People taking popular GLP-1 weight loss medications such as Ozempic, Wegovy, Mounjaro, and Zepbound appeared to become less physically active after starting treatment, according to new research presented at ENDO 2026, the Endocrine Society’s annual meeting in Chicago. The findings challenge the assumption that losing weight naturally leads to increased movement and suggest that medication alone may not encourage a more active lifestyle.
The researchers found that adults with obesity who began GLP-1 receptor agonist therapy took fewer daily steps and spent less time performing moderate-to-vigorous physical activity after starting treatment. The decline persisted despite weight loss, highlighting the importance of combining medication with structured exercise and lifestyle interventions.
Examining Activity Before and After GLP-1 Therapy
The study focused on GLP-1 receptor agonists, a class of medications that includes semaglutide, marketed as Ozempic and Wegovy, tirzepatide, sold as Mounjaro and Zepbound, and older drugs such as liraglutide and dulaglutide.
These medications mimic naturally occurring gut hormones that suppress appetite, improve blood sugar regulation, and often produce substantial weight loss.
To objectively measure physical activity, the researchers used data from the U.S. National Institutes of Health’s All of Us Research Program, which combines electronic health records with information collected from consumer wearable fitness devices.
The investigators initially identified 1,950 adults with obesity who had started taking a GLP-1 medication.
After applying eligibility criteria requiring sufficient Fitbit data before and after treatment, the final analysis included 753 participants.
Women accounted for nearly 80% of the study population, and the average participant was just over 52 years old.
The researchers compared daily step counts and time spent in moderate-to-vigorous physical activity before and after participants began GLP-1 therapy.
Physical Activity Declined After Treatment Began
Following treatment initiation, average daily step counts fell from 5,047 to 4,487 steps per day, representing a reduction of more than 500 daily steps.
Time spent performing moderate-to-vigorous physical activity also declined, decreasing from an average of 28 minutes to 22 minutes per day.
The reduction in activity was most pronounced among men and among participants who experienced joint or muscle pain.
In contrast, factors such as older age, heart failure, or a previous stroke did not significantly alter the overall pattern, suggesting that reduced activity occurred across a broad range of health conditions.
Importantly, the researchers found no evidence that weight loss itself encouraged participants to become more active over time.
Even though carrying less body weight would generally be expected to improve mobility and reduce stress on joints, lower activity levels persisted after treatment began.
Why Exercise Remains Essential
Healthcare professionals have long emphasized that GLP-1 medications reduce not only body fat but also lean muscle mass.
Clinical studies of semaglutide and tirzepatide have shown that a meaningful proportion of weight lost during treatment comes from muscle as well as fat, making muscle preservation an important goal during therapy.
Lead author Sajana Maharjan of HSHS St. John’s Hospital in Springfield, Illinois, said the findings highlight the need to integrate structured exercise into obesity treatment from the beginning.
Regular resistance training helps preserve muscle mass and strength, while aerobic exercise supports cardiovascular fitness and metabolic health during weight loss.
The researchers suggest several possible explanations for the observed decline in activity.
Some patients may feel less urgency to exercise once they begin losing weight successfully through medication, while others may experience side effects such as nausea or fatigue that temporarily reduce motivation to remain physically active.
Without a structured plan to maintain or increase movement, patients may lose muscle strength and cardiorespiratory fitness even as their body weight improves.
Implications for Long-Term Obesity Care
According to the researchers, this is the first large-scale study to examine real-world physical activity patterns in adults taking GLP-1 receptor agonists using continuous wearable fitness tracker data.
Unlike self-reported exercise questionnaires, wearable devices such as Fitbit provide objective measurements of daily movement over extended periods.
The findings suggest that clinicians should view GLP-1 medications as one component of a comprehensive obesity treatment strategy rather than a standalone solution.
Obesity specialists increasingly recommend combining these medications with individualized exercise programs, nutrition counseling, and behavioral support to preserve muscle mass, maintain bone health, and optimize long-term metabolic function.
The researchers also propose incorporating wearable activity data into routine clinical care.
Continuous monitoring could allow healthcare providers to identify declining physical activity early and intervene with targeted strategies such as resistance training programs, physical therapy, digital coaching, or personalized exercise guidance.
Important Limitations
The researchers emphasize that the study demonstrates an association rather than a direct cause-and-effect relationship.
Because this was an observational analysis, it cannot determine whether GLP-1 medications themselves caused participants to become less active.
Other factors, including medication side effects, changes in health status, individual motivation, or lifestyle circumstances, may also have contributed to the decline in physical activity.
Nevertheless, the findings reinforce an important message for patients and healthcare professionals alike.
As the use of GLP-1 medications continues to expand worldwide, long-term health outcomes are likely to depend not only on successful weight loss but also on preserving muscle mass, maintaining physical fitness, and sustaining regular movement through ongoing lifestyle changes alongside pharmacological treatment.
