Protein powders compared: how good are whey, soy, pea and rice?

The values at a glance

The most direct comparison study comes from Mathai et al. 2017. They fed eight protein sources to pigs, including six powders, and determined the DIAAS for each. Because all powders were measured in the same study, the values compare well.

Rice protein is missing from this study. Instead, there is a rat study by Rutherfurd et al. 2015 that rated several powders using the stricter reference pattern for young children:

Whey: top scores, but not every powder is the same

Whey is limited by histidine in all studies and still leads the direct comparisons. In reviews that average many datasets, whey comes out lower: 85 in Herreman et al., 0.90 in Hertzler et al. (young child pattern), just below soy. The range is striking: Herreman et al. 2020 found values of 78 to 88 (young child pattern) for different whey products and suspect that purity and processing play a big role. Stroebinger et al. 2024 cite a range of 73 to 110 from the literature and conclude that whey of varying quality is on the market.

Casein and milk protein

Milk protein concentrate was the best powder overall in Mathai et al. 2017 (141 for adults) and also came out on top in Rutherfurd et al. 2015 (118). The limiting amino acids are methionine and cysteine. For skim milk powder, Mathai et al. explain this by the fact that its main protein, casein, contains little cysteine. For pure casein, Herreman et al. 2020 give an average of 117, though based on only two datasets.

Soy: the strongest of the plant powders tested

Soy protein isolate scored 98 for adults in Mathai et al. 2017 and around 90 in Rutherfurd et al. 2015 (young child pattern). That puts it clearly below milk protein concentrate, but close to whey concentrate (97.3 in Rutherfurd et al.). The limiting amino acids are methionine and cysteine. One advantage of the isolate over soybean meal: in the study by Mathai et al. it contained only about a third of the trypsin inhibitors, substances that slow down protein digestion.

Pea: solid, but with a methionine gap

Pea protein is limited by methionine and cysteine in all studies. The values:

• Pea protein concentrate: 62 (young children) and 73 (adults) in Mathai et al. 2017
• Pea protein isolate: 60.8 and 71.3 in Stroebinger et al. 2024
• Pea protein concentrate: 82.2 (young children) in the rat study by Rutherfurd et al. 2015

The two pig studies agree well. The studies don't explain why the rats show higher values. Differences in animal model, measurement method and product are obvious possible reasons.

Rice, hemp, lupin: little data

Rice protein is strongly limited by lysine: 37.1 in Rutherfurd et al. 2015, 47 on average in Herreman et al. 2020. For hemp (54) and lupin (68), there are only the averages from Herreman et al., for hemp from a single dataset. We found no measured values for isolates of these plants as sold in stores.

Blends: pea + rice and pea + whey

Because pea has little methionine and rice little lysine, they complement each other. Herreman et al. 2020 calculate a maximum of 84 for pea with rice at a 41 % rice share (young child pattern). Hertzler et al. 2020 cite data showing that blends with 40 to 90 % pea reach the maximum of 1.0 in the older PDCAAS, calculated with the adult reference pattern.

Milk works even better as a partner. In the pig study by Stroebinger et al. 2024, a mix of 25 % pea and 75 % whey scored 104 (young child pattern), higher than either powder alone. More on this in the article Combining proteins.

In the calculator: 30 g pea protein gets a DIAAS of 71, 20 g pea + 10 g rice gets 95.

Leucine and building muscle

For building muscle, leucine matters a lot alongside DIAAS. Hertzler et al. 2020 give about 8 % leucine in soy protein compared with around 12 % in whey. They describe the concept, popular among athletes, of aiming for 20 to 40 g of protein and 2 to 4 g of leucine per meal.

Plant powders still do well in training studies when the amount is right. Hertzler et al. summarize several studies in which rice or pea protein over 6 to 12 weeks produced results similar to whey. They conclude that about 40 g of plant protein a day or more can achieve similar effects. Sharma et al. 2025 write that you typically need 20 to 40 % more plant protein.

How reliable are the values?

• All values come from animal studies with pigs or rats. In Mathai et al., the powders were fed raw.
• The reference pattern changes the numbers by about 5 to 25 points, more for high values than for low ones. Values for young children and adults can't be compared directly.
• The study by Mathai et al. was funded by the dairy industry, the one by Stroebinger et al. through a consortium coordinated by the Global Dairy Platform. In Rutherfurd et al., a dairy company supplied the milk proteins, and one co-author works there. The review by Hertzler et al. was written by employees of a nutrition products company.
• Products differ depending on how they are made. The measured values apply to the powders tested, not to every brand.

Frequently asked questions

Sources

1. Mathai, J. K., Liu, Y. & Stein, H. H. (2017): Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS). British Journal of Nutrition 117, 490–499. doi:10.1017/S0007114517000125
2. Rutherfurd, S. M., Fanning, A. C., Miller, B. J. & Moughan, P. J. (2015): Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats. Journal of Nutrition 145, 372–379. doi:10.3945/jn.114.195438
3. Stroebinger, N., Hodgkinson, S. M. & Moughan, P. J. (2024): Pig true ileal digestible amino acid contents of individual ingredients are additive in mixed meals and allow accurate predictions of digestible indispensable amino acid score values. Journal of Nutrition 154, 3323–3330. doi:10.1016/j.tjnut.2024.09.020
4. Herreman, L., Nommensen, P., Pennings, B. & Laus, M. C. (2020): Comprehensive overview of the quality of plant- and animal-sourced proteins based on the digestible indispensable amino acid score. Food Science & Nutrition 8, 5379–5391. doi:10.1002/fsn3.1809
5. Hertzler, S. R., Lieblein-Boff, J. C., Weiler, M. & Allgeier, C. (2020): Plant proteins: assessing their nutritional quality and effects on health and physical function. Nutrients 12, 3704. doi:10.3390/nu12123704
6. Sharma, K., Zhang, W. & Rawdkuen, S. (2025): Dietary plant-based protein supplements: sources, processing, nutritional value, and health benefits. Foods 14, 3259. doi:10.3390/foods14183259

You can find values for individual foods and where they come from under Data & sources. How proteinscore calculates is explained under Method.