Protein sources for athletes: animal, plant and alternative proteins

The question of "Which types of protein are best for athletes?" is no longer limited to which protein source produces the largest acute stimulation of muscle protein synthesis. In contemporary sports nutrition there is also a second question: "can protein choices that support recovery and adaptation also be more sustainable?"

This matters because diet is a major contributor to environmental impact. Estimates often place diet at roughly 20 to 30 percent of annual greenhouse gas emissions, with meat making a substantial contribution. At the same time, meat, dairy, eggs and cereal-based foods are important contributors to daily protein intake in many countries. Sports nutrition therefore has to consider two aims at the same time: supporting muscle reconditioning and recognising the wider implications of food choice.

Defining protein quality

The starting point is the definition of protein quality. Historically, protein quality was described in general nutrition terms as the ability of a protein source to meet the body's metabolic demands for amino acids and nitrogen. Later scoring systems, including PDCAAS and DIAAS, placed more emphasis on digestibility and the supply of indispensable amino acids.

In a sports nutrition context, the definition becomes more specific. The relevant question is whether a protein source can support the muscle-building process by stimulating muscle protein synthesis after ingestion. This definition is important because it shifts the discussion from simple protein quantity to the physiological factors that determine the anabolic potential of a food or supplement.

What determines the anabolic potential of a protein source?

Three factors are central. The first is digestion and absorption kinetics. This refers to both the proportion of protein-derived amino acids that become available in the circulation and the rate at which they appear. Whey protein is often described as a fast protein because its amino acids appear rapidly in the blood. Casein behaves differently because it clots in the stomach and releases amino acids more slowly.

The second factor is the essential amino acid profile and content. A protein source needs to provide all nine essential amino acids, and it must provide them in sufficient amounts. The third factor is leucine content. Leucine is important not only because it is incorporated into muscle protein, but also because it acts as a signal that helps activate the muscle protein synthetic machinery.

If amino acids are the bricks required to build a wall, then all the indispensable bricks must be available, and leucine acts both as a brick and as part of the signal that switches on the building process

These factors do not act independently. Digestibility, essential amino acid availability and leucine content interact to determine the postprandial muscle protein synthetic response. An analogy is useful: if amino acids are the bricks required to build a wall, then all the indispensable bricks must be available, and leucine acts both as a brick and as part of the signal that switches on the building process. If one essential amino acid is insufficient, the process may be constrained even when total protein intake appears adequate.

Why animal proteins often appear superior

This mechanistic framework explains why early comparisons between animal and plant proteins generally favoured animal proteins. Dairy proteins tend to have a high essential amino acid content and a high leucine content. Many single plant proteins, in contrast, are limited in at least one essential amino acid. Wheat is typically limited in lysine, whereas some legumes are relatively limited in methionine. Importantly, these limitations are not identical across plant sources, which becomes relevant when plant proteins are combined.

Several early studies supported the view that animal proteins were more anabolic. When skimmed milk was compared with soy milk after resistance exercise, muscle protein synthesis was greater with milk (1). Similar findings were reported when whey, casein and soy were compared, with whey producing the strongest stimulation of muscle protein synthesis (2). A comparison between micellar casein and wheat protein also favoured the animal protein source (3).

These findings were biologically plausible. The animal proteins in these studies generally provided higher digestibility, a more complete essential amino acid profile and greater leucine content. As a result, the working assumption in sports nutrition became that animal proteins were the preferred option when the goal was to maximise muscle protein synthesis during recovery.

The limitation of single plant protein comparison

The limitation of that conclusion is that many early studies compared animal proteins with isolated single plant proteins, such as soy or wheat. Such comparisons are informative, but they do not necessarily represent how plant-based diets can be constructed. A single plant protein may be limited by one indispensable amino acid, but another plant protein may provide more of that same amino acid.

This is the basis of complementary protein blending. If one plant source is relatively low in lysine and another is relatively low in methionine, combining the two can produce a more complete amino acid profile. The practical question is therefore not simply whether a single plant protein is inferior to whey or milk, but whether a well-designed plant protein blend can provide the amino acid profile required to stimulate muscle protein synthesis effectively.

Plant protein blends and muscle protein synthesis

More recent work has addressed this question directly. Studies have compared animal proteins with plant-derived protein blends rather than single isolated plant sources. Examples include blends of wheat, corn and pea protein; pea, brown rice and canola; and lysine-enriched wheat combined with chickpea (4, 5, 6). In these studies, the postprandial stimulation of muscle protein synthesis was not statistically different from the response observed with milk protein, whey protein or chicken.

Single plant proteins may produce a lower anabolic response than high-quality dairy proteins when compared directly and in isolation.

Longer-term tracer work provides a similar message. In one study using deuterium oxide methodology, free-living muscle protein synthesis was measured over ten days in older adults consuming either a carefully designed vegan diet or an omnivorous diet (7). The vegan diet included soy-based dairy alternatives, legumes, cereals, nuts, isolated pea protein and isolated rice protein, and was constructed to provide all essential amino acids across the day. Under these conditions, muscle protein synthesis did not differ between the vegan and omnivorous diets.

These findings do not mean that all proteins are equal on a gram-for-gram basis. Rather, they refine the conclusion. Single plant proteins may produce a lower anabolic response than high-quality dairy proteins when compared directly and in isolation. However, plant proteins can support a comparable response when they are combined in a way that provides sufficient essential amino acids and leucine.

