If you are taking semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound), you have probably read that GLP-1s make you lose muscle. The real picture is more specific — and more manageable — than the headlines. Here is what the published research says, with every number linked to its source.
The line repeated across social media is that “40% of the weight you lose on a GLP-1 is muscle.” That number is a misreading of a real finding.
The figure comes from a body-composition analysis of the STEP 1 semaglutide trial, where about 38% of the weight lost was lean body mass2,1. Lean body mass is everything that is not fat — muscle, yes, but also water, organs, bone and connective tissue. Muscle is roughly half of it. The 2025 joint society advisory does that arithmetic explicitly and concludes this “corresponds to ∼20% of total weight reduction being muscle loss.”1
Two other things worth knowing, because they rarely make it into the headline:
Estimates across the literature vary widely — one review notes studies reporting anywhere from 15% to 60% of weight lost as lean mass, depending on how it was measured4. Anyone quoting you a single confident number is oversimplifying.
In 2025 four professional bodies — the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society — published a joint advisory specifically on nutrition during GLP-1 therapy. It is the most directly relevant guidance that exists for this question.1
During active weight loss
1.2–1.6 g/kg
of body weight per day — the range the advisory reports as proposed during active weight reduction1
Or, as a simpler target
80–120 g
per day. The advisory notes an absolute target “may enhance adherence while ensuring adequate intake”1
For scale: at 1.2–1.6 g/kg, someone weighing 90 kg (about 200 lb) lands at roughly 110–145 g of protein per day. You can work out your own number with our protein calculator.
Two caveats worth stating plainly. First, the advisory describes these targets as ones that “have been proposed” — it is consensus expert guidance, not a graded evidence recommendation. Second, you will find much higher numbers quoted online, often 2.3–3.1 g/kg. That range comes from a sports nutrition position stand addressing resistance-trained athletes in a deliberate cut7, and it does not transfer to someone losing weight on obesity pharmacotherapy. Adults over 65 have their own guidance, typically 1.0–1.2 g/kg and higher with illness8.
This is the part most protein-focused articles leave out, and the advisory is blunt about it: “increased protein intake alone is likely inadequate to support the preservation of muscle mass in the absence of structured resistance/strength training.”1
The size of the protein-only effect backs that up. Pooling 24 randomized controlled trials of higher-protein versus standard-protein weight-loss diets, the difference in preserved fat-free mass was about 0.43 kg5 — real, but not on its own a solution. Reviews of muscle preservation during weight loss consistently pair the two: adequate protein and resistance training, with resistance training the part that also maintains strength6.
The practical read: hit your protein target, and lift something heavy a couple of times a week. Neither substitutes for the other.
GLP-1 medications reduce appetite and slow gastric emptying. Total intake falls, meals get smaller and less predictable, and food often stops being interesting. Protein is the nutrient that suffers, because its target does not shrink along with your appetite — if anything, the guidance points the other way during active weight loss.
That is a tracking problem as much as a nutrition one. Full nutrition apps ask you to log everything, search databases and weigh portions, which is a lot of friction to apply to a 200-calorie meal you did not especially want.
GramsIn tracks one number. You text what you ate — “greek yogurt and two eggs” — and it replies with the protein and your running total for the day. No app to open, no database to search, no barcode to scan. For meals from major restaurant chains, it logs from each chain’s published nutrition data rather than estimating.
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You lose some, but the popular framing overstates it. In the STEP 1 semaglutide body-composition analysis, about 38% of the weight lost was lean body mass — and lean body mass is not the same thing as muscle. Because muscle is roughly half of lean body mass, the 2025 joint society advisory puts actual muscle loss at around 20% of total weight lost. In the peer-reviewed SURMOUNT-1 analysis of tirzepatide, about 25% of weight lost was lean mass, the same proportion seen in the placebo group. Losing some lean mass is a normal consequence of rapid weight loss of any kind, not something unique to these drugs.
The 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society states that targets of 1.2–1.6 grams of protein per kilogram of body weight per day “have also been proposed during active weight reduction.” It also notes that an absolute target of 80–120 grams per day may be easier to stick to. These are consensus recommendations from an expert panel, not a graded evidence guideline, and your clinician should set your actual target.
No. The 2025 joint society advisory is explicit: “increased protein intake alone is likely inadequate to support the preservation of muscle mass in the absence of structured resistance/strength training.” Protein and resistance training work together — in a meta-analysis of 24 randomized trials, higher protein intake by itself preserved about 0.43 kg of fat-free mass, a real but modest effect.
