FormaGet FormaOn a GLP-1, protein and lifting protect what you keep.
GLP-1 medications such as semaglutide and tirzepatide produce large weight loss in trials. Part of that loss can be lean mass. A 2025 joint advisory from four obesity and nutrition societies puts protein and strength training at the center of the plan.
Published and last reviewed October 13, 2026 · 7-minute read
Published by Forma · Editorial responsibility: Aymane Belarbi, founder
This is not medical advice
This guide summarizes published research for general information. GLP-1 medications are prescription drugs. Your prescriber, a registered dietitian, or another qualified clinician should set your protein target, training plan, and any changes to them, especially if you have kidney disease or another medical condition.
What the main trials showed
| Trial | Medication and length | Mean weight change |
|---|---|---|
| STEP 1 (1,961 adults without diabetes) | Semaglutide 2.4 mg once weekly plus lifestyle intervention, 68 weeks | -14.9% with semaglutide vs -2.4% with placebo |
| SURMOUNT-1 (2,539 adults without diabetes) | Tirzepatide 5, 10 or 15 mg once weekly, 72 weeks | -15.0%, -19.5% and -20.9% by dose vs -3.1% with placebo |
Results are trial averages. Individual responses vary, and the most common side effects in both trials were gastrointestinal.
Why lean mass matters
A 2025 meta-analysis pooled 36 randomized controlled trials with 2,555 participants. GLP-1 receptor agonists clearly reduced fat mass, body fat percentage, and visceral fat. Compared with placebo they also reduced lean mass, while the lean mass percentage did not differ. The authors note that lean mass loss appeared in most studies and was more pronounced in people with overweight or obesity and with longer treatment.
The advisory explains why that matters: low muscle and bone mass are linked to physical impairment, falls and fractures, and reduced quality of life. It names preserving muscle and bone mass through resistance training and appropriate diet as a priority during GLP-1 use.
Protein: the numbers in the advisory
| Reference point | What the advisory says |
|---|---|
| General adult RDA | 0.8 g/kg per day, currently under review. |
| During active weight reduction | Higher targets of 1.2 to 1.6 g/kg per day have been proposed. |
| Based on lean mass | 1.5 g per kg of fat-free mass per day is considered more accurate but needs body composition data. |
| Simple absolute target | 80 to 120 g per day may improve adherence while ensuring adequate intake. |
| Limits | Intake should not fall below 0.4 to 0.5 g/kg per day; prolonged intake at or above 2 g/kg per day should be avoided. |
For people with obesity, the advisory says it is unclear whether targets should use actual, adjusted, or ideal body weight, because actual weight can overestimate protein needs.
Appetite is often lower on a GLP-1, so the advisory suggests eating protein-rich foods first in a meal to make sufficient intake more likely.
Training: protein is not enough on its own
Strength training
The advisory recommends prescribing GLP-1s together with a structured exercise program, aiming for strength training at least 3 times weekly, customized to fitness level and physical capacity.
Aerobic activity
It adds at least 150 minutes of moderate-intensity aerobic exercise per week, and notes that aerobic activity alone has a smaller effect on preserving lean mass during rapid weight reduction.
What to track each week
Protein
Daily grams against the target your clinician set, since appetite can make it easy to fall short.
Strength
Sets, reps, and load on your main lifts, so you can see whether strength holds while weight drops.
Weight trend
A smoothed bodyweight trend rather than single weigh-ins, to judge the rate of loss.
Total intake
Calories and macros, so very low intake on low-appetite days is visible.
Which apps help
| App | GLP-1 medication features | Protein and macros | Strength training log |
|---|---|---|---|
| Forma | Does not log medication | Yes | Yes: sets, reps, load, progressive overload |
| MyFitnessPal | GLP-1 journey support: log doses and set reminders | Yes | Logs workouts and steps |
| Lose It! | Log medication and view estimated GLP-1 levels | Yes | Logs exercise |
Disclosure: Forma publishes this guide. MyFitnessPal and Lose It! features are taken from their U.S. App Store listings, checked October 13, 2026. See the full weight and calorie app comparison.
Frequently asked questions
How much protein should I eat on a GLP-1?
A 2025 joint advisory notes that targets of 1.2 to 1.6 g/kg per day have been proposed during active weight reduction, and that an absolute target of 80 to 120 g per day may be easier to follow. Your prescriber or dietitian should set your own target.
Is protein enough to keep muscle on a GLP-1?
The advisory says increased protein alone is likely inadequate to preserve muscle mass without structured resistance training. It recommends regular strength training at least 3 times weekly plus at least 150 minutes of moderate aerobic exercise.
Do GLP-1 medications cause muscle loss?
A 2025 meta-analysis of 36 randomized trials found that GLP-1 receptor agonists reduced fat mass and, compared with placebo, reduced lean mass, with no difference in lean mass percentage.
What is the best app to track macros and workouts on a GLP-1?
If you want to log doses, MyFitnessPal and Lose It! list GLP-1 medication features. If you want protein, macros, strength training and weight trend in one app, Forma tracks those together but does not log medication.
Primary references
New England Journal of Medicine, 2021 (STEP 1). PMID: 33567185.
New England Journal of Medicine, 2022 (SURMOUNT-1). PMID: 35658024.
European Journal of Pharmacology, 2025. 36 trials, 2,555 participants. PMID: 40615102.
American Journal of Clinical Nutrition, 2025. Joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. PMID: 40450457.
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