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People taking the new anti-obesity medications must make time for physical activity, say KU researchers

Physical activity is still important for the numerous holistic health benefits exercise provides, even for those losing weight on popular new drugs.

Woman walking outside carrying hand weights for exercise
KU researchers recommend 150 minutes a week of physical activity, including two days of muscle-strengthening activities, for those taking the new class of anti-obesity drugs

Game-changing. Revolutionary. Unprecedented. These are the kinds of adjectives commonly used to describe the new class of anti-obesity drugs that includes Ozempic, Wegovy and Mounjaro. These prescription medications mimic the actions of gut hormones that stimulate the release of insulin, which lowers blood sugar after eating and causes the stomach to empty more slowly. These drugs are so effective at suppressing appetite and helping people lose weight that manufacturers are struggling just to keep up with the demand.

The weight loss that people achieve with these medications, however, does not provide all the health benefits they need. And these drugs have necessitated a re-focusing of lifestyle factors for the people who take them, including recommendations for physical activity and exercise, said John Jakicic, Ph.D., research professor in the Division of Physical Activity and Weight Management at the University of Kansas Medical Center.

Jakicic and Renee Rogers, Ph.D., senior scientist in the KU Medical Center Division of Physical Activity and Weight Management, have published one of the first peer-reviewed articles about how physical activity fits into the treatment of obesity when using these anti-obesity medications. The article appeared in Obesity, the journal of The Obesity Society, on October 17, and Jakicic discussed these topics on a recent Morning Medical Update by The University of Kansas Health System.

“These medications have changed how we need to think about activity,” said Jakicic. “They can take care of the weight loss for us, so our focus should not be on how much activity we need to do to lose more weight; it should be about all the other things the activity does that the weight loss medications don’t do.”

These include cardiovascular fitness and muscle strength, which exercise improves even if someone doesn’t lose an ounce. “So it’s not about having people exercise in order to have more weight loss,” said Jakicic. “It's about rethinking activities so that people understand even if you're losing all this weight, you still need to be active. Patients need to understand that, and clinicians need to understand that.”

The researchers also state that with these new medications, the current recommendation of 200 to 300 minutes of exercise a week to lose weight might be no longer necessary. They propose instead that the public health recommendation to reduce sedentary behavior, which is 150 minutes per week of moderate-intensity physical activity (such as a brisk walk) and two days per week of resistance exercise, may be sufficient for people taking anti-obesity drugs.

"These medications have changed how we need to think about activity."

More complicated is the loss of lean mass that accompanies weight loss. When people shed pounds through diet and exercise without medications, lean mass accounts for 15% to 20% of their weight loss, Jakicic said. For reasons that are not yet clear, when people take the new medications, that percentage jumps to as much as 40%.

It’s easy to conclude that the solution to this reduction in lean mass is exercise and more exercise, especially resistance training because it builds muscle. But the researchers point out that lean mass includes more than just muscle; it is all the body’s organs and tissues except fat, and it is not yet clear how much of the lean mass lost during medication-aided weight loss is actually muscle. Moreover, even when people add resistance exercise to a weight loss program, they still lose some muscle mass.

Jakicic and his colleagues assert that the focus should be on improving muscle quality rather than increasing muscle mass. “Muscle quality is about making the muscle more functional rather than having more of it,” Jakicic said. “Within eight weeks of starting an exercise resistance training program, you will have no increase in muscle mass, but you will get stronger. And if you have better muscle quality, not only will you have more strength, but you also will have better control of your insulin and glucose.”

Researchers in the physical activity and weight management division at KU are launching a number of studies related to these new medications, weight loss and physical activity. This includes a pilot study conducted by Rogers, and supported by the Kansas Center for Metabolism and Obesity Research, looking at the effectiveness of both aerobic training and resistance training in people taking anti-obesity drugs.

“Our goal is to provide evidence to improve care for people taking these medications,” Jakicic said. “We have a perspective now, but we're also doing research that may change that perspective as we work to improve future treatments.”

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