People taking blockbuster obesity medications like Ozempic and Wegovy are exercising less after shedding pounds, not more, according to new research that challenges common assumptions about how weight loss affects physical fitness.
The finding emerged from an analysis of nearly 750 adults presented at the Endocrine Society's annual meeting in Chicago. Researchers tracking Fitbit data found that patients on GLP-1 receptor agonists experienced measurable drops in daily movement even as their weight fell.
Average daily step counts plummeted from roughly 5,000 to 4,500 steps per day. Time spent in moderate-to-vigorous exercise declined from 28 minutes to 22 minutes daily. The steepest declines appeared among men and people reporting joint or muscle pain.
The medications examined, which include semaglutide, tirzepatide, and liraglutide, represent a powerful new tool for weight loss. But these drugs strip away more than just fat. They also reduce lean muscle mass, making physical activity crucial for maintaining strength and function.
Sajana Maharjan, the study's lead researcher at HSHS St. John's Hospital in Springfield, Illinois, stressed that exercise cannot be sidelined during treatment. "Our study suggests that weight loss does not naturally lead to increased physical activity," Maharjan said. "People need targeted interventions that encourage physical activity alongside medication for obesity."
The research drew from the National Institutes of Health's All of Us Research Program, which combines electronic health records with wearable fitness data. The team began with 1,950 adults on GLP-1 medications but narrowed the final analysis to 753 participants with sufficient tracker data. Most were women, with an average age of 52.7 years.
Previous factors like age, heart failure, or prior stroke did not explain the activity declines, suggesting the effect cuts across demographic lines. The researchers found no evidence that weight loss itself motivated people to move more, an assumption that underpins much weight loss advice.
This marks the first large-scale study using wearable device data to map activity patterns among GLP-1 users, revealing a gap between what many expect and what actually happens once treatment begins.
Author Jessica Williams: "The real story here isn't that people get lazy after losing weight, it's that these powerful drugs change the equation in ways we're only starting to understand, and doctors need to actively push exercise rather than assume patients will do it naturally."
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