Researchers predict nearly half of Americans will be obese by 2035. What to know.

Adult obesity in the United States has gone up over the past 30 years and more increases are expected in the next decade, according to a new study.

In the study, published Tuesday, Jan. 28, in JAMA, researchers found 19.3% of U.S. adults were living with obesity in 1990, which increased to 42.5% by 2022. The researchers also forecast the number will increase to 46.9% by 2035.

Using two cross-sectional, nationally representative surveys, the study analyzed data from a total of 11,315,421 U.S. participants.

Registered dietitian Ashley Koff, who was not involved in the study, told USA TODAY it's not surprising to see that these numbers have increased for a multitude of factors.

But she also said the way the study defined obesity using BMI, a measurement based on height and weight, is problematic. Other health experts have also criticized the method as outdated.

"These numbers actually don’t tell us about the health of individuals or anything about the mental health, the frustration or the dollar amount that people have invested in trying to optimize their overall health and doing so to lose weight," she said.

The authors noted this limitation, writing BMI does "not directly measure body fat or account for body composition," adding these errors "may differ by demographic group." Other limitations included sparse data in some locations and self-reported health information.

When looking at variations in age, sex, race and ethnicity groups, there were large disparities in obesity prevalence.

For example, the largest increases were among Hispanic females and males while the smallest increases were among non-Hispanic Black males.

In 2022, non-Hispanic Black females had the highest obesity prevalence at 56.9% while Hispanic males,non-Hispanic White males and females, and non-Hispanic Black males had similar prevalence, ranging from 40.1% to 42.6%.

The results also showed increases in obesity among younger ages over the past several decades, representing earlier onset of obesity.

Obesity varied by state, too. In 2022, white males and females had similar numbers, with prevalence lowest in the District of Columbia and highest in West Virginia. For the Hispanic population, this differed, with obesity generally highest in the Midwest and the South − specifically Oklahoma for females and Indiana for males.

The authors note these disparities are likely the result of several factors, including race-based discrimination, food insecurity and differing access to healthy food and space for physical activity.

"Physical inactivity and or diet do not exist in isolation, often reflecting deep socioeconomic disparities and representing only some of the many causes of obesity that policy interventions can target to blunt its concerning trajectory," the authors wrote.

Koff added that, while it's great people are talking more about nutrition now, access to support is limited.

"We need to have access to people that can help prevent this as we go along the path by personalizing plans and helping implement those plans, which is what qualified dietitians and coaches would be doing," she said. "Currently that is not accessible via insurance or to most, even with a diagnosis of obesity and diabetes."