Exercise cannot be optional for people taking these medications
As millions turn to GLP-1 medications in search of a lighter body, a study of 753 adults reveals a quiet paradox at the heart of modern weight loss: the drugs that shrink the body may also still the body. Presented at the Endocrine Society's annual meeting in Chicago, the research found that daily steps fell and moderate exercise declined meaningfully after patients began these medications — not because they felt worse, but because the expected link between weight loss and increased movement simply did not materialize. The findings remind us that medicine can alter the body's composition but cannot substitute for the human will to move, and that the pursuit of health has never been a passive endeavor.
- A large-scale study using real-world fitness tracker data has upended the assumption that losing weight naturally makes people more active — it did not.
- Daily step counts dropped by roughly 560 steps and moderate-to-vigorous exercise shrank by six minutes per day, small numbers that carry serious long-term consequences for muscle and metabolic health.
- GLP-1 drugs reduce lean muscle alongside fat, meaning patients who move less while on these medications risk becoming lighter but structurally weaker and more vulnerable to injury.
- Men and those living with joint or muscle pain showed the steepest declines in movement, pointing to specific populations who may need the most urgent support.
- Researchers are now calling on healthcare providers to treat exercise not as optional advice but as a prescribed, monitored component of any GLP-1 treatment plan.
When adults begin taking GLP-1 drugs like semaglutide or tirzepatide for weight loss, something unexpected unfolds: they move less. A study presented at the Endocrine Society's annual meeting in Chicago tracked 753 adults with obesity who wore fitness trackers after starting these medications. Their daily step counts fell from just over 5,000 to about 4,500, and time spent in moderate-to-vigorous exercise dropped from 28 to 22 minutes per day. These are not trivial shifts — they represent a measurable retreat from movement at precisely the moment the body needs it most.
The stakes are higher than the numbers suggest. GLP-1 medications are remarkably effective at reducing weight, but they also strip away lean muscle alongside fat. Without exercise to counteract that loss, patients can end up lighter but weaker — less metabolically resilient and more vulnerable to injury and decline. The drugs do the work of weight loss; exercise must do the work of preservation.
The study, led by Dr. Sajana Maharjan of HSHS St. John's Hospital in Springfield, Illinois, drew on data from the NIH's All of Us Research Program, linking electronic health records with Fitbit data. The cohort was predominantly women, with an average age of 52.7 years. What the researchers found challenged a widely held assumption: that a lighter body naturally wants to move more. The data showed no such effect. The largest declines appeared in men and in people reporting joint or muscle pain.
"Exercise cannot be optional for people taking these medications," Dr. Maharjan said plainly. The study — the first of its scale to examine wearable data in this population — arrives as millions rely on these drugs, often expecting medication alone to resolve their weight. The science now suggests a more demanding truth: the drugs work, but only in partnership with deliberate movement. The open question is whether healthcare systems will build the structures to make that partnership real.
When people start taking GLP-1 drugs like semaglutide or tirzepatide for weight loss, something unexpected happens: they move less. A study presented this month at the Endocrine Society's annual meeting in Chicago found that adults taking these medications significantly reduced their physical activity—the very thing doctors say they need most to stay healthy as the pounds come off.
The research tracked 753 adults with obesity who had started a GLP-1 receptor agonist and wore fitness trackers that recorded their daily movement. On average, their step count fell from just over 5,000 steps per day to about 4,500. Their time spent in moderate-to-vigorous exercise dropped from 28 minutes daily to 22 minutes. These are not trivial shifts. They represent a measurable retreat from activity at the moment when the body needs it most.
The reason matters. GLP-1 drugs—semaglutide, liraglutide, dulaglutide, tirzepatide—work by suppressing appetite and slowing digestion. They are remarkably effective at reducing weight. But they do something else too: they strip away lean muscle along with fat. That muscle loss is the problem. Without exercise to counteract it, people can end up lighter but weaker, with less metabolic resilience and greater vulnerability to injury and decline. The medications do the work of weight loss; exercise has to do the work of preservation.
The study, led by Dr. Sajana Maharjan of HSHS St. John's Hospital in Springfield, Illinois, used data from the National Institutes of Health's All of Us Research Program, which connects electronic health records with Fitbit data from thousands of participants. The cohort was predominantly women (78.6 percent) with an average age of 52.7 years. Researchers compared each person's activity levels before and after starting medication, looking for patterns.
What they found challenged a common assumption. Many doctors and patients expect that losing weight naturally leads to more movement—that a lighter body feels better and moves more freely. The data suggested otherwise. The study found no evidence that weight loss from these medications prompted increased physical activity. If anything, the opposite occurred. The largest declines in movement appeared in men and in people who reported joint or muscle pain. Age, heart failure, and prior stroke did not change the pattern.
Dr. Maharjan was direct about the implications. "While many assume that weight loss leads naturally to increased physical activity, our study suggests otherwise," she said. "The findings reinforce that exercise cannot be optional for people taking these medications. People need targeted interventions that encourage physical activity alongside medication for obesity."
This is the first large-scale study to examine wearable fitness tracker data among adults on GLP-1 medications. It arrives at a moment when millions of people are using these drugs, often with the expectation that medication alone will solve their weight problem. The research suggests a more complicated reality: the drugs work, but they require active partnership. Without deliberate effort to maintain movement and strength, patients risk trading one health problem for another—a lighter frame that is also a weaker one. The question now is whether healthcare systems will build the exercise support and accountability that the science says these patients need.
Notable Quotes
While many assume that weight loss leads naturally to increased physical activity, our study suggests otherwise. Exercise cannot be optional for people taking these medications.— Dr. Sajana Maharjan, study lead
The Hearth Conversation Another angle on the story
Why would weight loss make people move less? Doesn't a lighter body feel easier to move around in?
You'd think so. But the study found no evidence of that. People on these drugs are losing weight, but they're not naturally becoming more active. Some researchers think the medications themselves might affect energy or motivation, or maybe people feel they've "solved" the problem with the pill and don't see exercise as necessary anymore.
What's the actual danger here? They lost weight. Isn't that the goal?
Half the goal. The drugs strip away muscle along with fat. Without exercise, you end up lighter but metabolically weaker—less able to handle physical stress, more prone to falls and injury, especially as you age. You've solved one problem and created another.
Who was hit hardest by this decline in activity?
Men showed the biggest drops, and people with joint or muscle pain. That's the cruel part—the people who probably need to move most are the ones moving least.
So the solution is just telling people to exercise more?
The study's author said it needs to be more intentional than that. "Targeted interventions"—meaning doctors need to actively support and monitor exercise, not just prescribe the medication and hope for the best. It has to be part of the treatment plan, not an afterthought.