Is it true that you cannot get amino acids from plant-based protein?

Is it true that "you can't get amino acids from plant-based protein"?

Do you ever worry about whether you're getting enough amino acids while maintaining a diet centered on tofu, natto, and brown rice? In this article, we explain the relationship between essential amino acids and plant-based foods, as well as the reasons why people say you "can't get them" from plants.

There are 9 essential amino acids, and they are actually contained in plant-based foods as well

The protein that builds your body is made up of 20 types of amino acids. Among these, the ones that the body cannot produce in sufficient quantities and must be obtained through diet are called essential amino acids. Materials from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) also define essential amino acids as those that are not synthesized in the body, or are not synthesized sufficiently and must be obtained through diet, noting that there are 9 such types for humans.

A common misunderstanding here is the idea that "plant-based foods do not contain essential amino acids." In reality, all 9 essential amino acids are present in plant-based foods like tofu, natto, brown rice, and oatmeal. The difference lies in the varying amounts of each amino acid from one food to another. The method for comparing these differences in quantity numerically is the amino acid score, and you can check whether plant-based foods can maintain a high score in our article: What is an amino acid score? Can plant-based foods reach 100?

Why is it said that you "can't get them"?

One reason why it is said that "you can't get plant-based protein" is that people often compare amino acid levels based on a single specific food, such as eating only white rice or only white bread. While grains and legumes contain all 9 essential amino acids, some of them may be present in smaller amounts than in animal products; focusing solely on this difference can easily lead to the impression that they are "insufficient."

However, having a smaller amount of a certain amino acid is a different matter from not being able to get it at all. If you combine multiple plant-based foods in your daily meals—such as tofu, natto, rice, and vegetables—they can compensate for each other's deficiencies. When choosing foods, it is important not to look only at the amount of protein, but to consider the entire diet, including energy and other nutrients.

What exactly does an amino acid score represent?

The "amino acid score" number you see on food packaging and in nutrition discussions is an index representing how efficiently the protein contained in a food works for the body. Knowing what the number is being compared to can change your perspective.

Comparison with the "model" amino acids necessary for the body

An amino acid score is not determined by measuring a food's quality in a vacuum. The FAO (Food and Agriculture Organization of the United Nations) presents the amino acid score as a method calculated from the ratio between the amount of a target amino acid in the test protein and the same amino acid in a reference pattern (FAO report). This "reference pattern" is essentially the blueprint for the amino acids needed by the body. MEXT materials also describe the composition of essential amino acids that should be contained in dietary protein as an amino acid scoring pattern (MEXT Standard Tables of Food Composition in Japan, 2020 Edition (Eighth Revision) Amino Acid Composition Table). In short, the amino acid score is a numerical representation of how close the composition of a food is to the model composition. When choosing foods, it will change your perspective if you understand not just this number, but also what it is being compared to.

Foods with low scores still contain essential amino acids

It might sound like there are almost no essential amino acids in a food when its amino acid score is low. However, what the score represents is the fact that there is an amino acid with a lower quantity compared to the model composition, not that essential amino acids are absent. The FAO also presents the Digestible Indispensable Amino Acid Score (DIAAS) as an index for evaluation by comparing the amount of digestible indispensable amino acids in dietary protein with the same amino acids in a reference protein. Even when considering digestibility, the axis of evaluation is the "balance of quantities." For foods with low scores, it is better to think of combinations where you can compensate for the amino acids that are low in quantity with other foods. Which amino acids are low is determined by the food itself.

Foods and patterns where plant-based protein is prone to amino acid deficiency

While essential amino acids are present in plant-based foods, the types that tend to be low vary depending on the food. The types of amino acids that are prone to deficiency differ between grains, which are often the staple food, and soy or other legumes.

The essential amino acid called lysine, which is low in rice and wheat

Perhaps there are days when you make do with just toast for breakfast or just pasta for lunch. Explanations by the Ministry of Health, Labour and Welfare refer to essential amino acids that fall short of the amounts needed by the body as limiting amino acids, and lysine is cited as one such amino acid in the protein of rice, wheat, and corn. Lysine is one of the 9 essential amino acids that the body cannot create on its own and must obtain through food. If you have days where you eat only grains like rice, white bread, or noodles, it is a combination prone to lysine deficiency. Meals where you eat rice with only pickles or furikake are also an example where the proportion of grains is likely to be high. For those whose staple food is grains, being conscious of eating foods high in lysine—such as meat, fish, eggs, or soy products—can help prevent an imbalance in essential amino acids.

