Researchers from the Boston University School of Public Health (BUSPH) and the University of Pennsylvania recently reported that existing studies linking obesity and mortality have not considered the long-term effects of continuous weight loss or change, and that one-time measures of body mass index (BMI) are not enough.
The study was published in the journal Proceedings of the National Academy of Sciences, titled “Revealing the burden of obesity using weight histories.”
“The risks of obesity are obscured in prior research because most of the studies only incorporate information on weight at a single point in time,” Dr. Andrew Stokes, the study’s lead author and assistant professor of global health at BUSPH, said in a news release. “The simple step of incorporating weight history clarifies the risks of obesity and shows that they are much higher than appreciated.”
The study claims that most research on obesity has neglected the impact of excess weight on mortality. For example, studies that do not distinguish between people who have never been overweight and people of normal weight who were formerly overweight or obese are inaccurate because they do not take into account the enduring effects of former obesity, and also disregard the fact that weight loss is commonly linked to disease.
Stokes and the study’s co-author, Dr. Samuel Preston, a sociology professor at Penn, analyzed models to gauge obesity status through reports of the participants’ lifetime maximum weight instead of a momentary survey.
Researchers used the comprehensive 1988-2010 National Health and Nutrition Examination Survey, crossing it with death certificate records in 2011, and employed statistical criteria to compare the performance of various models. Participants were asked to note their maximum lifetime weight as well as their weight at the time of the survey.
Researchers found that 39 percent of all normal-weight participants had previously belonged to higher-weight categories. Furthermore, the team found more reports of cardiovascular disease and diabetes among people who had reached a higher-than-normal BMI and then lost weight, compared to people who remained in the same category, and that people with normal weight at the time of treatment but with greater weight variations scored 27 percent higher death rates than those who had never exceeded their current weight category.
The authors concluded that models using data on lifetime maximum weight outperformed those with single data on weight at the time of the survey in predicting mortality. For Stokes and Preston, using “weight stories” in obesity and mortality studies is crucial because first, obesity at a particular age may predispose people to illness, regardless of weight loss further on, and second, weight loss is often caused by illness.
“The disparity in predictive power between these models is related to exceptionally high mortality among those who have lost weight, with the normal-weight category being particularly susceptible to distortions arising from weight loss,” said the authors. “These distortions make overweight and obesity appear less harmful by obscuring the benefits of remaining never obese.”
The theme is controversial, with some past studies showing that losing weight when overweight may lead to higher death rates. Part of the reason for this is that illness may be the main contributing factor for that weight loss due to a loss of appetite or higher metabolic demands. Some studies also suggested that excess weight may be a protective factor in health, like one particular study in 2013 that indicated that being overweight was associated with lower mortality, and minor obesity was reported to be not dangerous to people’s lives.
Stokes and Preston urged more research based on this “weight stories” methodology, including studies focused on smoking, where current smokers are distinguished from former smokers and those who never smoked.
