Protein and Muscle on GLP-1 Medication
What the trials found about lean mass, and the two things that protect it: enough protein, and lifting.
The honest version of the muscle question
"GLP-1s make you lose muscle" is the loudest claim in this space, and it is half right in a way that matters.
Gold· human data In the body-composition substudy of SURMOUNT-1, people on tirzepatide lost about 21% of their body weight over 72 weeks, of which roughly 74% was fat and 26% lean tissue. The striking part is the comparison: the placebo group's split was essentially the same. In the STEP 1 substudy semaglutide reduced total fat mass by about 19% and lean mass by about 10%, and because fat fell faster than lean, the proportion of the body that was lean tissue went up.
So the drugs are not unusually unkind to muscle. Large, fast weight loss is unkind to muscle, and these drugs produce large, fast weight loss. That is a better way to hold the problem, because it points at the answer: the loss is proportional to how much and how fast you lose, and it is modifiable.
Lean mass is not all muscle
One nuance the headlines drop. "Lean mass" on a DXA scan includes water, glycogen and the mass of the gut and organs, all of which shrink when you eat much less. A drop in lean mass is therefore not a one-for-one reading of lost muscle, and some of it comes back when intake stabilises. It is still worth defending, just not worth panicking about.
The two things that work
Protein, every day. Around 1.2 to 1.6 g per kg of body weight is the range expert guidance converges on for weight loss on these medicines, and towards or above the top of it if you are training seriously. Get your figure from the protein intake calculator, then split it across four or five small feeds, because a single large protein meal is exactly the meal you can no longer finish. If you cannot reach the number with food, a shake is the pragmatic fix.
Resistance training, two to three times a week. This is the half people skip, and protein without it slows lean-mass loss rather than preventing it. Two or three full-body sessions a week is enough; progressive overload matters more than the split. The training volume calculator and the exercise library will get you a plan that fits.
Track something other than the scale
The scale cannot tell you what you lost. Track a lift you can measure, a waist measurement, and how you look in a photograph every month. If strength is holding and the waist is shrinking, the composition of the loss is fine. If strength is falling off a cliff, that is the signal to eat more protein and train, not to weigh yourself more often.
For a rough baseline of where you stand, the lean body mass calculator and the FFMI calculator turn a weight and a body-fat estimate into numbers you can re-check in three months.
Supplements, briefly
A protein powder is a delivery mechanism for a target you cannot eat your way to, which on these drugs is a real constraint rather than a marketing one. Creatine monohydrate is the best-evidenced supplement for supporting training performance and lean mass, and it is cheap. Neither one substitutes for the training, and no supplement compensates for under-eating protein for six months.
The picks below
The tables that follow are the protein-dense and calorie-dense ends of the food reference dataset: the foods that put the most protein into the smallest volume, and the ones to lean on when you cannot finish a meal at all.
Protein first, every meal
The single highest-value habit on these drugs: eat the protein on the plate before anything else, because you may not reach the rest of it. These are the densest sources in a small portion.
| Food | Typical portion | Protein (g) | Calories (kcal) | Why it earns the space |
|---|---|---|---|---|
| Greek yoghurt (low-fat) | 1 pot (170 g) | 17 | 100 | Soft, cold and high in protein per spoonful, and usually tolerated on the days when nothing else appeals. |
| Chicken breast (cooked) | 1 breast (120 g) | 37 | 198 | The most protein per gram of any everyday food here; keep it moist (poached, in a sauce) as dry meat is hard work on a slow stomach. |
| Cod (cooked) | 1 fillet (140 g) | 32 | 147 | Lean, low-fat and light, so it leaves the stomach faster than red meat or anything fried. |
| Egg (whole) | 1 large egg (50 g) | 7 | 78 | Small, soft, cheap and complete; scrambled eggs are a reliable meal when appetite has vanished. |
| Cottage cheese | 1 serving (100 g) | 11 | 98 | High protein, no cooking, and easy to eat in the small amounts that actually get finished. |
| Firm tofu | 1/2 block (150 g) | 18 | 180 | The densest plant protein in this dataset per calorie, and it takes on whatever flavour still tastes right to you. |
| Tuna, canned in water | 1 small tin (100 g) | 26 | 116 | Store-cupboard protein with almost no fat, for days when cooking is beyond you. |
| Prawns (cooked) | 1 serving (100 g) | 24 | 99 | Very lean, quick to eat, and light enough not to sit heavily. |
When you cannot finish a meal
Some weeks the problem is the opposite one: you cannot eat enough to hit your protein target or your micronutrients. These pack the most into the fewest mouthfuls. Use them deliberately, not by default.
| Food | Typical portion | Protein (g) | Calories (kcal) | Why it earns the space |
|---|---|---|---|---|
| Peanut butter | 1 tbsp (16 g) | 4 | 94 | Protein and calories in a tablespoon; stir it into porridge or yoghurt rather than eating a fatty meal. |
| Cheddar cheese | 1 matchbox (30 g) | 8 | 121 | A matchbox piece is real protein, useful when a whole meal is not happening. |
| Almonds | 1 handful (28 g) | 6 | 162 | A handful is protein, fibre, vitamin E and magnesium, which matters when total intake is low. |
| Pumpkin seeds | 1 handful (28 g) | 8 | 157 | The most protein-dense seed here, and easy to scatter over food you are already eating. |
| Whole milk | 1 glass (200 g) | 7 | 122 | Drinkable calories and protein for the days when chewing is the barrier. |
| Avocado | 1/2 avocado (100 g) | 2 | 160 | Calorie-dense and soft, though the fat load means it suits the settled days better than the nauseous ones. |
Protein and calorie figures are for the typical portion shown, from the same approximate food-composition dataset as the food reference tables.
Sources
- Wilding JPH, et al. Impact of semaglutide on body composition: exploratory analysis of STEP 1. J Endocr Soc 2021
- Look M, et al. Body composition changes during weight reduction with tirzepatide in SURMOUNT-1. Diabetes Obes Metab 2025
- Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from ACLM, ASN, OMA and TOS. Am J Clin Nutr 2025
- Nutritional and lifestyle supportive care recommendations for management of obesity with GLP-1-based therapies: expert consensus (modified Delphi), 2025
Work out your numbers
Frequently asked questions
- Do GLP-1 drugs make you lose muscle?
- They cause large, fast weight loss, and large fast weight loss always includes lean tissue. In the SURMOUNT-1 body-composition substudy about 26% of the weight lost was lean mass, essentially the same proportion as in the placebo group, so the driver is the size of the loss rather than something unique to the drug.
- How much protein should I aim for?
- Broadly 1.2 to 1.6 g per kg of body weight a day for weight loss on these drugs, and towards the higher end, or above it, if you are resistance training. Calculate your own number, then plan meals around it rather than hoping to reach it.
- Is protein alone enough to keep muscle?
- No. Protein without a training stimulus slows lean-mass loss but does not stop it. Resistance training two to three times a week is the other half, and it is the half people skip.
- Should I take creatine or a protein powder?
- A protein powder is a practical way to hit a target you physically cannot eat your way to; creatine monohydrate is the best-evidenced supplement for supporting training performance and lean mass. Neither substitutes for the training itself.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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