Whey Protein or Pea Protein: What's the Difference

Whey and pea protein often sit on the same shelf, but they come from different worlds: the first is a by-product of cheesemaking, the second a concentrate of legume protein. Our editorial team examined how they differ in composition, absorption and scientific data, so that the comparison rests on facts rather than marketing.

Where each protein comes from

Whey protein is obtained from milk whey - the liquid that remains after milk curdles during cheese production. Whey contains about a fifth of all the proteins in milk; the rest is casein. Through membrane filtration, water, lactose and fat are removed from it, yielding a concentrate, isolate or hydrolysate.

Pea protein is produced from yellow split peas. The legumes are ground into flour, the protein fraction is separated from the starch and fibre by means of aqueous extraction and precipitation, and then dried. Quality pea protein isolates contain more than 80% protein on a dry-matter basis.

The technological difference matters to the consumer: whey is by definition a dairy product, so it may contain traces of lactose and milk allergens. Pea protein is plant-based from the outset, contains no lactose and is not among the main food allergens listed in the EU regulation on food labelling.

Another difference is the "natural" purpose of the protein. Whey proteins are evolutionarily meant for the rapid nourishment of a newborn mammal, so they dissolve easily and are digested quickly. The storage proteins of peas, vicilin and legumin, have a different structure that is partly protected from enzymes until technological processing breaks it down.

• Whey:animal origin, dairy allergen, high solubility.
• Pea:plant origin, lactose-free, thicker texture.
• In common:both are produced as concentrates and isolates of varying degrees of purity.

Amino acid profile and leucine

For muscle growth, what matters is not only the amount of protein but also the content of essential amino acids, especially leucine. Leucine acts as a signal that triggers muscle protein synthesis via the mTOR pathway. It is precisely on this measure that whey traditionally leads among popular proteins.

An analysis of commercial plant isolates carried out by Gorissen and colleagues (2018) showed that pea protein has noticeably less leucine and total essential amino acids than whey. At the same time, among plant sources pea looks like one of the best options and outperforms, for example, wheat protein.

Pea's weak point is the sulphur-containing amino acid methionine. On the other hand, it is rich in lysine and arginine. That is why manufacturers often blend pea protein with rice: rice is low in lysine but richer in methionine, and the mixture gives a more balanced profile.

In practice, the lower leucine concentration can be partly compensated for by a larger serving. Researchers agree that plant protein in a somewhat larger dose can bring the anabolic response close to that of animal protein (van Vliet et al., 2015).

Absorption and protein quality

Protein quality is assessed on the PDCAAS scale and the newer DIAAS, which was recommended by an FAO expert consultation in 2013. DIAAS takes into account the digestibility of each amino acid separately in the small intestine, so it more accurately reflects the real value of a protein.

Whey protein receives the highest scores on both scales. Pea protein is usually rated slightly below one on PDCAAS, and on DIAAS it falls short of milk proteins because of a deficit of sulphur-containing amino acids (Mathai et al., 2017).

The rate of absorption also differs. Whey is soluble in the acidic environment of the stomach and passes quickly into the intestine, so the level of amino acids in the blood rises within half an hour. Pea protein is digested somewhat more slowly; its amino acid "wave" is lower but longer.

The digestibility of pea isolate is quite high, because during production the trypsin inhibitors and a significant part of the antinutrients characteristic of raw legumes are destroyed. Therefore it is incorrect to judge pea protein by the properties of raw peas.

For most people the difference in absorption rate is not decisive, as long as total daily protein intake is sufficient. The ISSN position (Jäger et al., 2017) emphasises that it is precisely the daily amount of protein that is the main factor in the result.

What research says about muscle

The best-known direct comparison is the randomised study by Babault and colleagues (2015). Young men trained for 12 weeks and received 25 g of protein twice a day: pea, whey or placebo. The increase in biceps thickness in the pea group did not differ statistically from the whey group.

It is important to understand the limitations: the sample was small, and the participants were relatively untrained. In such people, muscles grow quickly even with less-than-ideal nutrition, so it is hard to detect a subtle difference between proteins.

A study on vegans and omnivores (Hevia-Larraín et al., 2021) showed that with a sufficient daily amount of protein (about 1.6 g/kg) a plant-based diet with protein supplements provided the same increase in muscle mass as a mixed one. This confirms: the daily amount matters more than the source.

At the same time, acute studies of muscle protein synthesis within a few hours usually record an advantage for animal proteins at equal doses. The conclusion: in the short term whey is more effective per gram, in the long term the difference is levelled out by an adequate amount and regularity.

Taste, solubility and tolerance

Whey isolate dissolves almost instantly, has a neutral taste and is easily flavoured. Pea protein produces a thicker shake with a characteristic "beany" aftertaste, which manufacturers mask with cocoa, vanilla or by blending with other plant proteins.

From the standpoint of digestion, each option has its "problem" consumers. People with lactose intolerance may experience bloating from whey concentrate; the isolate contains far less lactose and is tolerated better. Pea protein contains no lactose, but in sensitive people it sometimes causes gas.

Allergy to cow's milk protein is a direct contraindication to whey. In such cases pea protein is considered an alternative, although cross-reaction with other legumes, in particular peanuts, is possible in isolated individuals.

A separate aspect is heavy metals. Plant proteins can accumulate them from the soil, so for pea protein it is especially important to choose manufacturers who publish laboratory certificates of analysis.

Editorial conclusions

Whey and pea protein differ in origin, amino acid composition and absorption rate. Whey has a higher biological value and more leucine per gram, while pea is plant-based, lactose-free and deficient in methionine.

Research shows that with a sufficient daily amount of protein and regular training the results in muscle mass can be comparable. A serving of pea protein for an equal effect may need to be slightly larger.

The choice depends on a person's diet, tolerance and values, not on which protein is "more correct".

If this topic interests you, we also recommend reading our articles on how to read a protein's amino acid profile, on protein requirements for strength training and on rice-pea blends for vegans.

References

1. Babault N, Païzis C, Deley G, et al. Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, placebo-controlled clinical trial vs. whey protein. J Int Soc Sports Nutr. 2015;12(1):3.
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.
3. 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.
4. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
5. Hevia-Larraín V, Gualano B, Longobardi I, et al. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: a comparison between habitual vegans and omnivores. Sports Med. 2021;51(6):1317–1330.
6. Mathai JK, Liu Y, Stein HH. 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). Br J Nutr. 2017;117(4):490–499.
7. FAO. Dietary protein quality evaluation in human nutrition: report of an FAO Expert Consultation. FAO Food and Nutrition Paper 92. Rome: FAO; 2013.