How do whey, casein and plant proteins differ?

Protein ingredients made from plants come mainly from soybeans, peas and rice, while whey and casein are both proteins from milk. They differ in where they come from, how much of the powder is protein, and the proportions of amino acids in the protein. As for the daily amount, the Thai Reference Daily Intake (Thai RDI) for protein is 50 g a day, and that counts protein from every food you eat that day, whether plant or animal.

In short:

• Plant protein ingredients: mainly soy, pea and rice; wheat, potato, oat and corn are also used
• Milk protein ingredients: whey (from the liquid left in cheesemaking) and casein (another milk protein)
• How they differ: source, protein share of the powder, and amino acid proportions
• Essential amino acids: the share in the protein differs by source (2018 analysis; tryptophan not measured)
• Daily protein: Thai RDI 50 g, from all foods together

This article explains the types of protein ingredient by their source and composition.

What plant proteins are there, and how much protein do you need a day?

When people talk about "plant protein" as an ingredient, they usually mean protein that has been separated from a plant and dried into a powder. The most common sources are soybeans, peas and rice.

Which plants are protein ingredients made from?

A 2018 study by Gorissen and colleagues at Maastricht University in the Netherlands analysed 35 commercially available protein powders using the same laboratory method for all of them. The plant sources were oat, lupin, wheat, hemp, microalgae, soy, brown rice, pea, corn and potato. The animal sources were milk, whey, caseinate, casein and egg.

The researchers also noted how much each plant contributes to the plant protein people eat worldwide, based on United Nations food supply data: wheat about 32.3%, rice about 20.6%, corn about 7.3%, potato about 3.1%, soy about 2.7% and pea about 1.0%. Among the sources listed, rice, the staple of Thai meals, is second only to wheat.

How much protein do you need a day?

The Thai RDI for protein is 50 g a day. It applies to the general population aged 3 and over and is based on an intake of 2,000 kcal a day. It is a total for the whole day, from rice, eggs, fish, meat, milk, tofu and beans alike, not an amount to get from one kind of protein ingredient.

Has protein from Thai rice varieties been studied?

Thai researchers have studied protein from local rice varieties. A 2025 study by Onsaard and colleagues at Ubon Ratchathani University extracted protein from young and mature grains of four Thai varieties: Jasmine Rice 105 (Khao Dawk Mali 105), Hom Warin, RD6 and Hom Naka. Protein extracts from young grains of Hom Naka and Hom Warin had 633.3 g of protein per kg, more than those from mature grains. The study looked at extracts made in the laboratory, not at rice as it is cooked and eaten.

What is whey, and how are concentrate, isolate and hydrolysate different?

Whey is a by-product of cheesemaking. US federal regulations define it as the liquid left after the curd is separated from milk, cream or skim milk in cheesemaking.

How much of milk becomes whey?

Most of it, by volume. A 2024 review by Irazoqui and colleagues from Argentina's dairy research institute (CONICET-INTA) says whey makes up about 85–95% of the milk's volume and keeps much of its nutrients, mainly protein and lactose. In liquid form, though, whey is dilute: the US Department of Agriculture's FoodData Central lists 0.85 g of protein per 100 g of liquid sweet whey, and 12.9 g per 100 g of dried sweet whey.

Whey ingredients compared

The US rule for whey protein concentrate says it is made by physical separation, such as precipitation, filtration or dialysis, and sets a fat content of 1–10%. Because the rule only sets a minimum of 25% protein, a product called "whey protein concentrate" can vary widely. In the 2018 Maastricht analysis, the three whey samples measured 72–84% protein.

What is a hydrolysate like?

In a hydrolysate, the protein has been cut into smaller pieces. The 2024 review by Irazoqui and colleagues says products from whey can be made by physicochemical, microbial or enzymatic treatments. A 2010 study by Leksrisompong and colleagues at North Carolina State University examined 22 whey protein hydrolysates from 8 major manufacturers. Samples with a higher degree of hydrolysis (more of the protein broken down) had more small peptides and tasted more bitter. Potato-like or brothy, malty and animal-like flavours were also typical.

How is casein different from whey?

Both are proteins from milk. Whey is defined by where it comes from, the liquid left after the curd is removed in cheesemaking, while casein and caseinate, such as calcium caseinate, were analysed as separate milk proteins in the 2018 Maastricht study.

Casein and whey compared

Source: protein and amino acid figures from Gorissen and colleagues (2018), three whey and two casein samples. In the same analysis, milk protein (which contains both) had 39% essential amino acids and calcium caseinate 38%.

How do the amino acids in each protein differ?

Every protein is made of amino acids, and nine of them, the essential amino acids, must come from food. For the full list, see What are essential amino acids? The 2018 analysis measured how much of each protein is made up of essential amino acids.

Essential amino acids and protein content (2018 analysis)

Source: Gorissen and colleagues 2018. Tryptophan was not measured, so the totals cover the other eight essential amino acids. The researchers found that the average for plant proteins (26% of protein) was lower than for animal proteins (37%), and that the total for soy, brown rice, pea, corn and potato protein met the reference requirement for essential amino acids of the WHO/FAO/UNU expert consultation that the study used. The figures are totals; they do not show each amino acid separately.

What are the limits of these figures?

The 2018 analysis tested only one to seven samples per source; brown rice and egg were one sample each. Protein content varied between suppliers, for example from 61% to 91% for soy. The figures describe the powders that were tested, not every product on the market.

How much protein do Thai people get?

Two studies of adults in Bangkok give a picture of how much protein people eat and where it comes from.

Matsuda-Inoguchi and colleagues concluded that protein intake was sufficient in most of the women they studied. In the Mahidol University study by Ivanovitch and colleagues, median energy intake was 1,485 kcal a day in men and 1,428 kcal in women. Both studies were small, covered only Bangkok, and relied on a few days of records, so they show a pattern rather than national figures.

What does protein do in the body?

Protein contributes to growth and helps repair body tissue; is a source of essential amino acids for body protein synthesis; and contributes to the maintenance of normal bones. These roles belong to protein as a nutrient, whatever its source.

Who should be careful with whey, casein or soy protein?

People who react to milk or soy

Milk and soybeans are among the nine major food allergens listed by the US Food and Drug Administration, along with eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat and sesame. Whey and casein come from milk, and soy protein from soybeans. The FDA advises always reading food labels and avoiding foods you are allergic to.

Lactose in whey ingredients

Lactose is the natural sugar in milk. Under US regulations, dried whey can be 61–75% lactose, and whey protein concentrate can contain up to 60%.

If a doctor has told you to limit protein

If a doctor has told you to limit how much protein you eat, follow that advice.

If you are pregnant, breastfeeding, take regular medication or are under a doctor's care, speak to a doctor or pharmacist before taking dietary supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.