By Annisa Sofia 
CHICAGO, ILLINOIS – A groundbreaking study presented at ENDO 2026, the Endocrine Society’s annual meeting, has unveiled a potentially counterintuitive finding: individuals with obesity who have achieved significant weight loss through popular medications like Ozempic, Wegovy, Mounjaro, and Zepbound have demonstrated a notable decrease in their physical activity levels. This research challenges a common assumption that shedding excess pounds naturally translates into greater mobility and a more active lifestyle.
The findings, which emerged from an analysis of data from the National Institutes of Health’s All of Us Research Program, suggest that the mechanisms driving weight loss with these medications may inadvertently lead to reduced physical exertion. This presents a critical new consideration for healthcare providers and patients navigating the landscape of obesity treatment.
The Rise of GLP-1 Receptor Agonists in Obesity Management
The medications under scrutiny belong to a class known as glucagon-like peptide-1 (GLP-1) receptor agonists. This innovative group of drugs, which includes semaglutide (marketed as Ozempic for diabetes and Wegovy for weight management) and tirzepatide (marketed as Mounjaro for diabetes and Zepbound for weight management), has revolutionized the approach to managing obesity and type 2 diabetes. Liraglutide and dulaglutide are other members of this influential drug class.
These medications work by mimicking the action of the natural GLP-1 hormone, which plays a crucial role in regulating appetite and blood sugar. By stimulating insulin release, slowing gastric emptying, and reducing appetite, GLP-1 receptor agonists can lead to substantial and sustained weight loss. Their efficacy has been widely documented, with clinical trials demonstrating average weight loss figures often exceeding 15% of body weight. For instance, the SURMOUNT-1 trial for tirzepatide reported an average weight loss of 22.5% in participants with overweight or obesity. Similarly, the STEP trials for semaglutide showed an average weight loss of around 15%.
However, the current research highlights a complex interplay between pharmacological weight loss and physical behavior. While these drugs are highly effective in reducing body mass, the study indicates they may also contribute to a loss of lean muscle mass. This loss of muscle can have significant implications for strength, metabolism, and overall functional capacity, making physical activity not just beneficial but arguably more critical than ever for maintaining health during and after treatment.
Unpacking the Fitbit Data: A Shift in Activity Patterns
To investigate the impact of these medications on physical activity, researchers led by Dr. Sajana Maharjan of HSHS St. John’s Hospital in Springfield, Illinois, analyzed data from a large, diverse cohort of individuals participating in the All of Us Research Program. This program, launched in 2018, aims to collect health data from one million or more people living in the United States, integrating electronic health records with data from wearable devices, genomic sequencing, and participant surveys to create a comprehensive health profile.
The study cohort comprised 1,950 adults diagnosed with obesity who had initiated treatment with a GLP-1 receptor agonist. From this group, 753 participants possessed sufficient wearable-device data to be included in the final analysis. The demographic breakdown revealed a predominantly female participant group, with 78.6% being women, and an average age of 52.7 years. This demographic reflects the broader population often seeking treatment for obesity.
The research team meticulously compared physical activity metrics collected through Fitbit devices before participants began their GLP-1 medication regimen and after they had started and achieved some degree of weight loss. The primary focus of the analysis was on two key indicators of physical activity: average daily step counts and minutes of moderate-to-vigorous physical activity (MVPA). MVPA is generally defined as any activity that causes a person to breathe harder and their heart rate to increase, such as brisk walking, jogging, cycling, or swimming.
A Consistent Decline: Fewer Steps, Less Vigorous Exercise
The results presented at ENDO 2026 painted a clear and consistent picture: a significant reduction in physical movement following the commencement of GLP-1 receptor agonist therapy. The average daily step count for participants dropped from 5,047 steps per day before treatment to 4,487 steps per day after initiating the medication. This represents a decrease of approximately 11%.
Equally striking was the decline in time spent engaged in moderate-to-vigorous physical activity. The average daily MVPA decreased from 28 minutes to 22 minutes per day, a reduction of about 21%. This suggests that not only were individuals walking less, but they were also engaging in fewer bouts of more strenuous exercise.
