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# Protein sources compared: whey, plant protein and collagen
- URL: https://verinourishwomen.com/nutrition/protein-sources/
- Published: 2026-08-24T00:00:00.000Z
- Updated: 2026-08-24T07:49:50.000Z
- Description: Whey, soy, pea or collagen? Compare protein quality, scoop size and amino acids, including what collagen contributes and what it cannot replace.
- Author: VeriNourish Editorial Team
- Tags: Nutrition

*Reviewed by [Emma Carter, Senior Health & Nutrition Editor](https://verinourishwomen.com/emma-carter/)*

The argument about animal against plant protein is mostly the wrong argument. What matters is whether a source carries enough of the amino acids your body cannot make, and how much of it you have to eat to get them. On that measure some plant proteins do better than whey, while collagen contributes protein without supplying a complete amino-acid profile.

Here is what separates the sources, what the trials in women actually found, and what to buy.

## How protein sources are scored

The digestible indispensable amino acid score, DIAAS, rates a protein on whether it delivers enough of every amino acid the body cannot make, after allowing for how much survives digestion. Above 100 is excellent, 75 to 99 is good quality, and below 75 earns no quality claim at all.

A comparative review scored the common sources this way ([Food Science & Nutrition, 2020](https://pmc.ncbi.nlm.nih.gov/articles/PMC7590266/?ref=verinourishwomen.com)):

| Source         | DIAAS | Category         |
| -------------- | ----- | ---------------- |
| Casein         | 117   | Excellent        |
| Egg            | 101   | Excellent        |
| Potato protein | 100   | Excellent        |
| Soy            | 91    | Good             |
| Whey           | 85    | Good             |
| Pea            | 70    | No quality claim |
| Hemp           | 54    | No quality claim |
| Wheat          | 48    | No quality claim |
| Rice           | 47    | No quality claim |
| Gelatin        | 2     | No quality claim |

Two things in that table are worth stopping on. Soy scores above whey, which is not what the supplement aisle implies. And gelatin, which is collagen, scores 2.

## Whey against plant protein, head to head

The best test of whether animal protein is genuinely superior is to match the sources on leucine, the amino acid that triggers muscle building, and see what happens.

That trial exists, and its participants were mostly women. Sixty-one untrained adults, 42 of them women, trained three times a week for 12 weeks while taking either 19 g of whey isolate or 26 g of soy isolate, both delivering 2 g of leucine ([Int J Environ Res Public Health, 2020](https://pmc.ncbi.nlm.nih.gov/articles/PMC7312446/?ref=verinourishwomen.com)).

Both groups gained: 1.54 kg of lean body mass (95% CI 0.94 to 2.15), with leg extensor and flexor strength up in both. **No differences between the groups.**

The practical answer sits in the doses rather than the results: 26 g against 19 g. Matching whey on leucine took about a third more soy. That is the real cost of choosing a plant powder, and it is a bigger scoop, not a worse outcome.

![Two scoops side by side: a level scoop of whey protein beside a bottle of milk, and a noticeably heaped scoop of soy protein beside soybeans.](https://storage.ghost.io/c/57/09/5709dd99-0d8d-4e4f-a27f-18d807e14fbf/content/images/2026/08/comparison-1.webp) 

Matched on leucine, it took 26 g of soy to equal 19 g of whey. That is a bigger scoop, not a worse result.

## Collagen is protein, but it is incomplete

Collagen is sold beside whey, priced like whey and measured in grams like whey. It contributes protein, but it does not supply the same amino-acid mix as whey or soy.

Collagen contains no tryptophan, one of the nine indispensable amino acids, and is low in cysteine and methionine. That is why it is classed as an incomplete protein, and why gelatin lands at 2 on the quality scale. A modelling paper estimated that collagen peptides could make up to 36% of protein intake in a typical US diet while the diet as a whole still met indispensable amino-acid requirements ([Nutrients, 2019](https://pmc.ncbi.nlm.nih.gov/articles/PMC6566836/?ref=verinourishwomen.com)). That figure is not a clinical target, and it does not show that collagen supports muscle as well as a complete protein.

None of this means collagen does nothing. If you take 15 g of collagen, it counts as 15 g of protein on a nutrition label, but it should not displace complete sources in your day. Collagen can be part of your total. Dairy, eggs, soy, meat, fish or well-chosen plant combinations still need to supply the indispensable amino acids it lacks. Our [collagen guide](https://verinourishwomen.com/supplements/collagen/) covers what the skin evidence does and does not support.

## Mixing plants solves most of the problem

A low score on its own does not condemn a plant protein, because the gaps differ between sources and cancel out when you combine them. Pea with wheat reaches 85, and potato blended with other plant proteins reaches 100 ([Food Science & Nutrition, 2020](https://pmc.ncbi.nlm.nih.gov/articles/PMC7590266/?ref=verinourishwomen.com)). That is why most plant powders blend two or three sources instead of selling pea alone.

