What Is Pea Protein? Quality, Allergy and How It Compares

Pea protein is an ingredient extracted from yellow split peas, about 80% protein in the isolate, relatively high in lysine and low in methionine, which is why powders pair it with rice.¹ In the one human ileal study, co-authored by its maker, the isolate scored a DIAAS of 1.00 against 1.45 for milk casein, and two trials against whey found no significant difference.² Pea is not one of the UK's 14 labelled allergens, yet pea protein isolates have caused allergic reactions, including anaphylaxis, in people with legume allergy.^{3, 4} Part of the Wellgard vegan protein guide.

What is pea protein, and how is it made?

For an isolate, dried yellow split peas are milled, mixed with water, and the protein is separated from the starch and fibre, then dried: about 80% protein by weight, and in a 2018 analysis of commercial isolates pea protein ran from 77 to 81% between suppliers.¹ A concentrate is dry-milled and air-classified, keeps more starch and fibre, and carries a lower protein figure. The ingredients list says which you have; a bare "pea protein" is usually the isolate.

How much protein is in pea protein, and in peas?

A 25 g serving of an isolate at 80% protein gives about 20 g of protein. Whole peas are a different food: in the UK composition dataset, boiled peas carry 6.7 g of protein per 100 g, boiled split peas 8.3 g and dried raw split peas 22.1 g.⁵ So peas do not have more protein than eggs: boiled eggs carry 14.1 g per 100 g against 6.7 g for boiled peas.⁵

What amino acids does pea protein have?

In the 2018 analysis, pea isolate carried 4.7 g of lysine and 0.3 g of methionine per 100 g of powder, so lysine is its strength and methionine, with cysteine, its weak point; rice protein is the mirror image, which is why the two are blended.¹ Leucine ran from 5.1% of protein in hemp to 13.5% in corn, with milk at 9.0%; pea sat at about 7%, so a 20 g serving carries roughly 1.4 g.¹ Pea protein contains no isoflavones: the oestrogen question belongs to soya, answered on is soy protein bad for you.

How well is pea protein digested? DIAAS and digestibility

DIAAS, the FAO's digestible indispensable amino acid score, measures how much of each essential amino acid is absorbed by the end of the small intestine against a reference pattern; it is a scientific score, not a UK legal standard. In the only human study of a pea isolate, 15 healthy adults ate labelled pea protein or casein: real ileal amino acid digestibility was 93.6% for pea and 96.8% for casein, not significantly different, and the DIAAS was 1.00 for pea and 1.45 for casein.² Whole cooked peas score lower: 71.6% true ileal digestibility of essential amino acids in Indian adults, against 74.6% for chickpea and 63.2% for mung bean.⁶ Compilations pooling mostly animal-model data put pea and rice proteins below a DIAAS of 75, and a pig study put pea and brown rice concentrates below 75 while whey isolate scored 100 or more.^{7, 8} The isolate and the whole food are different numbers. What "complete" means is on what is a complete protein.

Does pea protein build muscle? What the two trials found

In the first trial, 161 men took 25 g of pea protein, whey or placebo twice a day for 12 weeks of resistance training: biceps thickness rose from 24.9 mm to 27.3 mm across the groups, with only a trend towards a difference between them (P = 0.09); in a sensitivity analysis of the weakest participants the pea group's gain was significantly larger than placebo's while whey differed from neither; strength rose equally in all three groups.⁹ The trial was funded and co-authored by the pea protein's maker. In an eight-week pilot of 15 trained adults on 24 g of whey or pea around high-intensity functional training, strength rose in both groups with no difference between them on any measure.¹⁰ A 2025 pooled analysis of 30 randomised trials found soya and milk protein no different for muscle mass across 17 trials, a small deficit for plant protein overall (SMD −0.20) driven by non-soya sources and plant-based diets, no difference in strength across 14 trials, and no significant effect in adults aged 60 and over.¹¹ No trial ranks pea above or below whey.

Can you be allergic to pea protein?

Yes. The UK's list of 14 allergens that must be emphasised on a label names soybeans, lupin, peanuts and tree nuts among others; peas, chickpeas, lentils and beans are not on it.³ Yet a Canadian paediatric case series described anaphylaxis to pea protein hidden in processed foods, and a 2024 allergy review describes severe reactions especially to pea and lupin, often in meat-substitute products made with legumes.^{4, 13} In a Dutch study of legume-allergic patients, co-allergy to other legumes was uncommon in peanut- and soya-allergic patients (16.7% or less), while pea-, lupin-, lentil- and bean-allergic patients were often also allergic to peanut (64.7 to 77.8%) or soya (50 to 64.7%).¹² Anyone with a legume or nut allergy speaks to their allergy clinic before trying a new isolate. The NHS says to see a GP if you think you have a food allergy, and to call 999 if lips, mouth, throat or tongue suddenly swell or breathing becomes difficult.¹⁴

Does pea protein cause bloating, and what does it taste like?

