Many Americans today are living with obesity, even with the advent of newer, more effective drugs like semaglutide (the active ingredient in Ozempic and Wegovy). It’s a problem that seems to be getting especially serious in kids, however. Research out today finds that the percentage of children with “extremely severe” obesity has surged in the U.S. over the past decade and a half.

Scientists at the University of California San Diego led the study, which examined nationally representative data of Americans’ health. Between 2008 and 2023, the rate of extreme obesity among U.S. children increased more than threefold, they found. The findings highlight a growing public health emergency, the researchers say, given the much higher prevalence of liver and other health problems among this group of children.

“[They’re] developing adult-type complications—fatty liver scarring, type 2 diabetes, metabolic syndrome—years before graduation. These conditions track into adulthood and shorten life expectancy,” lead author Phillipp Hartmann, an assistant adjunct professor of pediatrics at UCSD, told Gizmodo. “Treating them strains families, clinics, and the health care system.”

Hartmann runs a weekly liver clinic at Rady Children’s Hospital San Diego, where he helps treat children with metabolic dysfunction–associated steatotic liver disease (MASLD), more commonly known as fatty liver. These children typically have obesity as well, and Hartmann began to notice that the most obese children tended to have the worst liver inflammation and scarring. These cases prompted him and his colleagues to wonder whether the current system for diagnosing obesity in children might be outdated.

Obesity in children is defined as having a body mass index that’s at least in the 95th percentile for children of that specific age and sex. The Centers for Disease Control and Prevention classifies severe obesity as having a BMI 120% of the 95th percentile or greater (alternatively, a BMI of 35 or greater). The American Academy of Pediatrics has two separate categories (Class 2 and 3) for severe obesity, with the highest having a BMI 140% of the 95th percentile or greater (or a BMI of 40 and above). But the study researchers argue these distinctions still aren’t enough to capture the unique added risks seen in the most profound cases of obesity. They’ve proposed two more classes, which they’ve coined extremely severe obesity. Class 4 would be having a BMI between 160% and 180% of the 95th percentile, while class 5 obesity would be having a BMI 180% of the 95th percentile or greater.

To validate their argument, the researchers analyzed data from the National Health and Nutrition Examination Survey (NHANES), a nationally representative poll of Americans’ dieting and lifestyle habits regularly run by the CDC. As expected, they found that children with extremely severe obesity had much higher rates of diagnosed metabolic disease than children with less severe obesity. They were roughly sevenfold more likely to have fatty liver, eight times more likely to have severe insulin resistance, and ten times more likely to have advanced liver scarring, for instance.

They also found that around 1.13% of children in 2023 met the criteria for extremely severe obesity. While that’s still a small figure overall, it’s more than triple the percentage seen in 2008 (0.32%). With roughly 73 million Americans under 18 living in the U.S. today, that’s about 825,000 children who have extremely severe obesity. Rates of extremely severe obesity were higher among teens, boys, and non-Hispanic Black children. The team’s findings were published Wednesday in JAMA Network Open.

“Kids already well above a healthy weight keep climbing higher,” said Hartmann. “They now make up more than one out of every 90 children, and the trend continues to go up.”

Pediatric obesity in the U.S. has been on the rise, with about 19% of children affected today. And some of the reasons behind this overall rise, such as more children eating diets rich in calories and ultra-processed foods, likely also help explain why extremely severe obesity is climbing in kids, too. But there might be other factors involved for a subset of children, Hartmann notes, including a genetic vulnerability or the aftereffects of the pandemic on their stress and sleeping habits.

“Because these pressures overlap, weight gain is not merely a personal choice issue but a complex, environment-driven problem,” he notes.

There has been some positive news about obesity in America lately. The latest CDC data shows that the national obesity rate has finally stopped climbing, at least in adults. Some of this decline is likely driven by the emergence of more effective GLP-1 medications like semaglutide. But the same data also suggests that severe obesity hasn’t yet stalled. And as powerful as these newer drugs are, many people haven’t been able to access them due to shortages or their high costs and limited insurance coverage.

Hartmann says interventions like clearer product labeling, healthy food subsidies, and community programs emphasizing physical activity can possibly help prevent childhood obesity from happening in the first place. Programs that screen for fatty liver and other metabolic diseases may also be able to keep these cases from worsening. But ultimately, children living with extremely severe obesity need greater access to obesity treatment, which can include family-oriented lifestyle programs, new and older medications, and, for some cases, bariatric surgery.

“Given the limited availability of novel, highly effective weight-loss medications such as semaglutide, I strongly believe that patients—especially pediatric patients—with classes 4 and 5 obesity, who carry by far the highest health risks, should be prioritized for access to these treatments,” Hartmann said. “I hope our study encourages the development of clinical trials specifically tailored to this high-risk population. We would be very interested in serving as a participating site for such a trial.”

For now, Hartmann and his team will continue to investigate other aspects of extremely severe pediatric obesity, including whether the microbiomes of these children are distinct from others.