Share on PinterestNew reserach suggests that msucle loss with GLP-1s may not be as high as previously thought. Bloomberg/Getty Images
- While past studies show that adults taking a GLP-1 medication can lose between 5-15% of their starting body weight, other research reports that a good portion of that weight loss comes from muscle loss.
- A new study says, via a mouse model, that muscle loss from GLP-1 medications like Ozempic may not be as high as recently thought.
- Researchers also found that the decrease in lean muscle mass was not all from skeletal muscles, but from other body tissues, including the liver.
Recent polls estimate that one in every eight adults in the U.S. have taken a glucagon-like peptide-1 receptor agonist (GLP-1) — a class of prescription drugs originally used to treat type 2 diabetes that has gained popularity as a method of weight loss.
Types of GLP-1 medications include semaglutide, sold under the brand names Ozempic and Wegovy, and tirzepatide, sold under the brand names Zepbound and Mounjaro.
Past studies show that adults taking a GLP-1 medication can lose between 5-15% of their starting body weight within one year.
However, other research reports that about 25-39% of that weight loss is from muscle loss.
Now, a new study recently published in the journal Cell Metabolism says, via a mouse model, that muscle loss from GLP-1 medications like Ozempic may not be as high as recently thought.
Researchers also found that the decrease in lean muscle mass was not all from skeletal muscles, but from other body tissues, including the liver.
Lean muscle mass loss not just from skeletal muscles
For this study, researchers used a mouse model to determine how GLP-1 medications like Ozempic affected lean muscle mass.
Upon analysis, researchers found that Ozempic-related weight loss in mice resulted in a lean muscle mass decrease of about 10%, which is less than some previous studies report.
Scientists report that as the mice lost weight, some skeletal muscles did decrease, while other muscles stayed the same. Researchers state that the muscle mass decrease is a return to baseline, as gaining fat is usually accompanied by a gain in skeletal muscle.
Researchers found some mice experienced a decrease in strength in skeletal muscles that stayed almost the same size.
Additionally, researchers found that a good portion of the decrease in lean muscle mass did not come from skeletal muscles, but rather other tissues in the body, such as the liver, which they report reduced in size by almost half. It is not uncommon for the liver to decrease in size during weight loss, which can help reduce a person’s risk for fatty liver disease.
“If we want to really help the individuals who may be losing muscle mass, then we need to know that they’re actually losing muscle mass,” Katsu Funai, PhD, associate professor of nutrition and integrative physiology in the University of Utah College of Health and the senior author on the study says in a press release. “We have data in mice that suggest that things are not as straightforward as they might seem.”
Working with a dietitian while taking GLP-1s
Medical News Today spoke with Seth Kipnis, MD, FACS, FASMBS, director of bariatric and robotic surgery at Hackensack Meridian Jersey Shore University Medical Center in New Jersey, about this study, who commented that a drop in lean muscle mass is expected.
Some muscle loss is inevitable
“Any patient with a restricted diet and poor nutrition/protein will have a drop in muscle mass. The key of any weight loss program, surgical, medical or GLP-1 is adequate nutrition. Working with a registered dietitian is key to long-term success and avoiding complications of malnutrition.”
— Seth Kipnis, MD, FACS, FASMBS
“More and more people are taking these medications on a regular basis,” he continued. “They are working well to control weight. We should know the side effects that can be caused in the long term so that patients can be counseled on how to avoid long-term issues.”
Kipnis said he would like to see better long-term data as the next steps in this research.
“And are different outcomes found depending on the prescriber and the type of follow-up,” he added. “It is our assumption that specialists in weight management and nutrition will have better outcomes than a primary care doctor that treats every disease. Obesity is a unique disease that requires specialists to manage.”
Human trials needed to further analyze GLP-1s and muscle loss
MNT also talked to Kais Rona, MD, a bariatric surgeon of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA.
“As a physician who has treated and continues to treat many patients with GLP-1 medications such as Ozempic, I found this study quite interesting,” Rona said. “Although the data in this study cannot be extrapolated directly to humans, it does shed some light on potentially important physiologic effects of the medication.”
“The decrease in lean mass with GLP-1 use was associated with a lesser decrease in skeletal muscle mass and a greater decrease in the size of metabolically active organs such as the liver. This can have important physiologic effects on metabolism and overall health. We also see a decrease in liver mass in patients undergoing weight loss surgery, which often leads to beneficial health effects. Importantly, this study also highlights the importance of determining the functional impact of muscle loss and whether that is reflected in a loss of strength as well.”
— Kais Rona, MD
“It’s extremely important to continue to study the potential side effects, including the loss of lean muscle mass, associated with GLP-1 medications as it can have major effects on our healthcare system as a whole,” Rona added. “Furthermore, we need to continue to broaden our understanding of the physiologic effects of these medications to optimize patient safety and overall outcomes.”
Rona said the next best research step would be to perform randomized-controlled trials in humans to further analyze the effects of GLP-1 medications on lean mass as well as skeletal muscle mass.
“It would be important to evaluate its effects on muscle strength as well as function,” he added. “Also to determine whether certain areas of the body are more susceptible to muscle loss as well as identifying preventive strategies to combat muscle loss.”
