When people begin a GLP-1 weight-loss drug, they tend to move less, not more. That is the finding from a large wearable-tracker analysis presented at ENDO 2026, the Endocrine Society's annual meeting in Chicago.
Average daily steps fell from 5,047 to 4,487, a decline of 560 steps per day. Time spent in moderate-to-vigorous physical activity dropped from 27.9 to 22.2 minutes per day, according to the Endocrine Society press release.
The study, led by Sajana Maharjan, M.D., of HSHS St. John's Hospital in Springfield, Illinois, drew on the NIH's All of Us Research Program.
Of 1,950 adults with obesity who had started a GLP-1, 753 had enough Fitbit data before and after treatment for the analysis. The cohort was 78.6% women, with a mean age of 52.7 years.
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Why a small drop actually matters
560 fewer steps a day sounds minor. The concern is what it compounds with. GLP-1 receptor agonists include semaglutide, the active ingredient in Novo Nordisk's Ozempic and Wegovy, and tirzepatide, the active ingredient in Eli Lilly's Mounjaro and Zepbound.
These drugs reduce not just body fat but also lean muscle mass. Roughly 40% of the weight lost on semaglutide comes from lean mass, according to research presented at the Endocrine Society's 2025 annual meeting.
Layer a quieter daily routine on top of that muscle loss, and the challenge of protecting strength, bone density and metabolic health grows.
Certain groups in the ENDO 2026 analysis lost far more activity than the average. Men dropped an average of 986 steps a day, more than double the 445-step decline seen in women, according to Healio's coverage of the presentation.
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People with joint or muscle pain lost 679 steps a day. Those without pain lost just 22.
Exercise cannot be optional, the researcher argues
Maharjan framed the takeaway plainly in the release. "While many assume that weight loss leads naturally to increased physical activity, our study suggests otherwise," she said.
"The findings in our study reinforce that exercise cannot be optional for people taking these medications," she added. Patients "need targeted interventions that encourage physical activity alongside medication for obesity."
That message lines up with a growing body of research on GLP-1 users. A separate analysis found that, after losing weight on GLP-1 drugs, only exercise actually protected the heart over the following year.
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The findings do come with limits. This is a conference abstract, not a peer-reviewed publication, and it tracked only people who wore a Fitbit. It also cannot prove the drugs caused the drop in movement, only that the two changes moved together.
The practical takeaway is straightforward. Anyone starting a GLP-1 should treat resistance training and daily walking as part of the treatment, not an optional add-on, and discuss a movement plan with their doctor. Readers with joint or muscle pain, or existing cardiovascular concerns, should raise those specifically before starting the medication.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.