chan School of Public Health sought to investigate the relationship between maximum BMI (body mass index) over time and subsequent mortality. The researchers assessed maximum BMI for more than 225,000 participants across 16 years of weight history in three large prospective studies and then examined deaths that occurred within an average of 12 years of follow-up. The analysis found that people with a maximum BMI in the overweight or obese categories were at elevated risk for all-cause death, as well as death from cardiovascular disease, cancer and respiratory disease. The highest risk for death occurred among participants who had significant drops in weight, which the authors said most likely reflected unintentional weight loss caused by illness.
The authors say that these findings are important from a public health perspective, given that about one-third of adults in the U.S. and more than a quarter of the world’s population is overweight. This is more reason why people should follow a healthy lifestyle and try to keep a normal weight.
The study made no exclusions based on a history of smoking or illness, and the pattern of excess risk with a maximum BMI above normal weight held for all ages, regardless of sex. Prior studies contesting the obesity paradox have been criticized by some researchers for restricting their samples to small percentages of the total in an effort to reduce biases related to lower weight that results from chronic diseases or smoking. The researchers noted that most participants were white and highly educated, so the results may not apply to more diverse populations.