Half of population projected to have obesity by 2030, Harvard study says

About half of the adult U.S. population will have obesity and about a quarter will have severe obesity by 2030, according to a new study led by Harvard T.H. Chan School of Public Health in Boston, Massachusetts and published in the New England Journal of Medicine.

The study also predicts that in 29 states, more than half of the population will have obesity, and all states will have a prevalence of obesity higher than 35 percent. The study's researchers estimate that, currently, 40 percent of American adults have obesity and 18 percent have severe obesity.

The researchers said the predictions are troubling because the health and economic effects of obesity and severe obesity take a toll on several aspects of society.

 "Obesity, and especially severe obesity, are associated with increased rates of chronic disease and medical spending, and have negative consequences for life expectancy," said Steven Gortmaker, PhD, senior author of the study and professor of the practice of health sociology, in a statement.

For the study, the researchers used self-reported body mass index (BMI) data from more than 6.2 million adults who participated in the Behavioral Risk Factor Surveillance System Survey (BRFSS) between 1993 and 2016. BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters. Obesity is defined as a BMI of 30 or higher, and severe obesity is a BMI of 35 or higher.

Self-reported BMIs are frequently biased, so the researchers used novel statistical methods to correct for this bias. The large amount of data collected in the BRFSS allowed the researchers to drill down for obesity rates for specific states, income levels, and subpopulations.

The results showed that by 2030, several states will have obesity prevalence close to 60 percent, while the lowest states will be approaching 40 percent. The researchers predicted that nationally, severe obesity will likely be the most common BMI category for women, non-Hispanic black adults, and those with annual incomes below $50,000 per year.

Researchers said the study could help inform state policy makers. For example, previous research suggests that sugar-sweetened beverage taxes have been an effective and cost-effective intervention for curtailing the rise in obesity rates.