Rice protein contains all nine essential amino acids but is low in lysine. Learn how it is made, how its quality compares, what training studies show, what to know about arsenic and how to use it.
Rice protein is the protein extracted from rice, usually brown rice, sold as a powder with about 80 to 90 % protein. It contains all nine essential amino acids but too little lysine to be complete on its own, so it is usually blended with pea or soy. Below: how it is made, its quality, training studies, arsenic and uses.
Is rice protein a complete protein?
No, rice protein is not a complete protein on its own, although it contains all nine essential amino acids. A complete protein supplies each essential amino acid in at least the amount the body needs per gram of protein. Rice protein falls short in lysine: it provides roughly 3 g of lysine per 100 g of protein [1], while the WHO reference pattern for adults calls for 4.5 g [2]. Lysine is therefore its limiting amino acid, the one that caps how much of the protein the body can use for building new tissue.
Protein quality scores reflect this gap. In a study comparing 14 protein sources, rice protein concentrate scored about 0.42 on the PDCAAS and 0.37 on the stricter DIAAS, both limited by lysine and calculated with the reference pattern for young children [3]. For comparison, soy and milk proteins reach close to 1.0. The score describes rice protein as a sole protein source; in a mixed diet or a blend, other foods supply the missing lysine.
What is the amino acid profile of rice protein?
The amino acid profile of rice protein is low in lysine but comparatively rich in the sulphur-containing amino acids methionine and cysteine. This pattern is the mirror image of pea protein, which is rich in lysine and low in methionine. Rice protein also contains a moderate amount of leucine, the amino acid that acts as the main signal for muscle protein synthesis: a 30 g serving of rice protein powder provides about 1.5 g [1].
| Amino acid | Rice protein | What it means |
|---|---|---|
| Lysine | Low (limiting) | Needs a lysine-rich partner such as pea, soy or legumes |
| Methionine + cysteine | Comparatively high | Covers the typical gap of pea protein |
| Leucine | About 1.5 g per 30 g serving | Below the roughly 2.5 g often cited per meal for a maximal muscle response |
| All nine essential amino acids | Present | None is missing; one is too low |
Research often cites around 2.5 g of leucine per meal or shake for a maximal muscle protein synthesis response. Rice protein alone stays below this value per serving, so larger portions, blends or added leucine are common ways to close the gap. The leucine guide explains the threshold in detail.
How is rice protein made?
Rice protein is made by separating the protein in rice from its starch, which makes up most of the grain. Brown rice, or broken rice from milling, is ground into flour and mixed with water. Enzymes such as amylase then break the starch down into soluble sugars. Because the protein does not dissolve under these conditions, it can be separated from the sugary liquid by filtration or centrifugation. The protein fraction is washed, sometimes treated again with enzymes, and dried into a fine powder.
Commercial rice protein powders usually contain about 80 to 90 % protein, depending on how thoroughly the starch is removed. The remaining part is mostly carbohydrate, some fat and minerals. Rice protein powder tastes mild and slightly grainy, and its texture is a little sandier than soy or pea protein, which is another reason it often appears in blends rather than on its own.
Is rice protein good for building muscle?
Rice protein supports muscle gains as well as whey protein in the training studies that have compared them directly. In an eight-week study, trained men who took 48 g of rice protein isolate after resistance training gained the same lean mass, strength and power as those taking 48 g of whey protein isolate [4]. A second eight-week study using smaller 24 g doses also found similar changes in body composition and performance between rice and whey groups [5].
Both studies were small, with 24 participants each, and both studied young men with training experience, so they do not cover every group. Their participants also ate plenty of protein overall, which matters: protein contributes to the growth and maintenance of muscle mass, and the total amount across the day counts more than the source of a single shake. The broader comparison is in whey vs. vegan protein.
Why are rice and pea protein often combined?
Rice and pea protein are combined because their amino acid profiles complement each other. Pea protein is rich in lysine but low in methionine; rice protein is the opposite. Together, in ratios such as 70:30 or 50:50, they form a protein whose essential amino acids all meet requirements. This is the same principle as eating rice with lentils or beans, a combination found in cuisines around the world.
"Rice protein is not the strongest plant protein on its own, but it is a very useful partner. It brings the methionine that pea lacks, and pea brings the lysine that rice lacks." – Anna Falk, founder of WAM
Many powders add a third source such as soy, or extra leucine, to raise the leucine content per serving. A side-by-side comparison of rice, pea, soy and hemp protein, including texture and allergens, is in our guide Which Vegan Protein Is Best?.
Does rice protein contain arsenic?
Rice protein can contain traces of arsenic, because rice takes up more arsenic from soil and water than most other crops. The European Food Safety Authority names rice and rice-based products among the main sources of inorganic arsenic in European diets [6]. The EU sets maximum levels of inorganic arsenic for rice and several rice products, but not for protein supplements [7].
The amount in a finished powder depends on where the rice was grown, how it was processed and how the supplier controls quality. Manufacturers check raw materials with batch certificates, and independent laboratory tests of finished products add a second check. Our article on heavy metals in plant protein explains how to read such results and why trace amounts are found in most foods.
