A surprising new study reveals that people taking popular weight loss medications like Ozempic and Wegovy are becoming less physically active after starting treatment, despite successfully losing weight. Researchers analyzing fitness tracker data found that daily step counts and exercise time both declined after patients began taking these drugs, a trend that contradicts the common assumption that shedding excess pounds naturally makes movement easier.

Why Are GLP-1 Users Moving Less?

The medications studied belong to a class called glucagon-like peptide-1 (GLP-1) receptor agonists, which includes semaglutide (found in Ozempic and Wegovy), tirzepatide (Mounjaro and Zepbound), liraglutide, and dulaglutide. While these drugs are highly effective for weight loss, they reduce more than just body fat. They also contribute to a loss of lean muscle mass, which makes physical activity especially important for maintaining strength and overall health.

Researchers from HSHS St. John's Hospital analyzed data from the National Institutes of Health's All of Us Research Program, which combines electronic health records with Fitbit activity data. The study included 753 adults with obesity who had enough wearable device data to track their movement patterns before and after starting GLP-1 medications. Most participants were women (78.6%), with an average age of 52.7 years.

What Did the Activity Data Show?

The results painted a clear picture of declining movement. Average daily step counts fell from 5,047 steps to 4,487 steps per day, a decrease of about 560 steps. Time spent in moderate-to-vigorous physical activity (MVPA) also dropped, decreasing from 28 minutes to 22 minutes per day. The largest decreases were seen in men and in people who reported joint or muscle pain.

Importantly, the researchers found no evidence that losing weight with these medications led people to become more physically active. This finding challenges the widespread belief that weight loss naturally motivates people to exercise more.

"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," stated Dr. Sajana Maharjan, study leader at HSHS St. John's Hospital.

Dr. Sajana Maharjan, Study Leader at HSHS St. John's Hospital

How to Protect Muscle While Taking Weight Loss Medications

• Combine medication with structured exercise: Research presented at the European Atherosclerosis Society Congress found that semaglutide combined with exercise reduced fat mass by 45% while limiting lean muscle loss to just 8%, compared to 11% muscle loss with medication alone.
• Prioritize strength training and cardio together: The combination of semaglutide and exercise significantly improved grip strength and muscle fiber diameter, measures that neither medication nor exercise alone could achieve.
• Target organ-specific health improvements: Combination therapy improved inflammation in adipose tissue and the liver, reduced liver fat accumulation, and decreased atherosclerotic lesion area, suggesting that exercise amplifies the metabolic benefits of the medication.

A preclinical study using mice with diet-induced obesity found that semaglutide alone reduced fat mass by 31% but also caused an 11% reduction in lean muscle mass. However, when researchers added exercise to the treatment, fat loss increased to 45% while muscle loss was limited to just 8%. This suggests that pairing medication with physical activity is crucial for preserving strength and long-term health.

The research also revealed that only the combined intervention of medication plus exercise significantly improved measures of muscle function and strength. Neither semaglutide nor exercise alone produced significant improvements in these critical health markers, highlighting the importance of a comprehensive approach.

While the mouse study provides promising evidence, researchers emphasize that further research in humans is needed to confirm these findings. However, the results suggest that combining semaglutide with structured exercise could represent a more effective strategy for treating obesity, helping patients achieve substantial fat loss while preserving muscle health and physical function.

For people currently taking GLP-1 medications, the takeaway is clear: weight loss alone is not enough. Working with healthcare providers to develop a personalized exercise plan alongside medication may be essential for achieving the best long-term health outcomes and maintaining the strength and mobility needed for an active life.