Which Beans Have All 9 Amino Acids? Discovering Complete Plant Proteins

November 13, 2025 •

4 min read

Over 90% of American females and 97% of American males do not get the recommended amount of fiber, a common nutrient found alongside protein in many beans. For those seeking complete plant-based proteins, a key question is: which beans have all 9 amino acids? The simple answer is that soybeans are a notable exception among beans, containing all nine essential amino acids.

Quick Summary

Soybeans and products like edamame and tofu are considered complete proteins, containing all nine essential amino acids. Most other beans are incomplete, lacking certain amino acids, but can be paired with grains to form a complete protein meal. This article details the specific characteristics of soybeans and outlines strategies for combining other legumes for a balanced plant-based diet.

Key Points

Soybeans are a complete protein: They are the only true bean that provides all nine essential amino acids, making them a unique plant-based option.
Most beans are incomplete proteins: Common beans like kidney, black, and pinto beans lack sufficient levels of certain essential amino acids, such as methionine and cysteine.
Complementary proteins are effective: You can achieve a complete amino acid profile by pairing beans with grains (e.g., rice and beans), seeds, or nuts throughout the day.
Quinoa is another complete plant protein: Though technically a seed, quinoa is a pseudocereal that also provides all nine essential amino acids.
Soy products retain the complete protein: Edamame, tofu, tempeh, and soy milk all offer the same complete protein benefit as whole soybeans.
Variety is key for vegans: A diverse plant-based diet naturally provides all essential amino acids, so strict meal-by-meal combining is not necessary.

Understanding Complete Proteins and Amino Acids

Protein is a crucial macronutrient composed of smaller organic compounds called amino acids. There are 20 different amino acids, but the human body can only produce 11 of them. The other nine, known as essential amino acids, must be obtained through dietary sources. A 'complete protein' is any food that contains all nine of these essential amino acids in sufficient quantities. While animal products are classic examples of complete proteins, the plant-based world offers options as well, with soybeans being a prime example.

The Star Player: Soybeans

Soybeans (Glycine max) are the standout among beans, offering a complete protein profile comparable to that of animal protein. Their high protein content is a significant reason for their widespread use in vegan and vegetarian diets. Foods derived from soybeans, such as tofu, tempeh, and edamame, are all excellent sources of complete protein. The fermentation process used to create tempeh and the coagulation of soy milk for tofu retain the full spectrum of essential amino acids. A single half-cup serving of shelled edamame can provide over 15 grams of protein, making it an extremely potent source. This makes soybeans and their derivatives a highly convenient and efficient way for vegans and vegetarians to meet their essential amino acid requirements.

The Importance of Complementary Proteins

While soybeans are unique, most other beans are considered 'incomplete' proteins because they lack sufficient amounts of one or more essential amino acids. However, this is not a major obstacle for a balanced plant-based diet. Nutritionists previously suggested that different incomplete protein sources needed to be eaten together in the same meal to form a complete protein. Current understanding is more relaxed; as long as a variety of plant proteins are consumed throughout the day, the body can combine the amino acid pools to get everything it needs. For example, legumes are typically high in lysine but low in methionine, whereas grains are the opposite. Combining rice and beans is a classic, culturally ingrained example of this complementary protein strategy.

Combining Beans and Other Plant Foods for a Complete Profile

To ensure all essential amino acids are consumed, a well-rounded diet is key. Here are some effective and delicious pairing strategies:

Beans with Grains: The classic combination of rice and beans is a complete protein powerhouse. This includes dishes like red beans and rice, black beans and tortillas, or lentil soup with whole-grain bread.
Legumes with Nuts or Seeds: Hummus is a perfect example, combining chickpeas (a legume) with sesame seeds (a seed-based tahini). Similarly, a salad with chickpeas and sunflower seeds provides a full amino acid profile.
Whole Grains with Other Legumes: Besides soybeans, other pseudo-cereals like quinoa and buckwheat are also notable for containing all nine essential amino acids. Adding these to meals with other beans or lentils further enriches the amino acid intake.
Nutritional Yeast: For those who need a concentrated supplement, nutritional yeast can be a complete protein source, and it adds a savory, cheesy flavor to dishes.

Comparative Protein Profiles of Beans

To highlight the difference between soybean and other common beans, the following table compares their protein and amino acid profiles. The data illustrates why soybeans stand out as a 'complete' protein source on their own, while others require pairing for a full profile.


Bean Type (cooked, per 1/2 cup)	Protein Content (g)	Complete Protein?	Complementary Food Pairings
Soybeans (Edamame)	15.7	Yes	N/A (already complete)
Lentils	8.9	No	Grains (like rice) for methionine and cysteine
Kidney Beans	7.7	No	Grains (like corn) for methionine
Black Beans	7.6	No	Grains (like rice) for methionine and cysteine
Chickpeas	7.3	No	Grains (like bread) or sesame seeds (tahini)
Navy Beans	7.5	No	Grains (like wheat bread)

The Role of Soy in a Balanced Diet

Soybeans and soy products have been consumed for millennia and are well-regarded for their nutritional benefits. They are not only a complete protein but also contain significant amounts of essential fatty acids, vitamins, and minerals. The high fiber content found in soy foods is beneficial for digestive health and can help regulate blood sugar levels. Despite some historical misconceptions and debates, the vast majority of research supports soy as a healthy and safe component of a balanced diet for most people. For those concerned about sourcing, it is worth noting that a large percentage of conventionally produced soybeans are genetically modified. Opting for organic, non-GMO soy products can address this concern for consumers. To learn more about protein requirements and nutrition, a reliable resource is the Harvard T.H. Chan School of Public Health's nutrition source.

Conclusion

In summary, the specific bean that contains all nine essential amino acids is the soybean. While most other beans and legumes are considered 'incomplete' proteins, this does not make them inferior sources of nutrition. Through the simple and effective strategy of complementary pairing with grains, seeds, or nuts, all the necessary amino acids can be obtained. Embracing a varied, plant-based diet that includes soybeans, lentils, and other protein-rich plants ensures a comprehensive and balanced intake of all essential amino acids, supporting overall health and well-being.

Frequently Asked Questions

No, black beans are not a complete protein source on their own. They lack adequate amounts of certain essential amino acids, but can be paired with a grain like rice to form a complete protein meal.

Yes, you can easily get all essential amino acids on a vegan diet by consuming a variety of plant-based protein sources throughout the day, including soybeans and complementary pairings like rice and beans.

A complete protein contains all nine essential amino acids that the body cannot produce itself. An incomplete protein lacks one or more of these essential amino acids.

For most people, soybeans are a safe and nutritious food. Some concerns exist regarding GMOs and antinutrients, but proper cooking and preparation significantly reduce these effects for healthy individuals.

Yes, hummus is generally considered a complete protein because it is made from a combination of chickpeas (a legume high in lysine) and tahini (a paste made from sesame seeds, which provides other necessary amino acids).

Other complete plant-based proteins include quinoa, buckwheat, and hemp seeds.

A half-cup of cooked soybeans (edamame) has about 15.7 grams of protein, nearly double the amount found in the same serving size of many other common beans.