Who can use rice protein?
Rice protein suits most people, including those who avoid milk, soy or gluten. Rice is not one of the 14 major allergens that must be highlighted on food labels in the EU [8], and rice allergy is uncommon in Europe. Rice naturally contains no gluten, but powders can be produced in facilities that also handle wheat, so people with coeliac disease should check the label for a gluten-free statement.
Because rice protein is plant-based and free from milk ingredients, it also suits vegan diets and people with lactose intolerance. Anyone who relies on rice protein as their main protein source should combine it with lysine-rich foods such as legumes, tofu or pea protein across the day.
How do you use rice protein powder?
Rice protein powder works best in smoothies, porridge and baking, where its slightly grainy texture is less noticeable than in a plain shake. Mix 25 to 30 g into 250 to 300 ml of plant drink and blend with fruit or nut butter for a smoother result. For porridge, stir the powder into a little cold liquid first, then into the cooked oats. In baking, replace up to about a quarter of the flour with protein powder and add a little extra liquid. Recipes are on the WAM recipe blog.
FAQ: common questions about rice protein
Is rice protein a complete protein?
Rice protein contains all nine essential amino acids, but its lysine content is too low to meet requirements, so on its own it is not considered a complete protein. Combined with a lysine-rich protein such as pea, soy or legumes, it becomes part of a complete amino acid profile. This is why most rice protein powders are sold as blends.
Is rice protein good for building muscle?
Two eight-week studies in trained men found that rice protein, taken with resistance training, led to the same gains in lean mass and strength as whey protein, at doses of 48 g and 24 g. Rice protein contains less leucine per serving than whey, about 1.5 g per 30 g, but total daily protein intake and training matter more than the source of one shake.
How much protein does rice protein powder contain?
Rice protein powders usually contain about 80 to 90 % protein, so a 30 g serving provides roughly 24 to 27 g of protein when unflavoured. Flavoured products contain less per serving, because sweeteners, flavours and cocoa take up part of the weight. The rest of the powder is mainly residual carbohydrate from the rice starch, plus small amounts of fat and minerals.
Does rice protein contain arsenic?
Rice protein can contain trace amounts of arsenic, because rice absorbs more arsenic from soil and water than most crops. The level depends on growing region, processing and quality control. Reputable brands test raw materials and, ideally, finished batches in independent laboratories, and publish the results so you can check them yourself.
Is rice protein better than pea protein?
Neither rice nor pea protein is better on its own; they have opposite strengths. Pea protein is rich in lysine and leucine but low in methionine, while rice protein is low in lysine but higher in methionine. Combined, they cover each other's gaps, which is why blends of the two are common.
Is brown rice protein the same as rice protein?
Brown rice protein is rice protein made from whole-grain brown rice, which most commercial rice protein powders use. Because the starch, fibre and most other components are removed during processing, the final protein powder from brown or white rice is very similar. The term "brown rice protein" describes the starting material rather than a different type of protein.
Is rice protein suitable for people with allergies?
Rice is not one of the 14 major food allergens in the EU, and rice allergy is uncommon, so rice protein suits many people who avoid milk, soy or gluten. Rice contains no gluten naturally, but powders can be cross-contaminated during production. People with coeliac disease or several allergies should check the label and the manufacturer's allergen statement.
WAM Protein: rice protein in a three-source blend
WAM Protein combines rice protein isolate with soy and pea protein and added leucine, so each 30 g serving provides 21–23 g of protein, depending on the flavour, and 2.5 g of leucine in total. Selected batches of every flavour are tested by Eurofins, an independent accredited laboratory, and lead, cadmium, mercury and arsenic were below the lab's limit of quantification in all reports so far; the results are on our Heavy Metals & Testing page. WAM contains soy, so it is not suitable for people with a soy allergy.
Sources
[1] 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):1685-95. PubMed
[2] WHO/FAO/UNU Expert Consultation. Protein and amino acid requirements in human nutrition. WHO Technical Report Series 935. Geneva: WHO; 2007. WHO
[3] Rutherfurd SM, Fanning AC, Miller BJ, Moughan PJ. Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats. J Nutr. 2015;145(2):372-9. PubMed
[4] Joy JM, Lowery RP, Wilson JM, et al. The effects of 8 weeks of whey or rice protein supplementation on body composition and exercise performance. Nutr J. 2013;12:86. PubMed
[5] Moon JM, Ratliff KM, Blumkaitis JC, et al. Effects of daily 24-gram doses of rice or whey protein on resistance training adaptations in trained males. J Int Soc Sports Nutr. 2020;17(1):60. PubMed
[6] EFSA Panel on Contaminants in the Food Chain (CONTAM). Update of the risk assessment of inorganic arsenic in food. EFSA Journal. 2024;22(1):e8488. EFSA
[7] Commission Regulation (EU) 2023/915 on maximum levels for certain contaminants in food. EUR-Lex
[8] Regulation (EU) No 1169/2011 on the provision of food information to consumers, Annex II. EUR-Lex
