Whey vs plant protein, by the evidence
Whey wins per gram on completeness, leucine, and digestibility, but soy and blended plant proteins close most of the gap at a higher dose. What separates them, when it matters, and how to choose.
What people ask us next.
- Is whey or plant protein better for building muscle?
- Per gram, whey, because it is complete, scores highest on the DIAAS quality scale, and is richest in leucine, the amino acid that triggers muscle growth (Moore et al. 2015). But the gap is a dose problem, not a wall. Soy is a complete plant protein, and pea-rice blends fix the missing amino acids, so at a slightly larger serving plant protein drives comparable gains when total daily protein is adequate (Morton et al. 2018). Choose based on diet, tolerance, and cost.
- Why is whey considered higher quality than plant protein?
- Two reasons. First, completeness: whey supplies all nine essential amino acids in usable ratios and scores at the top of the DIAAS scale, while most single plant proteins are low in one, rice in lysine, pea in methionine (Gorissen et al. 2018). Second, leucine: whey is about 11% leucine versus roughly 7-8% for pea or rice, so it hits the muscle-building threshold in a smaller dose. Soy is the plant exception that matches animal protein on completeness.
- Can I build the same muscle on plant protein?
- Yes, with two adjustments. Use complete or blended sources (soy, or a pea-rice blend) so you are not short an essential amino acid, and take a slightly larger dose to match whey's leucine. Controlled studies show animal protein edges plant per gram acutely, but full training trials show comparable muscle and strength gains when total daily protein is adequate (van Vliet et al. 2015; Morton et al. 2018). The daily total matters more than the source.
- Is soy protein as good as whey?
- For muscle-building it is close. Soy is a complete protein with a DIAAS near animal proteins, and it clears the leucine threshold at a reasonable dose, making it the strongest single plant protein. Whey still has a small per-gram edge on leucine content and digestion speed, but for practical muscle-building with an adequate daily protein intake, soy is a legitimate substitute, especially for people avoiding dairy.
- What about pea and rice protein?
- Individually, each is incomplete: pea is low in methionine, rice is low in lysine, and both are lower in leucine than whey. Blended together, they complement each other into a complete profile, which is why most quality vegan powders are pea-rice blends. Take a slightly larger serving than you would of whey to match the leucine threshold, and they build muscle effectively as part of an adequate daily protein intake.
- Which is cheaper, whey or plant protein?
- It depends on the metric. The fair comparison is not $/gram of protein but $/gram of leucine, since leucine drives the muscle-building effect and plant proteins carry less of it per gram. On that basis whey concentrate is usually the cheapest route to the threshold, with soy and quality blends competitive. Our protein powder ranking prices tested products by $/gram of leucine so you can compare whey and plant options on the metric that matters.
Every claim, cited.
- [01]Gorissen SHM, Crombag JJR, Senden JMG, et al. 2018. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids 50(12):1685-1695. Leucine and essential amino acid content of pea, rice, soy, and other plant isolates versus whey.
- [02]van Vliet S, Burd NA, van Loon LJC. 2015. The skeletal muscle anabolic response to plant- versus animal-based protein consumption. J Nutr 145(9):1981-1991. Animal protein edges plant per gram acutely; completeness and leucine explain the gap.
- [03]Morton RW, Murphy KT, McKellar SR, et al. 2018. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. Br J Sports Med 52(6):376-384. Daily target ~1.6 g/kg; total intake dominates source.
- [04]Moore DR, et al. Per-meal leucine threshold research. ~2.5-3 g leucine per meal for maximal muscle protein synthesis.
The Larderlab Team builds evidence-led frameworks for eating, lifting, and stocking a kitchen. We cite every claim. We publish the spreadsheet when possible. We buy what we review at retail price. When new data lands, we revise with a dated note.
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