A new study from experts at the University of Virginia warns that while GLP-1 drugs help many people lose weight, they may not improve heart and lung fitness, which is important for long-term health.
The researchers say that these drugs have clear benefits for people with obesity, type 2 diabetes, and heart failure, such as better blood sugar control and improved short-term heart and kidney health.
But they also highlight a serious concern: patients may be losing too much muscle along with fat.
GLP-1 drugs, such as those used to treat diabetes and obesity, cause the body to lose fat. However, they also reduce fat-free mass, which includes muscle. Muscle makes up about 40–50% of fat-free mass.
According to the researchers, 25–40% of the total weight lost with GLP-1 drugs comes from this important lean tissue. This is much more than the 8% fat-free mass lost per decade with normal aging.
One of the researchers, Dr. Zhenqi Liu, said some patients reported feeling like their muscles were disappearing while on these drugs. Losing muscle can harm posture, movement, and overall health.
It can even raise the risk of heart disease and early death. That’s why it’s important to make sure patients taking GLP-1 drugs are not already at risk of poor nutrition or muscle loss.
Dr. Liu and his colleagues, including PhD student Nathan R. Weeldreyer and exercise expert Dr. Siddhartha S. Angadi, looked at how these drugs affect cardiorespiratory fitness (CRF).
CRF, measured as VO2max, tells doctors how well the heart, lungs, muscles, and blood vessels work together during exercise. It’s one of the best indicators of overall health and risk of death.
People with obesity often have poor CRF, sometimes because they don’t have enough muscle, or because their muscles are filled with fat. Dr. Angadi stressed that CRF is more important than body weight when it comes to predicting risk of death.
A recent study of nearly 400,000 people showed that once CRF was considered, body weight didn’t matter as much.
In their review of published research, the UVA team found that while GLP-1 drugs improve some heart functions, they don’t lead to major improvements in VO2max. Some small studies show that exercise might help, but these studies were not strong enough to confirm this for sure.
The researchers concluded that GLP-1 drugs do help reduce body weight and fat, but they also reduce muscle mass and do not clearly improve heart and lung fitness. This could impact long-term health and lifespan. They are calling for more studies to understand the full effects of these drugs and to find ways to protect muscle and fitness during treatment.
There may be hope on the horizon. A new type of drug, a monoclonal antibody, may help prevent muscle loss in the future.
But for now, the team recommends that people taking GLP-1 drugs talk to their doctors about how to protect their muscle health. This might include eating enough protein, doing regular exercise, and checking for signs of malnutrition.
Dr. Angadi added that we still need more research to see if combining exercise with GLP-1 drugs can help improve cardiorespiratory fitness during treatment.
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The study is published in The Journal of Clinical Endocrinology & Metabolism.
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