Sulfur-containing amino acids that are low in soy and legumes

There may also be people whose main dish consists of tofu or natto. MEXT materials treat methionine and cystine (cysteine) as sulfur-containing amino acids. The protein in soy and legumes is a food source where these sulfur-containing amino acids are lower compared to grains. As mentioned above, while grains are prone to being low in lysine, soy and legumes are prone to being low in different types of amino acids. Trying to cover your protein intake for a meal with only soy products like tofu, natto, or soy milk is likely to result in a menu low in sulfur-containing amino acids. Eating grains like rice or brown rice together, or adding a small amount of egg or fish, will make it easier to supplement sulfur-containing amino acids.

How to supplement amino acids that are prone to deficiency

As mentioned above, rice and wheat are low in lysine, while soy and legumes are low in sulfur-containing amino acids. Here, we address how to combine these two types of foods, and whether it is necessary to have them all at every meal.

The concept of combining grains and legumes

There are ways like putting natto on your rice for breakfast, or adding a glass of soy milk to your toast. These combinations supplement the lysine that is low in rice and wheat with foods derived from soybeans.

A review of plant-based protein suggests a combination ratio of about 2:1 for grains and legumes to complement each other's amino acid profiles (Article published on PubMed Central). Think of it as adding a slightly generous portion of tofu, natto, or soy milk to your rice.

You do not need to have the exact same combination every day. By being mindful of menus that include both grains and legumes together—such as having tofu miso soup or natto with rice, or pairing edamame or soy milk with bread—you can supplement both lysine and sulfur-containing amino acids without effort. It is also worth remembering that choosing brown rice or whole wheat bread makes it easier to balance amino acids than using refined grains.

Is it necessary to have them all at the same meal?

There may be days when your grains and legumes are split across different meals, such as having only bread for breakfast, a tofu dish for lunch, and natto rice for dinner. In this case, you might be concerned that they aren't balanced within a single meal.

The Position Paper of the Academy of Nutrition and Dietetics (Academy of Nutrition and Dietetics Position Paper on Vegetarian Diets) and a paper in the Medical Journal of Australia state that as long as you consume sufficient energy and eat a variety of plant-based foods daily, you do not need to strictly combine grains and legumes at every single meal. In other words, even if your meals are separated, such as bread for breakfast and a tofu dish for lunch, if you eat both grains and legumes within the day, it is considered a valid way to supplement amino acids.

You don't need to feel pressured to have grains and legumes at every meal; if you are conscious of eating a balanced diet throughout the day, it will be easier to maintain. Even if you have days during the work week when you are busy and reduce the number of items on your plate, we recommend being mindful of a menu that incorporates both grains and legumes over the course of the week.

Can you meet your daily requirements with only plant-based foods?

It is worth wondering if you can meet the required daily protein intake with a diet centered on tofu, natto, and brown rice. We will introduce specific ways to estimate the amount based on body weight and combinations that are easy to try for breakfast, lunch, and dinner.

Estimated daily protein requirements

Let's consider a person weighing 60kg as an example. The Dietary Reference Intakes for Japanese (2010 edition) from the Ministry of Health, Labour and Welfare sets the estimated average protein requirement for adults at 0.65g per kg of body weight. Applying this to a 60kg body weight, the guideline is approximately 39g per day.

The estimated average requirement mentioned here is a value indicated as a level at which half of the population can meet their needs. Because the amount needed varies depending on physique and activity level, it is best to accept the 39g figure as a starting point.

Trying to meet this amount solely with plant-based foods naturally increases the number of items you eat. You would likely combine soy products like tofu and natto with grains like rice and bread, and add small amounts of protein from vegetables and tubers. It is more realistic to combine several items rather than trying to complete it with just one dish.

Examples of combinations to try for breakfast, lunch, and dinner

For breakfast, putting natto on rice and adding a tofu miso soup allows you to take in a combination of grains and soy products at once. If you eat deep-fried tofu (atsuage) or soy-based "mince" with rice for lunch, you can continue with the same concept. For dinner, just combining the plant-based foods you have on hand, such as a soup using edamame or soy milk, is sufficient.

Even if you don't have both grains and legumes at every meal, if you split them up across several meals during the day, it becomes easier to supplement the amino acids that are prone to deficiency, as mentioned above. On days when you find it difficult to plan your menu, incorporating plant-based protein powder is also one way. Points to keep in mind when choosing are summarized in What are the disadvantages of plant-based protein? An explanation of how to view protein, carbohydrates, taste, and ingredients, so please refer to that as well.

Is plant-based protein inferior to animal-based?

