Protein and muscle: what the science says
Protein contributes to the growth and maintenance of muscle mass, and exercise does most of the work. In an analysis of 49 studies, the benefit of extra protein stopped growing at around 1.6 g per kilogram of body weight a day. Your muscles carry the grocery bags, haul a tub of bell peppers up to the third floor for lyutenitsa (Bulgarian roasted pepper relish) and lift the suitcase into the trunk. Here you'll find out exactly what the EU says about protein and muscle, what one big analysis on the subject found, how much protein it makes sense to eat and why movement does most of the work.
In short
- Muscle makes up about 38% of body weight in men and about 31% in women (Janssen et al., 2000).
- The EU allows two claims about protein and muscle: protein contributes to a growth in muscle mass and to the maintenance of muscle mass.
- In an analysis of 49 studies with 1 863 people who did resistance training, extra protein added a little fat-free mass, and the benefit stopped growing at around 1.6 g per kilogram a day.
- Without resistance exercise, extra protein gave no statistically significant gain in muscle mass (a review of 74 studies, 2022).
- For someone who weighs 65 kg, 1.6 g/kg is about 104 g a day, and ordinary food can get you there.
Muscle on an ordinary day
Skeletal muscles are the ones you move at will: your legs, arms and back. In a study of 468 people aged 18 to 88, they made up about 38% of body weight in men and about 31% in women. That's quite a big organ, when you think about it.
The same study showed two more things. The gap between men and women is bigger in the upper body (about 40%) than in the legs (about 33%). And the visible drop in muscle mass starts around the late 40s and mostly affects the legs. More on this in Protein and age.
Muscle is a construction site that never closes. The body keeps breaking down some of its muscle protein and building new protein. The building work needs amino acids, and they come from the protein in food. Nine of them the body can't make on its own, so it has to get them from food. More on them in Complete protein and the 9 essential amino acids.
What the EU officially says
In the European Union, foods may only talk about effects on the body through authorized claims. The list is in Regulation (EU) No 432/2012, and it has three for protein:
- Protein contributes to a growth in muscle mass.
- Protein contributes to the maintenance of muscle mass.
- Protein contributes to the maintenance of normal bones.
The condition is that the food is at least a “source of protein” under EU rules. Behind the three claims are EFSA scientific opinions from 2010 and 2011.
Fact
If you see other promises about the body on the label of a protein product, compare them with these three sentences. They're the only ones on the EU's general list of authorized health claims for protein.
What the big 2018 analysis found
In 2018, Morton and colleagues pooled 49 randomized studies with a total of 1 863 healthy adults. All the participants did resistance exercise. One group got extra protein, the other didn't. The studies lasted about 13 weeks on average.
The results in numbers:
| What they measured | Difference with extra protein |
|---|---|
| Maximum weight lifted once | +2.49 kg |
| Fat-free mass | +0.30 kg |
| Daily protein above which the benefit stops growing | about 1.62 g per kilogram |
How should you read this? Extra protein helped, but modestly. About 300 g more fat-free mass in about three months is a small amount. The exercise itself does most of the work.
Two details are worth knowing. The 1.62 g figure has a wide margin of uncertainty, from 1.03 to 2.20 g per kilogram. And the effect got smaller with age and bigger in people with training experience.
Movement does most of the work
A newer review from 2022 pooled 74 randomized studies. More protein gave a small but clear gain in muscle mass when people did resistance exercise. Without that kind of exercise, the difference wasn't statistically significant.
The World Health Organization recommends that adults do muscle-strengthening exercise on at least 2 days a week, for all the major muscle groups. The gym is optional. Squats down to a chair, wall push-ups, a resistance band, taking the stairs, digging in the garden and carrying heavy bags all make your muscles work against resistance.
Myth
“Protein will make you bulky.” In the 2018 analysis, people who did resistance training for about 13 weeks gained, on average, about 300 g more fat-free mass from the protein. Muscle grows slowly, and only when you put it to work.
