FRIDAY, Dec. 13, 2024 (HealthDay News) -- The U.S. obesity rate declined for the first time in a decade last year, coinciding with the rise of GLP-1 weight-loss meds, a new study finds.

Data on almost 17 million adults nationwide showed the obesity rate -- which has been rising for years -- fell from 46.2% of adults in 2021 to 45.6% in 2023, Harvard University researchers report.

Obesity was defined as having a body mass index (BMI) of 30 or above.

At the same time, the use of GLP-1 medications like Wegovy and Zepbound has surged, although the researchers said it's not possible to confirm a cause-and-effect relationship between the trends.

Still, they noted that, "The most notable decrease [in obesity] was in the South, which had the highest observed...dispensing rate," for GLP-1 medications.

The study was led by Benjamin Rader, an assistant professor of anesthesia at Harvard Medical School, and published Dec. 13 in the journal JAMA Health Forum.

As Rader's team noted, "the prevalence of obesity in the U.S. has increased for several decades. Some long-term forecasts estimate that this upward trajectory will continue, while others forecast a plateau."

The introduction of GLP-1 meds like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) into the marketplace has been a perhaps unexpected new factor in recent years, however.

Sales of the injected medications have soared, and the results in terms of weight loss have often been impressive. The drugs work by mimicking a hormone in the intestine that, among other things, helps folks feel full.

The new study tracked health insurance data from 2013 through 2023 on almost 17 million adults, most between the ages of 26 and 75. The data included almost 48 million BMI measurements, and a subset of participants were also tracked for their use of any GLP-1 medication.

Average adult BMI in the United States charted a slow but steady rise from 2013 (29.65 BMI) to 2021 (30.23), before leveling out in 2022 (30.24), the team said.

But then in 2023, average BMI dipped to 30.21 -- the first decline in a decade, according to Rader's team. The percentage of Americans who were obese also declined slightly that year.

Declines were steepest in the South and among older people (ages 66 to 75), the research showed. The rate of obesity among women fell more sharply than among men.

It's too early to credit GLP-1 meds with the welcome drop in obesity rates. Rader's team pointed out that, in the South, especially, the pandemic may have also played a role, since COVID was more often fatal for obese individuals.

Still, the overall news for Americans' health is good.

"While obesity remains a considerable public health concern, the observed reductions in obesity prevalence suggest an encouraging reversal from long-standing prior increases," Rader and team wrote.

More information

Find out more about GLP-1 meds at the Cleveland Clinic.

SOURCE: JAMA Health Forum, Dec. 16, 2024