Does animal protein really build more muscle than plant protein?
Do muscles respond differently to protein depending on where it comes from? In this series, we take a critical look at widespread myths. This time: the source of your protein.
Muscle makes up around 40% of total body mass and contains roughly 50–75% of all the body’s proteins. It consists of approximately 75% water, 20% protein and around 5% carbohydrates, mineral salts and fatty acids [1]. Proteins play a major role in the development of strength, as they form the basic structural units of muscle tissue in the form of sarcomeres. Muscle mass is regulated by the continuous synthesis and breakdown of proteins [2]. When muscle protein synthesis (MPS) exceeds muscle protein breakdown (MPB), muscle mass increases. In the reverse scenario – where MPB exceeds MPS – we lose muscle mass.
Maintaining muscle mass is supported by adequate dietary protein intake, as this promotes MPS [3–5].
The effect of strength training on protein balance
Phillips et al. [6] showed that a single strength training session – consisting of concentric or eccentric leg extension movements performed in 8 sets of 8 repetitions at 80% of 1-RM – significantly increased both MPS and MPB in 8 untrained individuals (4 men, 4 women). While protein breakdown returned to baseline within 48 hours, protein synthesis remained significantly elevated (p < 0.01). In addition, the increase in MPS was more pronounced than that of MPB. The result? A positive net protein balance. Strength training therefore strongly stimulates both processes, with MPS showing greater duration and magnitude. Combined with a sufficient daily protein intake of around 1.6–2.2 g/kg body weight, this creates a positive net protein balance that optimally supports muscle growth [7–9].
Animal or plant protein: which is better for muscle gain?
For proteins to reach the muscles, they must first be consumed, digested and distributed throughout the body. At rest, the gut and liver use around 50% of ingested protein for their own metabolic processes. Of the remaining 50%, around 40% is used elsewhere, while only approximately 10% of the originally ingested protein is actually available for muscle protein synthesis [9].
Studies using amino acid tracer methods show that a protein source’s ability to stimulate muscle building depends on how well the protein is digested, how quickly the amino acids are absorbed and which essential amino acids it contains [10–16]. The essential amino acid leucine is particularly important in this context [17]. Essential amino acids are building blocks of proteins that the body can’t produce on its own and must therefore obtain through food.
Digestibility: a difference between animal and plant proteins
Plant protein sources have lower digestibility than animal proteins [18]. Digestibility refers to the proportion of ingested amino acids that’s actually digested and absorbed, and therefore available for the body’s own protein synthesis [19]. Animal proteins such as dairy products, eggs and meat have a very high digestibility of over 90% [18]. For plant proteins, digestibility can be further reduced depending on the processing method [19] and the presence of substances that inhibit nutrient absorption or impair their use in the body. It typically falls between 45% and 80% [18]. When these inhibiting substances are removed, however, plant protein sources such as soy protein isolate, pea protein concentrate and wheat gluten show digestibility comparable to that of animal proteins (>90%) [18].
Of the essential amino acids, leucine is considered the most important for stimulating MPS after a meal [17]. For this reason, the leucine content is considered a significant, independent factor in the protein source’s ability to stimulate MPS [17,20,21]. Animal proteins generally contain more leucine than plant proteins. Whey protein has a leucine content of around 13.6%, while most plant sources reach only 6–8% [22].
In other words, animal and plant protein sources differ in terms of their amino acid composition and digestibility.
Plant vs. animal: which leads to more muscle growth?
A recently published randomised clinical trial investigated this question [23]. In the study, 44 untrained young men (aged 18–35) received either a plant-based protein supplement (soy and pea protein) or whey protein as a dietary supplement, combined with strength training three times a week for 12 weeks. Both groups consumed 45 g of protein per day (3 × 15 g) in addition to their main meals. As expected, both groups showed comparable gains in muscle mass and strength, with no significant difference observed between the groups (p > 0.05). No long-term differences in muscle mass or strength were observed, because the leucine content and amino acid profile were similar in both groups. Combining multiple plant proteins compensates for the suboptimal amino acid profile of any single plant protein compared to whey. Systematic reviews and meta-analyses paint a similar picture [24, 25]: protein source has no effect on muscle mass or strength.
To sum up, if the amino acid profile of the plant and animal protein source is similar, no differences in muscle mass or strength are expected when combined with strength training.