From protein powders to meals and dietary patterns

This distinction is important for applied practice. Athletes do not consume amino acids in isolation; they consume foods, meals and dietary patterns. A meal containing complementary plant proteins can provide a high-quality amino acid profile even if each individual component is not complete on its own. Examples include meals that combine grains, legumes, nuts, seeds or pulses in ways that improve the total essential amino acid profile.

The implication is that protein quality should be considered at several levels: the isolated protein source, the meal, and the full day of intake. For athletes following vegetarian, vegan or more flexitarian diets, careful planning becomes important, but the evidence does not support the simple claim that plant-based strategies are unable to support muscle reconditioning.

Alternative protein sources

The discussion also extends beyond traditional animal and plant proteins. Alternative protein sources include fungal proteins such as mycoprotein, insect proteins such as mealworm protein, and microalgae. These sources are of interest because several have promising essential amino acid profiles and leucine contents.

Mycoprotein is among the best studied alternative sources. In studies comparing a mycoprotein-based vegan high-protein diet with an omnivorous high-protein diet, muscle protein synthesis rates were comparable, both at rest and after exercise. Insect protein has also shown promise. A study using mealworm protein reported a postprandial muscle protein synthetic response comparable to milk protein (8).

Microalgae represents another developing area. Some microalgae sources have relatively good digestibility, a substantial essential amino acid content and useful leucine content. In addition, certain algae may provide omega-3 fatty acids, which could have relevance for muscle metabolism. The evidence base is still emerging, but the mechanistic rationale for studying these sources is strong.

Summary

The overall conclusion is not that one protein source has now replaced another as the best choice for athletes. Protein quality remains important. Digestibility, essential amino acid profile, essential amino acid content and leucine content all influence the anabolic response. Dairy proteins, and whey in particular, remain highly effective options.

At the same time, the evidence has moved beyond a simple animal versus plant hierarchy. Plant protein sources can support muscle protein synthesis when they are combined to provide a complete essential amino acid profile. Alternative proteins may also become increasingly relevant as the evidence develops.

Future protein recommendations in sport should therefore be more holistic. They should continue to prioritise muscle reconditioning and performance, but they should also consider sustainability and the broader nutrient profile of the diet. If athletes reduce animal protein intake, attention should be paid to nutrients of concern as well as to total protein and amino acid quality.

The practical message is straightforward: protein source matters, but the answer is not simply animal or plant. The best strategy depends on the athlete, the goal, the total diet, the amino acid profile, practical food choices and, increasingly, sustainability.

References

1. Wilkinson SB, Tarnopolsky MA, MacDonald MJ, MacDonald JR, Armstrong D, Phillips SM. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr. 2007;85(4):1031-1040. doi:10.1093/ajcn/85.4.1031.

2. Tang JE, Moore DR, Kujbida GW, Tarnopolsky MA, Phillips SM. Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men. J Appl Physiol (1985). 2009;107(3):987-992. doi:10.1152/japplphysiol.00076.2009.

3. Gorissen SHM, Horstman AMH, Franssen R, Crombag JJR, Langer H, Bierau J, et al. Ingestion of Wheat Protein Increases In Vivo Muscle Protein Synthesis Rates in Healthy Older Men in a Randomized Trial. J Nutr. 2016;146(9):1651-1659. doi:10.3945/jn.116.231340.

4. Van Der Heijden INO, Monteyne AJ, West SAM, Morton JP, Langan-Evans C, Hearris MA, et al. Plant Protein Blend Ingestion Stimulates Postexercise Myofibrillar Protein Synthesis Rates Equivalently to Whey in Resistance-Trained Adults. Med Sci Sports Exerc. 2024;56(8):1467-1479. doi:10.1249/MSS.0000000000003432.

5. Kouw IWK, Pinckaers PJM, Le Bourgot C, van Kranenburg JMX, Zorenc AH, de Groot LCPGM, et al. Ingestion of an ample amount of meat substitute based on a lysine-enriched, plant-based protein blend stimulates postprandial muscle protein synthesis to a similar extent as an isonitrogenous amount of chicken in healthy, young men. Br J Nutr. 2022;128(10):1955-1965. doi:10.1017/S0007114521004906.

6. Pinckaers PJM, Kouw IWK, Gorissen SHM, Houben LHP, Senden JM, Wodzig WKHW, et al. The Muscle Protein Synthetic Response to the Ingestion of a Plant-Derived Protein Blend Does Not Differ from an Equivalent Amount of Milk Protein in Healthy Young Males. J Nutr. 2023;152(12):2734-2743. doi:10.1093/jn/nxac222.

7. Domić J, Pinckaers PJM, Grootswagers P, Siebelink E, Gerdessen JC, van Loon LJC, et al. A Well-Balanced Vegan Diet Does not Compromise Daily Mixed Muscle Protein Synthesis Rates when Compared with an Omnivorous Diet in Active Older Adults: A Randomized Controlled Cross-Over Trial. J Nutr. 2025;155(4):1141-1150. doi:10.1016/j.tjnut.2024.12.019.

8. Hermans WJH, Senden JM, Churchward-Venne TA, Paulussen KJM, Fuchs CJ, Smeets JSJ, et al. Insects are a viable protein source for human consumption: from insect protein digestion to postprandial muscle protein synthesis in vivo in humans: a double-blind randomized trial. Am J Clin Nutr. 2021;114(3):934-944. doi:10.1093/ajcn/nqab115.