People with Obesity Tend to Move Less After Starting GLP-1 Medications, Study Finds

Key Takeaways: 

• Daily step counts and moderate-to-vigorous activity both dropped after adults with obesity started a GLP-1 receptor agonist, with no sign that weight loss prompted people to move more.
  
• Because these medications strip away lean muscle as well as fat, staying active matters for protecting strength and long-term health rather than being an optional extra.
  
• This is the first large study to draw on data from wearable fitness trackers in adults taking GLP-1 medications, and its authors argue for targeted support that builds activity in alongside treatment.
  
  
  

A counterintuitive picture of how people move

It is tempting to assume that as the weight comes off, people naturally become more active. New findings suggest the opposite may be closer to the truth. Adults with obesity who were losing weight on glucagon-like peptide-1 (GLP-1) receptor agonist medications significantly reduced their physical activity, according to a study being presented on Saturday at ENDO 2026, the Endocrine Society’s annual meeting in Chicago, Illinois.

That matters because activity is one of the main safeguards against an unwanted side effect of these treatments. GLP-1 receptor agonists such as semaglutide, liraglutide, dulaglutide and tirzepatide reduce not only fat but also lean muscle mass. This makes physical activity essential for preserving strength and long-term health, according to study lead Sajana Maharjan, M.D., of HSHS St. John’s Hospital in Springfield, Illinois.

How the study was carried out

The work was a retrospective pre–post cohort study, meaning researchers compared the same individuals before and after they started treatment. It drew on data from the National Institutes of Health’s All of Us Research Program, which links participants’ electronic health records with their Fitbit activity data, allowing the team to track real-world movement rather than relying on self-reported habits.

Among the 1,950 adults with obesity who started a GLP-1 medication, researchers studied 753 people who had enough wearable-device data for analysis. The cohort was predominantly female, at 78.6 per cent, with a mean age of 52.7 years.

For each person, the researchers compared physical activity before and after treatment began, focusing on two measures: daily step counts and minutes of moderate-to-vigorous physical activity (MVPA).

Steps and active minutes both fell

The direction of travel was clear. On average, daily steps decreased from 5,047 to 4,487 per day, while MVPA minutes fell from 28 to 22 per day after people began a GLP-1 receptor agonist medication.

Crucially, the study found no evidence that weight loss from these medications led to increased physical activity. The expected rebound in movement simply did not appear in the data.

Who saw the biggest changes

The decline was not evenly spread. The largest drops were seen in men and in people living with joint or muscle pain. By contrast, factors such as age, heart failure or a prior stroke did not change the results, suggesting the pattern held across a fairly broad range of circumstances.

Why activity cannot be an afterthought

For Dr Maharjan, the practical message is that exercise needs to be designed into treatment rather than left to chance:

“While many assume that weight loss leads naturally to increased physical activity, our study suggests otherwise. 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.”

Given that GLP-1 receptor agonists reduce lean muscle alongside fat, a fall in activity could compound the loss of strength, making structured support for movement an important part of care rather than a nice-to-have.

A first for wearable-data research

The study stands out for its method as much as its findings. It is the first large study analysing data from wearable fitness trackers among adults taking GLP-1 receptor agonists, offering a more objective window into everyday behaviour than questionnaires alone can provide. As these medications become more widely used, that kind of real-world evidence is likely to shape how clinicians and patients approach physical activity during treatment.

CCH insights:

This is a very interesting study, but it throws up more questions than answers. Firstly, were any of the participants receiving diet and lifestyle advice as they are supposed to? GLP-1 medications are designed as an adjunct to such advice, but these results suggest it was probably lacking from these patients’ treatment. Another question, of course, is why did physical activity drop? Further research is needed to understand what is the underlying reason for these results. But most importantly, this study is a reminder that GLP-1 therapy is not just about taking the medication, it requires diet and lifestyle advice and ongoing support and monitoring.

Source: Endocrine Society