How much protein makes sense
For a healthy adult, the European Food Safety Authority (EFSA) gives 0.83 g per kilogram a day. The International Society of Sports Nutrition (ISSN) recommends 1.4 to 2.0 g per kilogram a day for building and maintaining muscle in most people who exercise regularly.
| Weight | EFSA (0.83 g/kg) | Around the plateau (1.6 g/kg) | ISSN (1.4 to 2.0 g/kg) |
|---|---|---|---|
| 55 kg | 46 g | 88 g | 77 to 110 g |
| 65 kg | 54 g | 104 g | 91 to 130 g |
| 80 kg | 66 g | 128 g | 112 to 160 g |
An interesting coincidence: the European Commission, drawing on EFSA data, considers an intake of up to twice the recommendation, about 1.7 g per kilogram, safe for healthy adults. The plateau from the analysis sits just below that limit. With kidney disease the rules are different, so ask your doctor.
How you spread your protein matters too. The ISSN advises 20 to 40 g at a time, every 3 to 4 hours. The details are in How to spread your protein through the day. If you're over 65, also see Protein and age.
What 104 g looks like as food
The ISSN writes that active people can meet their needs with ordinary food. Here's a day for an active person who weighs 65 kg. The numbers are calculated from USDA FoodData Central, the US public database of food composition:
- Breakfast. Three scrambled eggs, 50 g of Bulgarian white cheese and a slice of bread: about 28.6 g.
- Lunch. 200 g of beans, two slices of bread and 150 g of strained yogurt: about 38.1 g.
- Afternoon. 150 g of cottage cheese: about 16.7 g.
- Dinner. 200 g of pasta with 50 g of white cheese: about 18.7 g.
That's about 102 g in total, a step away from the target. Dinner is the lightest meal of this day. If you want more protein at dinner without changing the recipe, 1 serving (30 g) of MEALUP sprinkled over the pasta adds at least 20 g of protein from egg white and milk protein.
Frequently asked questions
Do I need protein powder to build muscle?
The ISSN writes that active people can meet their needs with ordinary food, and powders are a practical way to add protein. We cover what's in them in our article on whether protein powder is just chemicals.
If I don't work out, is protein worth thinking about?
Yes. Protein contributes to the maintenance of muscle mass, and you need that muscle every day. To build more muscle, though, you also need resistance exercise.
Is more than 2 g per kilogram better?
In the 2018 analysis, the benefit for fat-free mass stopped growing at around 1.6 g per kilogram. Above that figure, a higher intake added nothing more.
Does it matter when I eat my protein?
Scientists are still working out the full answer. In a small 2014 study, protein spread evenly across three meals gave 25% more muscle protein synthesis over 24 hours than a day with almost all of it at dinner. How to do this with ordinary food is in How to spread your protein through the day.
Does plant protein do the same job?
Plant proteins also bring amino acids for your muscles, but their makeup is different. Details in Animal vs plant protein.
Does a lot of protein harm the kidneys?
For healthy adults, an intake of up to about 1.7 g per kilogram is considered safe. If you have kidney disease, ask your doctor. More in Protein myths.
Carry the bags, take the stairs, squat down to the chair and put protein on your plate. Your muscles will do the rest.
Sources
- Janssen I., Heymsfield S. B., Wang Z. M., Ross R., “Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr”, Journal of Applied Physiology, 2000
- Commission Regulation (EU) No 432/2012 of 16 May 2012, Annex: list of permitted health claims (text as adopted)
- Morton R. W., Murphy K. T., McKellar S. R. et al., “A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults”, British Journal of Sports Medicine, 2018
- Nunes E. A., Colenso-Semple L., McKellar S. R. et al., “Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults”, Journal of Cachexia, Sarcopenia and Muscle, 2022
- Bull F. C., Al-Ansari S. S., Biddle S. et al., “World Health Organization 2020 guidelines on physical activity and sedentary behaviour”, British Journal of Sports Medicine, 2020
- EFSA, “EFSA sets population reference intakes for protein”, press release, 2012
- European Commission, Knowledge for Policy, “Dietary recommendations for protein intake for adults and older adults”, 2026
- Jäger R., Kerksick C. M., Campbell B. I. et al., “International Society of Sports Nutrition Position Stand: protein and exercise”, Journal of the International Society of Sports Nutrition, 2017
- Mamerow M. M., Mettler J. A., English K. L. et al., “Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults”, The Journal of Nutrition, 2014
- USDA, FoodData Central: egg 171287, feta 173420, white bread 174924, white beans 175203, strained yogurt 171304, cottage cheese 172179, pasta 169737
