Have We Been Overstating GLP-1 Muscle Loss?

8 min readIf you’ve spent any time reading about GLP-1s or taking one yourself, you’ve probably heard the incessant warnings that the obesity drugs can cause significant muscle loss. And if you haven't, here's the gist: Medications like Ozempic, Wegovy, and Zepbound can lead to major weight loss, but people are starting to worry that a portion of that weight can come from muscle rather than fat.The thing is, though, the warnings around GLP-1s have made it sound like these medications are uniquely and highly destructive to muscle—but recent research is starting to suggest otherwise.A small study published this spring in Cell Reports Medicine was one of the first to look at actual muscle size and strength in people taking a GLP-1 (many prior studies looked instead at just lean body mass, which encompasses more than just muscle—more on that, below). The results? Not as worrisome as the headlines led you to believe.Losing some muscle is definitely a valid concern anytime someone loses weight, says study author Henning Langer, PhD, who leads the Muscle Wasting Laboratory at Charité in Berlin, but “there does not seem to be anything particularly negative about the type of weight loss that is achieved via GLP-1 medicines.”Have all the muscle-loss warnings gotten ahead of the science? Some experts think that’s the case, but that doesn’t mean the concern should be brushed aside. Here’s what you need to know, per the latest research and experts.Meet the experts: Henning Langer, PhD, is a researcher and the head of the Muscle Wasting Laboratory at Charité in Berlin. Stuart Phillips, PhD, is a distinguished university professor and chair of the department of kinesiology at McMaster University. Mir Ali, MD, is a bariatric surgeon and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center. Robert F. Kushner, MD, is a professor emeritus at Northwestern University Feinberg School of Medicine. Pooja Gidwani, MD, is an internal and obesity medicine physician.Lean body mass is not the same thing as muscle.First, some context for where all the GLP-1 muscle loss claims come from: A lot of the alarm around GLP-1s and muscle loss traces back to body composition research, including the STEP 1 semaglutide sub-study from 2021 and the SURMOUNT-1 tirzepatide sub-study from 2025. Both looked at how body composition changed while taking the meds and found that people lost about 10 percent of lean body mass while taking a GLP-1. The confusion came when lean mass got equated to muscle.Lean body mass is basically everything in your body that isn’t fat, Langer explains. Muscle is part of it, but so are your organs and the water and connective tissue throughout your body. In fact, he estimates that only about half of lean body mass is actually muscle.So, when a scan shows that someone’s lost lean mass, it doesn’t mean all of that loss came from muscle. The liver, for example, can shrink quickly during weight loss as it uses stored glycogen and fat, says Stuart Phillips, PhD, chair of the department of kinesiology at McMaster University. Glycogen also holds water, so losing those stores can register as a decline in lean mass without representing the same amount of lost muscle tissue, he explains.“The story is more nuanced than ‘GLP-1s melt muscle,’” says Phillips. In the STEP 1 semaglutide body-composition sub-study, for example, participants lost both fat and lean mass, but because fat dropped proportionally more, lean mass made up a larger share of their body weight afterward. That’s a favorable change in body composition, Phillips explains, but it still doesn’t tell us exactly how much muscle participants kept, or whether they got stronger or weaker. “A higher lean-mass percentage is not a muscle-preservation certificate,” he says.To get a clearer picture, researchers need to track muscle itself and test what it can do. MRI and CT scans can measure muscle size more directly than a scan of total lean mass, explains Phillips, but they still can’t tell you how strong someone is. That requires separate testing, like measuring grip strength or how easily someone can get up from a chair. Following both over a period of time can help show whether someone is maintaining muscle and strength as they lose weight.Muscle size only tells part of the story.It’s important to keep in mind that even when someone’s muscles shrink in size, it doesn’t automatically mean the person lost strength. In Langer’s study, which looked at just 10 men taking semaglutide for 12 weeks, participants’ thigh muscles shrank slightly, but their grip strength and ability to straighten their knees against resistance actually stayed the same. Translation: They may have lost muscle size, but they didn’t lose muscle strength. Langer says some of that decrease in size might have come from losing fat, stored carbs, and water within the muscle itself rather than a major loss of the muscle tissue that does the actual work.Still, the newest study leaves important questions unanswered. Beyond its small sample size and short duration—and the fact that there were no women involved—it can’t tell us whether the results apply to older adults or people with conditions like heart failure, cancer, or neuromuscular disease, explains Langer. We’d need bigger studies that follow people for longer periods of time.Overall, though, research suggests that GLP-1s actually help people feel like stronger, more mobile versions of themselves. People in GLP-1 trials often report being able to move more easily and feeling better overall, even when they lose some lean mass, says Robert F. Kushner, MD, professor emeritus at Northwestern University Feinberg School of Medicine. For example, a 2024 analysis of two clinical trials looked at women with obesity and a type of heart failure in which the heart pumps normally, but is too stiff to fill properly. After a year, women taking semaglutide said they felt better and had an easier time being physically active than those taking a placebo. They could also walk farther in a six-minute test.In his practice, Mir Ali, MD, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center, says he doesn’t often see muscle loss that noticeably affects a patient’s strength or daily life. “I occasionally have a patient complain of fatigue or weakness, but this usually resolves over time,” he says.So, do you still need to care about muscle loss when taking a GLP-1?Some people should still pay closer attention to muscle loss when taking a GLP-1, particularly if they already have less muscle to begin with or struggle to maintain it.