The study further identified specific subgroups that experienced even more pronounced decreases in physical activity. Men in the study showed larger declines in both step count and MVPA compared to women. Additionally, individuals who reported pre-existing joint or muscle pain exhibited a more significant drop in their activity levels. This finding is particularly noteworthy, as it could indicate that while the medication aids in weight loss, it might not alleviate the pain or discomfort that limits physical engagement for some individuals, or that the loss of muscle mass exacerbates these issues. Conversely, factors such as the presence of heart failure or a history of stroke did not appear to significantly alter the observed trends in physical activity decline.
Crucially, the researchers found no evidence to support the notion that weight loss achieved through these medications naturally spurred an increase in physical activity. The correlation did not manifest as an inverse relationship where more weight lost equated to more movement.
Implications and Expert Commentary
The study’s lead investigator, Dr. Sajana Maharjan, emphasized the critical implications of these findings. "While many assume that weight loss leads naturally to increased physical activity, our study suggests otherwise," Dr. Maharjan stated. "The findings in our study reinforce that exercise cannot be optional for people taking these medications. People need targeted interventions that encourage physical activity alongside medication for obesity."
This research is believed to be the first large-scale study to leverage wearable fitness tracker data to specifically examine physical activity patterns among adults using GLP-1 receptor agonists. The use of objective, continuous data from devices like Fitbits offers a more accurate and granular view of daily movement compared to self-reported activity levels, which can be prone to recall bias.
The implications of these findings are far-reaching for the clinical management of obesity. GLP-1 receptor agonists have been hailed as a significant advancement, offering a powerful tool for weight management. However, this new research underscores the need for a holistic approach that integrates pharmacological treatment with robust strategies to maintain or enhance physical activity.
A Call for Integrated Care Strategies
The decline in physical activity, particularly the loss of lean muscle mass that can accompany rapid weight loss, raises concerns about long-term health outcomes. Muscle mass is vital for metabolic health, bone density, and overall functional independence. A reduction in physical activity could potentially counteract some of the health benefits derived from weight loss itself, or even lead to a decrease in strength and mobility over time.
Healthcare providers prescribing these medications may need to proactively incorporate personalized exercise prescription and behavioral support to encourage continued physical activity. This could involve:
- Individualized Exercise Plans: Tailoring exercise recommendations based on a patient’s current fitness level, any existing physical limitations, and personal preferences.
- Behavioral Counseling: Providing strategies and support to overcome barriers to exercise, such as lack of motivation, time constraints, or perceived difficulty.
- Monitoring Muscle Health: Potentially integrating assessments of muscle strength and mass into routine check-ups for patients on these medications.
- Patient Education: Clearly communicating the importance of maintaining physical activity alongside medication for optimal long-term health outcomes.
The Endocrine Society, as the host of the ENDO 2026 meeting, is a leading professional organization for endocrinologists. While the society itself did not issue a formal statement on this specific study immediately following its presentation, research presented at such prominent scientific gatherings typically undergoes rigorous peer review and discussion within the scientific community. The findings are likely to stimulate further investigation and dialogue among endocrinologists and other healthcare professionals.
Future Research Directions
This study opens several avenues for future research. Understanding the precise mechanisms by which GLP-1 receptor agonists might influence physical activity is a key area. Is it a direct physiological effect, a psychological response to rapid weight loss, or a combination of factors? Further research could explore:
- Mechanistic Studies: Investigating whether changes in appetite hormones, neurotransmitters, or energy expenditure contribute to reduced activity.
- Long-Term Follow-up: Tracking activity levels over extended periods to understand if the decline is sustained or if individuals can be successfully re-engaged in physical activity.
- Intervention Effectiveness: Evaluating the efficacy of different types of exercise interventions designed specifically for individuals taking GLP-1 receptor agonists.
- Impact on Muscle Mass: Directly correlating activity levels with changes in lean muscle mass to better understand the interplay between these factors.
As the use of GLP-1 receptor agonists continues to expand, driven by their remarkable success in weight management, understanding and addressing the associated changes in physical activity will be paramount to ensuring comprehensive and sustainable health improvements for millions of individuals worldwide. This research serves as a critical reminder that while medications can be powerful tools, they are most effective when part of a well-rounded approach to health and wellness.
