What research says about protein for people taking a GLP-1 medication
If you take a GLP-1 medication, you may have read that some of the weight you lose is muscle, not fat.
Does a GLP-1 medication cause muscle loss?
In the STEP 1 trial, people taking a GLP-1 medication lost 13.6 kg on average. About 38% of that was lean body mass, and the 2025 advisory estimates roughly half of that, about 20% of total weight lost, was muscle specifically.
Lean body mass includes muscle along with other non-fat tissue, so the 38% figure is not the same as the muscle figure (Mozaffarian et al., Obesity, 2025, citing the STEP 1 trial, New England Journal of Medicine, 2021). Separate modeling research not specific to GLP-1 medications estimates that when people lose weight through calorie reduction alone, muscle makes up roughly 20 to 26% of weight lost in men and 10 to 17% in women, when there is no structured strength training (Heymsfield et al., Obesity, 2024). The same 2025 advisory states that protein intake alone is unlikely to protect muscle without structured resistance or strength training.
This is general research on GLP-1 medications and weight loss. It is not research on L-Protein.
About L-Protein
L-Protein is a plant-based protein powder from Prolon. It has all nine essential amino acids, with added L-methionine, an amino acid plant proteins often provide in smaller amounts. L-Protein supports your daily protein intake and comes in Chocolate and Berry flavors.
Before you start
L-Protein is a food, not a medication. It is not a substitute for any treatment your healthcare practitioner has prescribed. If you take a GLP-1 medication, talk with your healthcare practitioner about how much protein is right for you.