GLP-1 medications work partly by reducing appetite and slowing gastric emptying, so total food intake falls. When you are eating markedly less overall, protein is the nutrient most likely to fall short, because it is the one with a target that does not scale down with your appetite. That is why tracking it specifically — rather than tracking everything — is the practical approach for most people on these medications.
GramsIn is a protein tracker that works over text message. You text what you ate in plain language and it replies with the protein and your running daily total. There is no app to open and nothing to search, which matters when appetite is low and meals are small and frequent. For meals from major restaurant chains, GramsIn logs from each chain’s published nutrition data rather than estimating.
Every figure on this page is linked to the study it comes from, with the supporting text quoted so you can check it against the original. Evidence strength is labelled — a conference abstract is not the same as a peer-reviewed trial, and we say which is which.
Nutritional priorities to support GLP-1 therapy for obesity: A joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society
Mozaffarian D, Agarwal M, Aggarwal M, et al. · Obesity Pillars. 2025;15:100181
Joint society advisory
“Higher targets, such as 1.2–1.6 g/kg body weight/day, have also been proposed during active weight reduction.” The advisory also states that “increased protein intake alone is likely inadequate to support the preservation of muscle mass in the absence of structured resistance/strength training,” and that “setting an absolute protein target of 80–120 g/day may enhance adherence while ensuring adequate intake.”
doi:10.1016/j.obpill.2025.100181Impact of Semaglutide on Body Composition in Adults With Overweight or Obesity: Exploratory Analysis of the STEP 1 Study
Wilding JPH, Batterham RL, Calanna S, et al. · Journal of the Endocrine Society. 2021;5(Suppl 1):A16–A17
Conference abstract
“Total lean body mass decreased from baseline (-9.7%); however, the proportion relative to total body mass increased by 3.0%-points.” The 2025 joint advisory recalculates this as 8.3 kg (62%) fat and 5.3 kg (38%) lean body mass of the 13.6 kg lost.
doi:10.1210/jendso/bvab048.030Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight
Look M, Dunn JP, Kushner RF, et al. · Diabetes, Obesity and Metabolism. 2025;27(5):2720–2729
Peer-reviewed trial
Of the weight lost, “approximately 75% was fat mass and 25% was lean mass” — and that ratio was the same in the placebo group.
doi:10.1111/dom.16275Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies
Neeland IJ, Linge J, Birkenfeld AL. · Diabetes, Obesity and Metabolism. 2024;26(Suppl 4):16–27
Peer-reviewed review
“Reductions in lean mass range between 40% and 60% as a proportion of total weight lost, while other studies show lean mass reductions of approximately 15% or less of total weight lost.”
doi:10.1111/dom.15728Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials
Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. · American Journal of Clinical Nutrition. 2012;96(6):1281–1298
Meta-analysis
Across 24 randomized controlled trials (1,063 participants), higher-protein diets produced “mitigation of reductions in fat-free mass (FFM; 0.43 kg; 95% CI: 0.09, 0.78 kg).”
doi:10.3945/ajcn.112.044321Preserving Healthy Muscle during Weight Loss
Cava E, Yeat NC, Mittendorfer B. · Advances in Nutrition. 2017;8(3):511–519
Peer-reviewed review
“High protein intake helps preserve lean body and muscle mass during weight loss… both endurance- and resistance-type exercise help preserve muscle mass during weight loss, and resistance-type exercise also improves muscle strength.”
doi:10.3945/an.116.014506International Society of Sports Nutrition Position Stand: protein and exercise
Jäger R, Kerksick CM, Campbell BI, et al. · Journal of the International Society of Sports Nutrition. 2017;14:20
Position stand
“An overall daily protein intake in the range of 1.4–2.0 g protein/kg body weight/day is sufficient for most exercising individuals.” Note this position stand addresses exercising individuals, not people on obesity pharmacotherapy.
doi:10.1186/s12970-017-0177-8Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group
Bauer J, Biolo G, Cederholm T, et al. · Journal of the American Medical Directors Association. 2013;14(8):542–559
Position stand
Recommends “1.0 to 1.2 g protein per kilogram of body weight per day” for healthy adults over 65, and 1.2–1.5 g/kg/day for those with acute or chronic illness. Notes an exception for severe kidney disease.
doi:10.1016/j.jamda.2013.05.021Last reviewed 8 August 2026. Guidance in this area is moving quickly; if you are reading this long after that date, check whether newer recommendations exist.