Research has shown that there are differences in how plant-based and animal-based proteins are absorbed by the body. However, this difference does not immediately imply superiority or inferiority in terms of the body's needs. Let's look at what is known and to what extent.

Differences in absorption speed and impact on the body

The way blood amino acid concentrations rise after consumption differs depending on the type of protein. In a 2013 paper published in the International Journal of Food Sciences and Nutrition, a randomized, double-blind, crossover trial was conducted with 8 healthy individuals consuming 20g of protein (Paper published on PubMed (2013)). The results showed that potato protein caused blood amino acid levels to rise moderately and gradually, whey protein caused a sharp and large rise, and casein showed a trajectory similar to the high molecular weight fraction but with higher concentrations.

Also, in a 2019 paper in the Journal of Molecular Nutrition & Food Research, a randomized crossover trial involving 21 healthy individuals performing a meal challenge was conducted (Paper published on PubMed (2019)). The results showed that after consuming a vegan breakfast, the postprandial response of 9 amino acids was actually higher compared to after consuming an animal-based breakfast. However, this study did not investigate whether the essential amounts of amino acids themselves were sufficient. You cannot definitively say that plant-based protein works against the body just because the speed of absorption and changes in blood concentration are different.

Are there differences in impact on muscle mass or strength based on the origin?

A study that compares the protein source itself is helpful for considering the impact on the body. A 2021 paper analyzed 16 out of 18 randomized controlled trials targeting adults in a meta-analysis (Paper published on PubMed (2021)). The results showed that there was no difference in absolute fat-free mass or muscle strength changes depending on whether the protein was plant-based or animal-based.

If you only look at the single difference of absorption speed, you might feel that plant-based protein is inferior. However, in this meta-analysis that actually investigated physical changes, no difference was found based on the source. You don't need to think that you are at a disadvantage just because you continue to eat a diet centered on tofu and natto. As mentioned above, there are amino acids that are prone to being low in certain foods, so what you should worry about is not the superiority of the source, but how you combine them.

Is it okay to consume too much plant-based protein?

When you have days where you consciously eat more tofu, natto, and legumes, you might worry about whether you are consuming too much protein. Here, we touch upon the daily guideline figures and what to watch out for when increasing intake.

Is 100g per day considered too much?

If you eat tofu, natto, and soy milk all at once, there may be days when the total protein exceeds 100g (Ministry of Health, Labour and Welfare "Points for Formulating Dietary Reference Intakes for Japanese (2025 edition)"). The target protein range is set at 20% of energy for those aged 1 and over. Since protein is 4kcal per 1g, for someone consuming 2000kcal per day, the upper limit is 400kcal's worth, or 100g. A protein intake of 100g per day is exactly at the upper limit for someone consuming 2000kcal, and this alone does not determine it as "too much." However, it is useful to remember as a guideline for days when your food intake is high or when you have a combination of tofu, natto, and soy milk, so that you can keep an eye on the numbers.

Things to watch out for as signs of over-consumption

When you try to increase protein with plant-based foods, you tend to eat more legumes and grains than usual. These foods contain not only protein but also carbohydrates and energy. Therefore, when you increase the amount you eat with the intention of increasing protein, carbohydrates and energy increase along with it. Before you increase your intake by looking only at the protein numbers, reflect on whether you have been eating the same foods for many days, and whether the total amount of your daily meals has increased significantly compared to your usual intake. Checking the heat quantity (calories) along with the protein amount in the nutritional labeling will serve as a guide for whether you are increasing your intake too much. If you find yourself frequently eating specific legumes or soy products in large quantities over consecutive days, we recommend reviewing the amount.

How to choose foods to easily supplement plant-based protein?

There may be days when it's difficult to prepare tofu or natto for every meal. When relying on general foods, usability changes depending on where you look on the raw material labeling and what shape you choose.

What can be read from the raw material labeling

When choosing plant-based protein foods, the first thing to look at is the raw material labeling. The Consumer Affairs Agency explains that raw materials are displayed by their common names, in descending order of usage weight (Consumer Affairs Agency "Food labeling you should know"). In other words, if you are choosing with the expectation of protein derived from soy or legumes, checking whether those appear near the top of the raw materials will give you an idea of how much is actually used. Additionally, processed foods in containers and packaging require labeling of heat quantity (calories), protein, fat, carbohydrates, and salt equivalent (Consumer Affairs Agency "Food Labeling Guide"). By looking not only at the amount of protein but also at the order of the raw materials, you can grasp what the food is deriving its protein from.

