People using GLP-1 medications such as Ozempic and Wegovy may be losing more than body fat, according to a new study that found physical activity levels dropped significantly after patients began taking the drugs.

Researchers reported the findings ahead of the Endocrine Society’s annual meeting, ENDO 2026, in Chicago, where the data will be presented.

The study analyzed adults with obesity who used GLP-1 medications for weight loss and found that participants “significantly reduced” their activity once on treatment.

Lead author Dr. Sajana Maharjan of HSHS St. John’s Hospital in Springfield, Illinois, said these drugs—semaglutide, liraglutide, dulaglutide, and tirzepatide—can decrease both fat and lean muscle mass.

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“Physical activity is essential for preserving strength and long-term health,” Maharjan emphasized in a press release from the Endocrine Society.

The research used data from a National Institutes of Health program that connected patient records with wearable fitness tracker data, offering an objective look at daily activity.

Among 753 participants analyzed, with an average age of 52.7 years and mostly female, daily steps fell from 5,047 to 4,487 on average once they started medication.

Moderate to vigorous activity time also dropped, from 28 minutes to 22 minutes per day. The greatest declines were observed in men and in individuals with joint or muscle pain.

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Factors such as age, previous stroke, or heart failure did not appear to influence these results.

Despite assumptions that weight loss would naturally boost motivation to move more, the study found no evidence of increased activity after starting treatment.

“The findings in our study reinforce that exercise cannot be optional for people taking these medications,” Maharjan said, calling for more support programs that promote activity during treatment for obesity.

Researchers noted that the study was retrospective and observational, showing an association but not a cause. They also acknowledged limits, including that most participants were middle-aged women.

The analysis did not measure participants’ preexisting exercise routines, motivation levels, or whether doctors provided guidance about physical activity before beginning medication.

Dr. Peter Balazs, a hormone and weight-loss specialist in New York and New Jersey, told Fox News Digital that weight loss alone does not guarantee improved fitness or energy levels.

“Being in a calorie deficit can cause the body to conserve energy, resulting in a lower metabolic rate,” Balazs explained.

He added that side effects such as fatigue, nausea, or digestive problems might discourage movement.

For people using GLP-1 drugs, Balazs said exercise must remain a priority. He recommends consistent strength training and everyday movement such as walking to help maintain lean muscle mass and long-term metabolic health.

He also pointed to the role of exercise in supporting bone, joint, and cardiovascular health, stressing that without adequate activity, “a significant portion of weight loss may come from muscle rather than fat.”

Balazs cautioned that workout routines need to be adapted to each person’s fitness level, mobility, and injury risk.

“This is particularly important for patients with a high BMI who may have mobility limitations or lower baseline fitness,” he said. “It’s important to consider injury risk, long-term adherence and the potential for early burnout.”

Not all experts agreed with the study’s conclusions. Dr. Amanda Kahn, a board-certified internist and longevity specialist, said the findings do not match what she sees in her practice.

“Weight loss often serves as the impetus that motivates patients to become more physically active and more engaged in their overall health,” Kahn said in her interview with Fox News Digital.

She said successful outcomes depend heavily on physician oversight, including monitoring nutrition, resistance training, and protein intake along with medication.

“The success of GLP-1 therapy is directly tied to the expertise of the provider,” Kahn said. “When prescribed thoughtfully—with attention to nutrition, resistance training, body composition and laboratory monitoring—these medications can help patients lose weight while becoming healthier, stronger, and more motivated to exercise.”

Kahn said patients should never be left to “self-manage” while using GLP-1 drugs. She monitors for signs of muscle loss, low protein intake, or excess fatigue and adjusts or pauses treatment when needed.

If those issues arise, Kahn said they show a “monitoring problem” rather than a drug problem, as patients require close clinical supervision during treatment.