Weight loss on GLP-1s may not translate to more exercise

Clinical takeaway: Don't assume weight loss will prompt patients to become more active. This study suggests the opposite may be true, underscoring the importance of structured physical activity counseling and monitoring.

Exercise is not optional for people taking GLP-1 medications. These drugs are known to reduce lean muscle mass alongside fat, making physical activity essential for preserving strength. In the first large study to use wearable fitness tracker data to examine activity patterns in adults on GLP-1 therapy, the finding was the opposite of what clinicians might hope. Patients moved significantly less after starting treatment, not more.

Daily steps dropped by an average of 560 per day after GLP-1 initiation, falling from 5,047 to 4,487, and moderate-to-vigorous activity minutes fell from 28 to 22 per day. Men experienced more than twice the step decline of women. People with joint or muscle pain also showed significantly greater reductions in activity than those without. Age, morbid obesity, heart failure, and prior stroke were not associated with differences in activity change.

The retrospective study drew on NIH All of Us Research Program data linking health records with Fitbit activity tracking. Of 1,950 adults with obesity who started a GLP-1 medication, 753 had enough wearable data for analysis. The cohort was predominantly female and middle-aged.

Moderate-to-vigorous activity dropped by an average of nearly 6 minutes per day across the cohort. Sex differences were particularly striking: men lost 15 minutes of moderate-to-vigorous activity per day on average, compared with 3 minutes for women. These findings were presented at the Endocrine Society's annual meeting, ENDO 2026, and have not yet undergone peer review.

The study adds an important caveat to the GLP-1 success story. While these medications produce meaningful weight loss, they are known to reduce lean muscle mass as well as fat, and patients who move less during treatment may be at risk of accelerated muscle loss and reduced long-term functional capacity. The authors argue this makes exercise counseling not just advisable but essential.

"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," said lead author Sajana Maharjan, M.D., of HSHS St. John's Hospital.

Source: Maharjan S, et al. Endocrine Society Annual Meeting, Abstract SAT-714. June 13, 2026. Losing Pounds, Not Gaining Steps: The Paradox of GLP-1 Receptor Agonist Therapy