“These include patients over 65 years of age, those with underlying medical problems such as chronic kidney or heart disease, patients who start treatment with a low muscle mass or lose excessive amounts of weight,” says Dr. Kushner. (There isn’t one number that counts as “excessive” for everyone, so Dr. Kushner recommends checking in with your provider if you’re consistently losing more than about two to three pounds a week or 5 percent of your body weight in a month, especially if you’re struggling to eat enough or feeling weaker.) A history of repeated dieting or low protein intake can add to the risk of muscle loss, Phillips adds.Women in perimenopause and after menopause should also pay attention to muscle and bone health since changes in estrogen can affect bones and body composition, while aging can make maintaining muscle harder. “If a woman is going through that transition and also losing a significant amount of weight, I want to be pretty deliberate about resistance training, adequate protein, and making sure we're not seeing a major decline in muscle mass,” says Pooja Gidwani, MD, an internal and obesity medicine physician.How to Protect Muscle While Taking a GLP-1The reassuring news is that muscle loss isn’t something you simply have to watch happen—whether you’re on a GLP-1 or not. The two biggest levers (resistance training and adequate protein) are fairly simple, even if they take some intention. Here’s what you can do to preserve your muscles.Strength-train at least twice a week.If you’re only going to prioritize one kind of exercise, make it strength training. Protein gives your body what it needs to maintain muscle (more on that in a second), and lifting gives it a reason to keep that muscle around. As Phillips puts it, “Resistance training is muscle-preserving medicine.”Eating enough protein matters, but adding more without strength training does relatively little to preserve muscle, Phillips explains. “Getting the training in matters more than fine-tuning your protein target,” he says.His minimum recommendation is two full-body sessions each week. You don’t need an elaborate workout routine or a bodybuilder’s schedule to accomplish that. Machines, dumbbells, resistance bands, and bodyweight exercises can all work. The important part, he explains, is working all the major muscle groups (legs, glutes, back, chest, shoulders, arms, and core). As you get stronger, you can gradually add weight, use a stronger resistance band, or add more reps to keep those muscles challenged.Want a science-backed, trainer-created program to follow? The WH+ GLP-1 Strength Plan includes three full-body strength workouts per week, plus nutrition guidance and workout trackers.Get our GLP-1 Strength Training Plan hereEat your protein first.When you fill up quickly, the order in which you eat can make a big difference. Try starting out with the protein portion of your meal so you get some in before you feel too full.For someone with obesity, Phillips recommends using a reference weight—not your actual weight—to estimate your protein goal because having more body fat doesn’t increase protein needs proportionally. Assuming you have normal kidney function, one option for a reference weight is to use the weight that corresponds to a BMI of 25 for your height. For someone who’s about 5'5" tall, that’s 150 pounds, which works out to roughly 80 to 110 grams of protein a day using his recommended range of 1.2 to 1.6 grams per kilogram. This is a starting point—not an exact requirement or a weight you need to reach. A health care provider or registered dietitian can help personalize it.Notice whether movement gets easier or harder.The scale can tell you if you’ve lost weight, but it can’t determine whether you’re keeping your strength. You’re the best judge of that. Pay attention to what you’re lifting at the gym and how you feel going about your regular everyday activities.Tell your provider if you’re feeling noticeably weaker during any of it. “Needing your arms to push yourself out of a chair when you didn't before, having more difficulty with stairs, or noticing a real change in grip or ability to carry things can indicate declining strength,” says Dr. Gidwani. “I would want to evaluate that rather than assuming it's just part of losing weight.”Know when to focus on maintaining.You don’t have to keep losing weight for treatment to be successful. Dr. Gidwani, for example, doesn’t automatically increase a patient’s GLP-1 dose just because the dosing schedule allows it. “If they're responding well, their appetite is controlled and they're losing weight at a reasonable rate, I may keep them at that dose, but if they can barely eat, are consistently unable to get enough protein or calories, are losing too fast, or we're seeing changes in strength or lean mass, I'm going to reassess the dose,” she says. Those too-high doses are really where people are most at risk for losing muscle and strength, she explains.Remember: Some lean mass loss can happen with weight loss, whether it comes from medication, calorie restriction, or bariatric surgery. The goal, Phillips says, is “high-quality weight loss,” or losing fat while preserving as much muscle, strength, and function as possible—which means tracking more than pounds lost. If you’re getting weaker or struggling to eat enough, always bring it up with your provider, even if your weight loss is going exactly as planned. But just because you’re taking a GLP-1 doesn’t automatically mean your muscles are doomed.Find the Perfect Women’s Health Training Program for YouJenn Sinrich is a journalist, editor, and content strategist with more than a decade of experience creating high-performing lifestyle, travel, health, and parenting content for top-tier media brands. Her work has appeared in Parents, Women’s Health, SELF, Brides, Marie Claire, and dozens of other national outlets. In addition to reporting and writing, Jenn collaborates with leading consumer brands to develop SEO- and AEO-driven content strategies, elevate brand voice, and create compelling stories that convert and resonate, especially with women and families. She specializes in bridging editorial storytelling with data-backed strategy to drive traffic, consumer loyalty, and engagement. When she’s not working, you can find her running on her Peloton or chasing after her three kids Mila, Leo, and Eli who inspire so much of her work.