Obesity in the U.S. is at a high level and has remained stable, but the proportion of people with severe obesity — particularly women — has increased compared with a decade ago, according to new government research.

According to a survey of about 6,000 people in 2021-2023, the obesity rate in the US is around 40%. The US Centers for Disease Control and Prevention found that about 1 in 10 people surveyed had severe obesity.

Women were almost twice as likely as men to be severely obese.

Overall obesity rates appeared to have decreased compared to the 2017-2020 survey, but this change was not considered statistically significant; the numbers are so small that it is mathematically likely that they have not actually decreased.

That means it’s too early to know whether new treatments for obesity, including blockbuster weight-loss drugs such as Wegovy and Zepbound, can help reduce the chronic disease epidemic linked to a host of health problems, said Dr. Samuel Emrich, a CDC public health official who led the latest study.

“We can’t look at prescription drug use in great detail and compare it to changes in obesity prevalence,” Emrich said. “Hopefully, that’s something we’ll be able to look at in the future.”

Most importantly, however, the overall obesity rate in the U.S. has not changed much in a decade, while the rate of severe obesity has risen from about 8% in the 2013-2014 survey to nearly 10% in the most recent survey. Prior to this, obesity in the U.S. had risen sharply since the 1990s, federal surveys have shown.

Measurements of obesity and severe obesity are determined according to the body mass index, which is a calculation based on height and weight. People with a BMI of 30 are considered obese; people with a BMI of 40 or higher are severely obese. The BMI is considered a flawed tool, but it is widely used by doctors to screen for obesity.

“The dramatic increase in obesity is even more concerning because this is the level of obesity that is associated with the highest rates of cardiovascular disease and diabetes, as well as poorer quality of life,” said Solveig Cunningham, a global health professor and obesity expert at Emory University.

Cunningham, who was not involved in the new study, said it’s not clear why rates of severe obesity are rising, or why it’s higher in women. Factors could include the influence of hormones, the effect of childbearing or other reasons that need further study, she said.

The new study also found that obesity rates varied by education. About 32% of people with a bachelor’s degree or more reported obesity, while about 45% of those with a college or high school diploma or less reported obesity.

The new report follows data released earlier this month from US states and territories that showed obesity rates in 2023 will vary widely by place, from more than 41% of adults in West Virginia to less than 24% of adults in Washington, DC, with rates highest in the Midwest and South.

All U.S. states and territories have obesity rates above 20%. The data showed that in 23 states, more than 1 in 3 adults were obese. Dr. Alison Goodman, who leads a CDC team focused on population health, said that before 2013, no state had rates this high.

The color-coded US map tracking this change has gradually shifted from green and yellow, associated with lower rates of obesity, to orange and dark red, associated with higher prevalence.

“Sometimes, when you see all the red, it’s really discouraging,” Goodman said.

But, he said, the recent emphasis on understanding obesity as a metabolic disease and new interventions, such as a new class of weight-loss drugs, give them hope.

The most important thing is to prevent childhood obesity, Cunningham said. Even when people become obese, the goal should be to prevent further weight gain.

“It’s really hard to reduce obesity at the individual level and at the population level,” Cunningham said. “I think it’s not surprising that we’re not seeing a reduction in obesity prevalence.”