Plant protein vs collagen: what the research does and doesn't show

The evidence doesn't support plant protein and collagen as interchangeable for building muscle. Plant protein sits inside the same broad protein-source literature as animal protein, with a small edge for animal sources in some groups; collagen's own strength finding is smaller and lower-certainty, and collagen is missing an essential amino acid that keeps it out of the "complete protein" category entirely.

What the evidence doesn't support

It doesn't support collagen as a substitute for a complete protein source on muscle-building measures: the one meta-analysis below measuring collagen's effect on maximal strength found a small effect (SMD 0.19) at low certainty. It doesn't support treating "plant protein" as one uniform category either — soy protein has direct trial evidence matching animal protein, but the broader plant-vs-animal literature found a slight edge for animal protein in some age groups, and neither result is specific to any one plant protein blend. And it doesn't support a head-to-head comparison at all: no trial we found tested collagen against a plant protein source directly in the same study. What follows are two separate research literatures, read side by side, not one trial deciding a winner.

What the trials found

A 2021 systematic review and meta-analysis pooled 16 randomized trials comparing animal and plant protein sources on lean mass and strength in adults across age ranges. Pooled, there was no significant overall difference in absolute lean mass or strength by protein source — but in adults under 50 specifically, animal protein produced 0.41 kg more absolute lean mass than plant protein (95% CI 0.08–0.74 kg), and animal protein was favored for percent lean mass overall. The trial didn't identify any arm using a fava bean or fermented yeast protein blend specifically; this is evidence about plant protein sources in general, not any one product.

The clearest exception in that literature is soy: a 2018 meta-analysis of 9 randomized trials (266 adults performing resistance training for at least 6 weeks) found soy protein supplementation produced muscle and strength gains similar to whey or other animal proteins — the most direct plant-protein result matching animal protein head-to-head.

Collagen's research base is separate. A 2024 systematic review and meta-analysis of 19 randomized trials (768 healthy adults) tested daily collagen peptide supplementation combined with at least 8 weeks of physical training. It found statistically significant improvements in fat-free mass (moderate certainty), tendon morphology and muscle architecture (very low to low certainty), and maximal strength — a small effect (SMD 0.19), rated low certainty by the review's own authors. That's smaller and less certain than the strength and lean-mass differences reported in the plant-versus-animal protein literature above.

There's also a structural reason collagen and a typical plant protein blend aren't interchangeable on paper before any trial runs: per the current PDCAAS (Protein Digestibility-Corrected Amino Acid Score) method, collagen lacks the essential amino acid tryptophan and is categorized as an incomplete protein source, according to a 2019 analysis of collagen's amino acid balance. A soy, pea or fava bean isolate can supply a fuller essential amino acid profile depending on the specific blend and how it's formulated; whether any individual plant protein product on the market actually does depends on its own label, not the ingredient category as a whole.

Outcome	Plant protein (general)	Collagen peptides
Lean mass vs. animal protein	No overall difference (16 trials); animal protein +0.41 kg in adults under 50	Not directly compared in this literature
Maximal strength vs. animal protein	Soy matched animal protein (9 trials, 266 adults)	Small effect vs. baseline (SMD 0.19), low certainty
Amino acid completeness (PDCAAS)	Depends on the specific source/blend	Lacks tryptophan; categorized incomplete
Direct head-to-head trial	None found	None found

Questions people ask

Is plant protein or collagen better for building muscle?

Plant protein's trial base — particularly soy — has shown results comparable to animal protein for muscle and strength gains in resistance-trained adults. Collagen's own strength finding, from a separate 768-person meta-analysis, is real but smaller (SMD 0.19) and rated low certainty by the review's authors. Neither literature tested the two against each other directly.

Is collagen a complete protein like plant protein?

Not by the standard PDCAAS measure — collagen lacks the essential amino acid tryptophan and is categorized as an incomplete protein. Whether a given plant protein product is "complete" depends on its specific amino acid profile, which varies by source and blend and should be checked on that product's own label rather than assumed from the word "plant."

Can I take plant protein and collagen together?

The research reviewed here doesn't test that combination, and we're not aware of a safety concern specific to combining the two as separate protein sources in a diet. This isn't guidance on amounts or timing — talk to a doctor if you're combining supplements for a specific medical reason.

Is collagen good for muscle recovery the way protein is?

Collagen's trial base includes some recovery-adjacent measures — the 2024 meta-analysis above found low-certainty improvements in reactive strength recovery after exercise-induced muscle damage — but its core strength effect is smaller and less certain than the protein-source literature covering plant and animal protein broadly.

When to talk to a doctor

Neither plant protein nor collagen is a treatment for a diagnosed muscle-wasting, connective-tissue or metabolic condition, and nothing in the research above supports using either as a substitute for medical evaluation. If you have a diagnosed condition affecting muscle or connective tissue, or take prescription medication, talk to a doctor before adding either supplement.

Related reading: plant protein: what the research shows and plant protein vs whey: what actually differs.