You do not need to engineer this meal by meal. Eating a range of plant proteins across the day does the same work.

One honest caveat if you eat mostly plants. In a large cohort study, total and animal protein intake tracked with lean mass while plant protein intake did not ([Nutrients, 2018](https://pmc.ncbi.nlm.nih.gov/articles/PMC6212815/?ref=verinourishwomen.com)). It is observational, so it proves nothing about cause, but it is a reason to count your grams rather than assume the number takes care of itself.

## What to actually buy

- **If you want the smallest scoop for the money,** whey or casein. Both are good to excellent quality and cheap per gram of usable protein.
- **If you avoid dairy,** soy isolate is the plant protein that stands on its own at 91.
- **If you dislike soy,** buy a blend rather than single-source pea or rice, and expect to use a slightly larger scoop.
- **Buy collagen for a collagen-specific goal,** not as a substitute for whey, soy or food protein. Count its grams, but do not let it displace complete sources.
- **Do not treat 1.62 g/kg as a hard ceiling.** In a meta-analysis of 49 resistance-training trials, the average added benefit for fat-free mass levelled off around that intake, with wide uncertainty between people ([BJSM, 2018](https://pubmed.ncbi.nlm.nih.gov/28698222/?ref=verinourishwomen.com)). Source matters less than reaching an appropriate total for you.

Our [protein guide](https://verinourishwomen.com/nutrition/protein/) covers how many grams you actually need at your weight and how to spread them through the day, which is the part most women get wrong before the source ever becomes the question.

## When the source genuinely matters

For most women eating enough total protein from mixed food, the source is a detail. It starts to matter in three situations: when you are training and want the most from each gram, when you eat entirely plant-based and your total is borderline, and after menopause, when holding muscle takes more deliberate effort. Our guide to [menopause](https://verinourishwomen.com/conditions/menopause/) covers what changes and why protein and resistance work move up the list.

If you are eating well below your target and reaching for powder to fix it, food is the cheaper answer. Powder is a convenience, not a category of nutrition on its own.

## Frequently asked questions

### Is whey protein better than plant protein?

Not by as much as the marketing suggests. In a 12-week randomized trial in untrained adults, mostly women, soy and whey matched for leucine produced the same gains: about 1.54 kg of lean body mass in both groups with no difference between them. The catch is the matching. It took 26 g of soy isolate to deliver the same 2 g of leucine as 19 g of whey isolate.

### Does collagen count towards my daily protein?

Yes, collagen contributes grams of protein, but it is incomplete. It lacks tryptophan and is low in some other indispensable amino acids, so it should not replace complete protein sources when your goal is meeting amino-acid needs or supporting muscle. Count it in your total, then make sure the rest comes from varied, higher-quality sources.

### What is DIAAS and why does it matter?

The digestible indispensable amino acid score rates a protein on whether it delivers enough of every amino acid your body cannot make, after accounting for digestion. Above 100 is excellent, 75 to 99 is good, and below 75 earns no quality claim. It is the most useful single number when comparing two protein powders.

### Which plant protein is best?

Soy scores highest of the common plant proteins at 91, ahead of pea at 70, hemp at 54 and wheat at 48\. Soy is the one plant protein that stands up on its own; the others work better blended, since combinations like pea with wheat reach 85.

### Do I need to combine plant proteins at the same meal?

No. Eating a range of plant proteins across the day covers the amino acids you need. Blended powders do the same job in one scoop, which is why most plant protein products mix two or three sources rather than selling pea alone.

## References

1. [Comprehensive overview of the quality of plant- and animal-sourced proteins based on the digestible indispensable amino acid score](https://pmc.ncbi.nlm.nih.gov/articles/PMC7590266/?ref=verinourishwomen.com) · Herreman L et al, Food Science & Nutrition, 2020
2. [No significant differences in muscle growth and strength development when consuming soy and whey protein supplements matched for leucine following a 12 week resistance training program in men and women: a randomized trial](https://pmc.ncbi.nlm.nih.gov/articles/PMC7312446/?ref=verinourishwomen.com) · Lynch HM et al, Int J Environ Res Public Health, 2020
3. [Significant amounts of functional collagen peptides can be incorporated in the diet while maintaining indispensable amino acid balance](https://pmc.ncbi.nlm.nih.gov/articles/PMC6566836/?ref=verinourishwomen.com) · Paul C, Leser S, Oesser S, Nutrients, 2019
4. [A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults](https://pubmed.ncbi.nlm.nih.gov/28698222/?ref=verinourishwomen.com) · Morton RW et al, British Journal of Sports Medicine, 2018
5. [Dietary protein sources and muscle mass over the life course](https://pmc.ncbi.nlm.nih.gov/articles/PMC6212815/?ref=verinourishwomen.com) · Nutrients, 2018