Nearly half of all adults in the US will be obese just 10 years from now, according to new projections published in the New England Journal of Medicine. Nearly a quarter will be severely obese.

Currently, about 40 percent of US adults are obese and about 20 percent are severely obese.

The new modeling study, led by public health researchers at Harvard, attempts to provide the most accurate projections yet for the country’s obesity epidemic, which is increasing at a concerning rate. “Especially worrisome,” the researchers write, “is the projected rise in the prevalence of severe obesity, which is associated with even higher mortality and morbidity and health care costs” than obesity.

For the study, the researchers defined weight categories by body mass index, BMI, defined as the weight in kilograms divided by the square of the height in meters. BMI’s of under 25 were considered underweight or normal weight, 25 to 30 were considered overweight (25 to <30), 30 to 35 were considered moderate obesity, and 35 or over were considered severe obesity.

To model the projections, the researchers drew from 20 years’ worth of data on a nationally representative sampling of more than six million people.

But unlike previous projections that attempted to predict the trajectory of the obesity epidemic, the new analysis tried to compensate for a weakness in the data gathered—that is, that the weight information was mainly collected in a nationwide telephone survey, and people have a general tendency to under-report their actual weight.

To get a more realistic picture of Americans’ weight and where it's headed, the researchers essentially adjusted the biased survey data to better match the weight distribution seen in another study where weight and body measurements were collected in a standardized exam procedure. That study was smaller—involving just over 57,000 adults—but was still national-representative.

The researchers then used the adjusted date to model projections. While the overall picture is not good, projections for certain demographics and states were particularly concerning. For instance, Alabama, Arkansas, Oklahoma, and West Virginia have projected obesity rates nearing 60 percent 10 years from now. And by 2030, severe obesity will be the most common BMI category nationwide among women, black non-Hispanic adults, and adults in low-income households (less than $50,000), the researchers report.

Overall, severe obesity will be more common in 2030 than obesity was in the 1990s.

The data is a signal that doctors need to be better at addressing and treating obesity, which carries a slew of health risks. Those include an increased risk of type II diabetes, stroke, coronary heart disease, osteoarthritis, some cancers, as well as all-cause mortality.

“In addition to the profound health effects,” the researchers write, "…the effect of weight stigma may have far-reaching implications for socioeconomic disparities as severe obesity becomes the most common BMI category among low-income adults in nearly every state."

Given how difficult it can be to lose weight, the researchers say more emphasis should be placed on preventing weight gain to begin with.

NEJM, 2019. DOI: 10.1056/NEJMsa1909301 (About DOIs).