A study found that the adult obesity rate in the United States has decreased for the first time in a decade. This decrease is attributed to the recent release of obesity medications from the glucagon-like peptide (GLP-1) class, including Wegovy and Zepbound. However, there are also concerns that large-scale infectious diseases may have had an impact, making it premature to conclude that obesity medications are the direct cause of the decrease.
A research team led by Professor Benjamin Rader of Harvard Medical School analyzed approximately 48 million health insurance data records for around 17 million adults across the United States from 2013 to 2023. The team confirmed that the obesity rate, which had been steadily increasing, decreased from 46.2% in 2021 to 46% in 2022, and further to 45.6% in 2023.
In 2023, the average body mass index (BMI), calculated as weight divided by height squared, also fell to 30.21, indicating a decrease for the first time in a decade. The World Health Organization (WHO) defines obesity as a BMI of 30 or higher. The results of this study were published on Jan. 13 in the Journal of the American Medical Association (JAMA) Health Forum.
The Harvard Medical School research team believes that the release of new obesity medications is the primary background for the weight reduction trend. Weight-loss drugs from the GLP-1 class, such as Wegovy and Zepbound, have been shown through clinical trials to reduce weight and maintain it over the long term. Up until now, 1 in 8 U.S. adults have used Wegovy or Zepbound.
Previously, the Centers for Disease Control and Prevention (CDC) announced in October that the adult obesity rate in the U.S. began to decrease, according to the results of the U.S. National Health and Nutrition Examination Survey. According to the announcement, the obesity rate in U.S. adults increased from 30.5% in 2000 to 41.9% in 2020, but dropped by about 2 percentage points to 40.3% from 2021 to 2023. The CDC used data collected from clinical examinations that measured weight and height.
Wegovy and Zepbound are drugs that mimic the human hormone GLP-1. They work by slowing down the digestion of food in the stomach, leading to a feeling of fullness and suppressing appetite, thereby facilitating weight loss. While both surveys did not establish a precise causal relationship for the decrease in obesity rates, the research team noted that the timing was similar to when the GLP-1 obesity medications were released, suggesting they likely had a significant impact.
Denmark's Novo Nordisk developed a GLP-1 analog and obtained FDA approval in 2017 for a diabetes drug (Ozempic), which later evolved into the obesity drug Wegovy, launched in the U.S. in June 2021 due to its weight loss effects. U.S. Eli Lilly also launched Mountjaro as a diabetes treatment in 2022 as a GLP-1 analog and released the obesity treatment Zepbound in November 2023.
The research team confirmed that the obesity rate in the Southern region of the U.S. decreased the most during the tracking period. This also indicates a strong connection between obesity medications and the reduction in obesity rates. This Southern region had the highest number of prescriptions issued after the launch of the GLP-1 obesity medications in the U.S.
Professor Rader noted, "The most significant decrease in obesity rates occurred in the Southern region, which also had the highest prescription rate of GLP-1 medications at 6.0%." Following the South, the Midwest had a prescription rate of 5.1%, the Northeast 4.4%, and the West 3.4%.
Of course, it is still early to conclude that the introduction of GLP-1 drugs is the cause of the decrease in obesity rates. The research team pointed out, "Especially among obese individuals in the Southern region, there were relatively many deaths due to the novel coronavirus disease (COVID-19)," stating that the pandemic may have had a considerable impact on the decrease in obesity rates.
Reference materials
JAMA Health Forum (2024), DOI: https://www.doi.org/10.1001/jamahealthforum.2024.3685