How much protein do you need on a GLP-1? What the research says about protecting muscle

Why protein comes up so often with GLP-1s

When you lose weight by eating less, with or without medication, you lose some lean mass along with fat. Lean mass is everything that is not fat: muscle, but also water, organs and bone. Losing some is expected. Losing more than necessary is worth avoiding, because muscle helps with strength, balance and blood-sugar control, especially as we age.

GLP-1 medicines make people feel full sooner and for longer. That is how they work, but it also means meals get smaller, and protein can quietly drop well below what people ate before.

What the trials measured

Both landmark trials scanned a subset of participants with DXA, an X-ray method that separates fat from lean mass.

STEP 1 (semaglutide). Among 140 people who were scanned, the average weight loss was 13.6 kg, of which 8.3 kg (62%) was fat and 5.3 kg (38%) was lean mass, as summarised in the 2025 advisory.^1,3

SURMOUNT-1 (tirzepatide). In 160 scanned participants, people on tirzepatide lost 33.9% of their fat mass and 10.9% of their lean mass, vs 8.2% and 2.6% on placebo. About 74% of the weight lost was fat and 26% lean, a split very similar to the placebo group's 75% and 25%.²

How much protein does the research suggest?

The clearest guidance so far is a 2025 joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society.¹ It does not set a single number. Instead it lays out the options:

• The standard adult allowance is 0.8 g per kg of body weight per day.
• Higher targets of 1.2–1.6 g per kg per day have been proposed during active weight loss.
• It is not settled which body weight to use: actual weight, an adjusted or ideal weight, or lean mass. For people with a lot of weight to lose, using current weight gives very high numbers.
• An absolute target of 80–120 g a day (about 16–24% of calories on a 2,000 kcal diet) may be simpler to follow.
• Avoid going below about 0.4–0.5 g/kg a day, and avoid staying at 2 g/kg a day or more over the long term.

Protein alone is not the whole answer

The advisory is direct about this: higher protein "is likely inadequate" to preserve muscle without structured strength training. It recommends pairing GLP-1 treatment with strength training at least three times a week, plus at least 150 minutes of moderate aerobic activity weekly.¹ That can be as simple as bodyweight squats, resistance bands or machines at a gym.

Making it work when you are not hungry

• Protein first. Eat the protein part of the meal before the rest, while appetite is still there.
• Spread it out. Three or four smaller servings are easier than one big one. A typical serving of 25–30 g is a palm-sized portion of chicken or fish, a cup of Greek yogurt, or three eggs plus a glass of milk.
• Use dense options. Greek yogurt, cottage cheese, eggs, tofu, lentils, fish, lean meat and milk give a lot of protein for a small volume.
• Drink enough. Lower food intake also means less water from food. Dehydration can make nausea and constipation worse.
• Track for a couple of weeks. Most people overestimate how much protein they eat. A short period of logging shows where you really are.