The option of portable foods

It is not realistic to prepare refrigerated foods like tofu or natto while on the go or at work. Plant-based protein foods that can be stored at room temperature and are individually wrapped are easy to keep in a bag or a desk drawer, and are suitable for carrying on days when your meal intervals are likely to be long. Consumer Affairs Agency materials list meat, seafood, soy/soy products, eggs, and dairy as the main sources of protein, and suggest combining these with grain-based staples (Consumer Affairs Agency "Eat protein, fat, and carbohydrates in a balanced manner"). When choosing something to carry, checking the raw material labeling to see if it uses soy-derived protein will help you choose something suitable for the purpose of supplementing plant-based protein. For those who want to avoid animal-based raw materials, we recommend checking the raw material labeling as well.

BRAIN PRO's raw materials and amino acid supplementation

So far, we have looked at the concept of meeting amino acid needs with only plant-based foods. Finally, we will specifically check the raw materials and nutritional components of BRAIN PRO as a general food that does not use animal-based raw materials.

Characteristics of raw materials, including pea protein

The raw materials for BRAIN PRO are almond paste, pea protein, almonds, soy puffs, cocoa powder, coconut oil, cacao butter, inulin syrup, agave syrup, yamabushitake (lion's mane) mushroom powder, rock salt, flavoring, and sweetener (stevia). Pea protein is a plant-based protein made from peas, and with the addition of soy puffs and almonds, the protein source is composed entirely of plant-based materials. No white sugar, preservatives, wheat, casein, trans fatty acids, animal-based materials, or coloring agents are used. For those who structure their menus around tofu, natto, and soy milk, it can be said that this is an easy-to-choose option if you want to avoid animal-based products starting from the ingredient level. Since it contains soy and almonds as raw materials, those with allergies to these should be careful. Stevia is used as a sweetener, and white sugar is not used. Because raw materials are listed in descending order of weight used, the almond paste and pea protein at the beginning are the main components of BRAIN PRO.

Comparing the nutritional components of protein bars

Per 35g bar, BRAIN PRO contains 190kcal of energy, 11.1g of protein, 13.5g of fat, 7.1g of carbohydrates (4.9g of sugars, 2.2g of dietary fiber), and 0.4g of salt equivalent. As mentioned above, when you assemble a diet with only plant-based foods, there is the effort of considering combinations because each food is low in different amino acids. BRAIN PRO is a bar that combines multiple plant-based protein sources, making it easy to incorporate as a snack when you are on the go or have a busy day. It is also recommended to incorporate it as a bar to easily supplement plant-based protein on days when you finish breakfast with only soy milk and bread, or when your lunch is likely to be just noodles. Because it does not use animal-based materials, it is also an easy option for those refraining from animal-based foods. After confirming the raw materials and nutritional labeling, see if it fits your diet.

Product	Content	Sugars	Artificial Sweeteners	White Sugar	Protein (Origin)
in Bar Protein Zakuzaku Choco	43g	11.7g	Not used	Used	17.9g / Soy, Milk
SAVAS Protein Bar Milk Chocolate Flavor	60g	Not displayed (10.4g sugars)	Used (Sucralose)	Used	23.7g / Milk, Soy
1-Pon Manzoku Bar Protein Strawberry	39g	9.4g	Used (Sucralose)	Used	16g / Soy, Milk
SOYJOY Calorie Control 80 Blueberry	17.8g	6.7g	Not used	Used	2.4g / Soy
BRAIN PRO	35g	4.9g	Not used	Not used	11.1g / Plant-based (Pea)

The figures for each product are based on nutritional information posted on the official websites of each manufacturer as of September 25, 2026. Figures may change due to product revisions.

Frequently Asked Questions

How many types of amino acids make up protein in the body?

The protein that builds the human body is made up of 20 types of amino acids. Among these, there are 9 types that cannot be synthesized in the body or are not synthesized in sufficient amounts and must be obtained through diet; these are called essential amino acids. Plant-based foods contain all 9 of these as well.

Are there differences in the types of plant-based protein depending on the food, like there are for animal-based?

Yes, there are. Different foods have different amino acids that are low in quantity; for example, grains like rice and wheat are low in lysine, while soy and legumes are low in sulfur-containing amino acids (methionine, cystine). Both can be supplemented by combining them with other foods.

Summary: How to take in plant-based protein and amino acids

In plant-based foods, the amino acids that are prone to deficiency differ between grains and legumes. Even if you don't strictly match them at every meal, if you eat grains and legumes in combination throughout the day, they become a combination that supplements each other. On days when you don't have the luxury of thinking about your menu, incorporating general foods that use plant-based protein is also one method. Check the raw material labeling and nutritional information labeling to choose something that fits your diet.