Pea isolate tastes earthy and can feel gritty, which is why powders flavour and blend it. Bloating usually traces to what sits beside the protein: sugar alcohols, gums and added fibre. The oligosaccharides that make a plate of peas gassy are largely left behind with the starch and fibre when the protein is isolated, so an isolate carries far less of them; that is label logic, not a trial result; a sensitive gut tests a half serving first. More on is vegan protein powder healthy.

How does pea protein compare with soya, rice, fava and hemp?

Composition, the score on file and allergen status, with no ranking.^{1, 3, 7, 8, 15}

Digestibility footnote: the pea isolate figure is from a human ileal study; the compilation pools published ileal data, mostly from pigs; PDCAAS uses a rat assay and is capped at 1.0. The leucine percentages come from one batch per source in the 2018 analysis.¹

Frequently asked questions

Is pea protein a complete protein?

"Complete" describes composition, not a benefit. In the maker-co-authored human ileal study the isolate's DIAAS of 1.00 meant every essential amino acid, methionine included, met the reference pattern after digestion.² See what is a complete protein.

Is pea protein good for you?

It is a concentrated food: a 25 g serving of isolate is about 20 g of protein with little fat or sugar.¹ The authorised wording in Great Britain is that protein contributes to the maintenance of muscle mass, usable for any food in which at least 12% of the energy comes from protein; it describes the nutrient, not a powder or a plant.¹⁶

Does pea protein have oestrogen?

No. Peas contain no isoflavones, the soya compounds that resemble oestrogen in structure.

Can you be allergic to pea protein but not to peas?

Anaphylaxis to pea protein hidden in processed foods has been reported in children, and the 2024 review flags concentrated legume isolates in meat substitutes as the concern; eating peas without trouble does not settle an isolate, so anyone with a legume or nut allergy asks their allergy clinic first.^{4, 13, 14}

When should you take pea protein?

Within the day, not within a window: spread protein across meals. Timing around training is on is vegan protein powder healthy.

Sources

1. Gorissen SHM, et al. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids, 2018. PubMed 30167963.
2. Guillin FM, et al. Real ileal amino acid digestibility of pea protein compared to casein in healthy humans: a randomized trial. American Journal of Clinical Nutrition, 2022. Co-authored by the pea protein's maker. PubMed 34665230.
3. Food Standards Agency. Allergen labelling for food manufacturers, published 14 December 2017. gov.uk.
4. Lavine E, Ben-Shoshan M. Anaphylaxis to hidden pea protein: a Canadian pediatric case series. Journal of Allergy and Clinical Immunology: In Practice, 2019. PubMed 30794967.
5. Public Health England. Composition of foods integrated dataset (CoFID), 2021. gov.uk.
6. Kashyap S, et al. True ileal digestibility of legumes determined by dual-isotope tracer method in Indian adults. American Journal of Clinical Nutrition, 2019. PubMed 31374575.
7. Herreman L, et al. Comprehensive overview of the quality of plant- and animal-sourced proteins based on the digestible indispensable amino acid score. Food Science and Nutrition, 2020. PubMed 33133540.
8. Bailey HM, Fanelli NS, Stein HH. Effect of heat treatment on protein quality of rapeseed protein isolate compared with non-heated rapeseed isolate, soy and whey protein isolates, and rice and pea protein concentrates. Journal of the Science of Food and Agriculture, 2023. PubMed 37357639.
9. Babault N, et al. Pea proteins oral supplementation promotes muscle thickness gains during resistance training: a double-blind, randomized, placebo-controlled clinical trial vs. whey protein. Journal of the International Society of Sports Nutrition, 2015. PubMed 25628520.
10. Banaszek A, et al. The effects of whey vs. pea protein on physical adaptations following 8 weeks of high-intensity functional training: a pilot study. Sports, 2019. PubMed 30621129.
11. Reid-McCann RJ, et al. Effect of plant versus animal protein on muscle mass, strength, physical performance, and sarcopenia: a systematic review and meta-analysis of randomized controlled trials. Nutrition Reviews, 2025. PubMed 39813010.
12. Smits M, et al. Co-sensitization between legumes is frequently seen, but variable and not always clinically relevant. Frontiers in Allergy, 2023. PubMed 37007648.
13. Abu Risha M, et al. Legume allergens pea, chickpea, lentil, lupine and beyond. Current Allergy and Asthma Reports, 2024. PubMed 38990406.
14. NHS. Food allergy, page last reviewed 20 August 2026. nhs.uk/conditions/food-allergy.
15. House JD, Neufeld J, Leson G. Evaluating the quality of protein from hemp seed products through the use of the protein digestibility-corrected amino acid score method. Journal of Agricultural and Food Chemistry, 2010. PubMed 20977230.
16. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.

General information, not medical advice. Anyone with a legume, peanut or soya allergy asks their allergy clinic or GP before trying a pea protein isolate.