Plant Protein vs. Animal Protein — What the Research Actually Shows

The quality gap is real. But it’s bridgeable — if you know where to look.

Not all protein is created equal, and the difference largely comes down to essential amino acid profiles. van Vliet et al. (2015) published a comprehensive review in the Journal of Nutrition comparing plant-based and animal-based protein sources for skeletal muscle anabolism and concluded that plant proteins generally have lower EAA content, lower leucine content, and lower digestibility than animal proteins.

The specifics matter. Most grains are limiting in lysine. Most legumes are limiting in methionine. No single plant protein source provides the complete EAA profile at concentrations that match whey, egg, or meat. Gorissen et al. (2018) analyzed the amino acid composition of commercially available plant-based protein isolates in Amino Acids and found that leucine content ranged from 6.8% (hemp) to 8.2% (brown rice) — compared to 10.9% for whey protein isolate.

By the DIAAS scoring system, Rutherfurd et al. (2015) showed in the British Journal of Nutrition that whey protein concentrate scores 1.09, whole milk powder 1.14, and soy protein isolate 0.90 — while wheat scores 0.40 and rice scores 0.37 (truncated to 1.0 as the maximum).

What this means practically

For plant-based eaters, the strategies to optimize MPS are: combine complementary plant proteins to cover limiting amino acids, consume higher total protein quantities to compensate for lower EAA density, and consider EAA supplementation to fill the specific gaps.

An EAA supplement is, by definition, a complete essential amino acid source regardless of its origin — the amino acids are the same whether derived from plant or animal precursors. EAA supplementation effectively levels the playing field for plant-based dieters without requiring them to eat impractical volumes of food.

References

1. van Vliet S, Burd NA, van Loon LJC. The skeletal muscle anabolic response to plant- versus animal-based protein consumption. J Nutr. 2015;145(9):1981-1991. PubMed
2. Gorissen SHM, Crombag JJR, Senden JMG, et al. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids. 2018;50(12):1685-1695. PubMed
3. Rutherfurd SM, Fanning AC, Miller BJ, Moughan PJ. Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats. J Nutr. 2015;145(2):372-379. PubMed