References
- Frontera WR, Ochala J. Skeletal Muscle: A Brief Review of Structure and Function. Calcif Tissue Int. 2015;96: 183–195. doi:10.1007/s00223-014-9915-y
- Phillip SM. Physiologic and molecular bases of muscle hypertrophy and atrophy: Impact of resistance exercise on human skeletal muscle (protein and exercise dose effects). Appl Physiol Nutr Metab. 2009;34: 403–410. doi:10.1139/H09-042
- Bennet WM, Connacher AA, Scrimgeour CM, Smith K, Rennie MJ. Increase in anterior tibialis muscle protein synthesis in healthy man during mixed amino acid infusion: Studies of incorporation of [1-13C]leucine. Clin Sci. 1989;76: 447–454. doi:10.1042/cs0760447
- Bohé J, Aili Low JF, Wolfe RR, Rennie MJ. Latency and duration of stimulation of human muscle protein synthesis during continuous infusion of amino acids. J Physiol. 2001;532: 575–579. doi:10.1111/j.1469-7793.2001.0575f.x
- Fujita S, Dreyer HC, Drummond MJ, Glynn EL, Cadenas JG, Yoshizawa F, et al. Nutrient signalling in the regulation of human muscle protein synthesis. J Physiol. 2007;582: 813–823. doi:10.1113/jphysiol.2007.134593
- Phillips SM, Tipton KD, Aarsland A, Wolf SE, Wolfe RR. Mixed muscle protein synthesis and breakdown after resistance exercise in humans. https://doi.org/101152/ajpendo19972731E99. 1997;273. doi:10.1152/AJPENDO.1997.273.1.E99
- Lemon PWR, Tarnopolsky MA, MacDougall JD, Atkinson SA. Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders. J Appl Physiol. 1992;73: 767–775. doi:10.1152/jappl.1992.73.2.767
- Tarnopolsky MA, Atkinson SA, MacDougall JD, Chesley A, Phillips S, Schwarcz HP. Evaluation of protein requirements for trained strength athletes. J Appl Physiol. 1992;73: 1986–1995. doi:10.1152/jappl.1992.73.5.1986
- Stokes T, Hector AJ, Morton RW, McGlory C, Phillips SM. Recent perspectives regarding the role of dietary protein for the promotion of muscle hypertrophy with resistance exercise training. Nutrients. 2018;10. doi:10.3390/nu10020180
- Pennings B, Boirie Y, Senden JMG, Gijsen AP, Kuipers H, Loon LJC Van. Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. 2011; 997–1005. doi:10.3945/ajcn.110.008102.1
- Koopman R, Walrand S, Beelen M, Gijsen AP, Kies AK, Boirie Y, et al. Dietary Protein Digestion and Absorption Rates and the Subsequent Postprandial Muscle Protein Synthetic Response Do Not Differ between Young and Elderly Men,. J Nutr. 2009;139: 1707–1713. doi:10.3945/JN.109.109173
- Burd NA, Pennings B, Groen BBL, Gijsen AP, Senden JMG, Van Loon LJC. The single biopsy approach is reliable for the measurement of muscle protein synthesis rates in vivo in older men. J Appl Physiol. 2012;113: 896–902. doi:10.1152/JAPPLPHYSIOL.00513.2012/ASSET/IMAGES/LARGE/ZDG0181202870005.JPEG
- Koopman R, Crombach N, Gijsen AP, Walrand S, Fauquant J, Kies AK, et al. Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein. Am J Clin Nutr. 2009;90: 106–115. doi:10.3945/AJCN.2009.27474
- Pennings B, Pellikaan WF, Senden JMG, van Vuuren AM, Sikkema J, Van Loon LJC. The production of intrinsically labeled milk and meat protein is feasible and provides functional tools for human nutrition research. J Dairy Sci. 2011;94: 4366–4373. doi:10.3168/jds.2011-4451
- Volpi E, Kobayashi H, Sheffield-Moore M, Mittendorfer B, Wolfe RR. Essential amino acids are primarily responsible for the amino acid stimulation of muscle protein anabolism in healthy elderly adults. Am J Clin Nutr. 2003;78: 250. doi:10.1093/AJCN/78.2.250
- Tipton KD, Gurkin BE, Matin S, Wolfe RR. Nonessential amino acids are not necessary to stimulate net muscle protein synthesis in healthy volunteers. J Nutr Biochem. 1999;10: 89–95. doi:10.1016/S0955-2863(98)00087-4
- Van Loon LJC. Leucine as a pharmaconutrient in health and disease. Curr Opin Clin Nutr Metab Care. 2012;15: 71–77. doi:10.1097/MCO.0b013e32834d617a
- Gilani S, Tomé D, Moughan P, Burlingame B. Report of a Sub-Committee of the 2011 FAO Consultation on “ Protein Quality Evaluation in Human Nutrition ” on: The assessment of amino acid digestibility in foods for humans and including a collation of published ileal amino acid digestibility data for. FAO Expert. 2012;2012: 58. Available: http://www.fao.org/ag/humannutrition/36216-04a2f02ec02eafd4f457dd2c9851b4c45.pdf
- Rutherfurd SM, Moughan PJ. Available versus digestible dietary amino acids. Br J Nutr. 2012;108: S298–S305. doi:10.1017/S0007114512002528
- Garlick PJ. The Role of Leucine in the Regulation of Protein Metabolism. J Nutr. 2005;135: 1553S-1556S. doi:10.1093/JN/135.6.1553S
- Millward DJ, Layman DK, Tomé D, Schaafsma G. Protein quality assessment: impact of expanding understanding of protein and amino acid needs for optimal health. Am J Clin Nutr. 2008;87: 1576S-1581S. doi:10.1093/AJCN/87.5.1576S
- Stokes T, Hector AJ, Morton RW, McGlory C, Phillips SM. Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients. 2018;10. doi:10.3390/NU10020180
- Santini MH, Erwig Leitão A, Mazzolani BC, Smaira FI, de Souza MSC, Santamaria A, et al. Similar effects between animal-based and plant-based protein blend as complementary dietary protein on muscle adaptations to resistance training: findings from a randomized clinical trial. J Int Soc Sports Nutr. 2025;22: 2568047. doi:10.1080/15502783.2025.2568047
- Lim MT, Pan BJ, Toh DWK, Sutanto CN, Kim JE. Animal Protein versus Plant Protein in Supporting Lean Mass and Muscle Strength: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutr 2021, Vol 13, Page 661. 2021;13: 661. doi:10.3390/NU13020661
- Messina M, Lynch H, Dickinson JM, Reed KE. No difference between the effects of supplementing with soy protein versus animal protein on gains in muscle mass and strength in response to resistance exercise. Int J Sport Nutr Exerc Metab. 2018;28: 674–685. doi:10.1123/ijsnem.2018-0071
Molecular and Muscular Biologist. Researcher at ETH Zurich. Strength athlete.
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