What are some examples of incomplete proteins? A comprehensive guide

January 12, 2026 •

4 min read

Over 90% of plant-based protein sources are considered incomplete, meaning they lack or are low in one or more of the nine essential amino acids. Understanding what are some examples of incomplete proteins is crucial for building a well-rounded and nutrient-dense diet, especially for those following vegetarian or vegan eating patterns.

Quick Summary

Incomplete proteins lack one or more essential amino acids but can be combined to form a complete profile. Common examples include most plant-based foods like grains, legumes, nuts, and seeds. Varying your intake of these foods throughout the day ensures you get all the necessary amino acids.

Key Points

Legumes are incomplete: Beans, lentils, and peas are all examples of incomplete proteins, meaning they lack or are low in at least one essential amino acid.
Grains are incomplete: Foods like rice, oats, and wheat are incomplete proteins, but they can be combined with legumes to form a complete amino acid profile.
Nuts and seeds vary: While many nuts and seeds are incomplete, some, like chia and hemp, are nearly complete, though some essential amino acids may be low.
Combining isn't necessary at every meal: You do not need to combine specific incomplete proteins at every meal; your body stores amino acids throughout the day.
Variety is key: A varied diet that includes a wide range of plant-based foods is the most effective way to ensure you receive all essential amino acids.
Soy, quinoa, and buckwheat are exceptions: These plant-based foods are considered complete proteins, containing all nine essential amino acids.

Understanding Incomplete vs. Complete Proteins

Proteins are the building blocks of the human body, composed of smaller units called amino acids. There are 20 amino acids in total, but nine of these are considered 'essential' because our bodies cannot produce them and must obtain them from food.

Complete Proteins: These contain all nine essential amino acids in sufficient amounts. Animal-based products like meat, poultry, fish, eggs, and dairy are classic examples. Some plant-based foods like soy, quinoa, and buckwheat are also complete proteins.
Incomplete Proteins: These lack or are deficient in one or more of the essential amino acids. The vast majority of plant-based protein sources fall into this category. The good news is that you don't need to consume all essential amino acids at every single meal. By eating a varied diet with different plant foods throughout the day, your body can draw from a stored 'pool' of amino acids to form complete proteins.

Examples of Incomplete Protein Food Groups

The following plant-based food groups are all excellent sources of nutrition but are considered incomplete proteins. Combining different types can help ensure a balanced intake of all essential amino acids.

Legumes

Legumes are a cornerstone of plant-based diets, typically containing all essential amino acids but being low in methionine.

Beans: Black beans, kidney beans, pinto beans, and chickpeas are all common examples. They are rich in lysine but need to be paired with grains to provide methionine.
Lentils: A staple in many cuisines, lentils are a great source of protein and fiber but are also limited in methionine.
Peas: This includes green peas and split peas. Like other legumes, they are lysine-rich but need a complementary source of methionine.

Grains

Most grains are limited in the essential amino acid lysine but contain sufficient methionine, which complements the amino acid profile of legumes.

Wheat: Found in bread, pasta, and other baked goods. Whole-wheat bread with peanut butter is a classic complementary pairing.
Rice: Both brown and white rice are incomplete proteins. The traditional pairing of rice and beans is a complete protein powerhouse.
Oats: Excellent for breakfast, oats are an incomplete protein that can be complemented by adding seeds or nuts.

Nuts and Seeds

Nuts and seeds offer healthy fats and protein but are generally incomplete on their own. Many are low in lysine or methionine.

Almonds: A popular snack that is an incomplete protein.
Walnuts: Also an incomplete protein source.
Seeds: Pumpkin seeds, sunflower seeds, and chia seeds are examples. Chia seeds and hemp seeds are often cited as being nearly complete, but their amino acid levels are still low enough in some areas (e.g., lysine) that they are not considered truly complete by all experts.

Vegetables

While not the primary source of protein, vegetables contribute to overall intake and are incomplete on their own.

Broccoli, spinach, and kale: These leafy greens and cruciferous vegetables contain protein but not a complete profile.
Corn: Corn is low in the essential amino acid tryptophan.

The Power of Complementary Proteins

The most effective way to ensure a sufficient intake of all essential amino acids on a plant-based diet is through complementary proteins. This involves combining different incomplete protein sources throughout the day. It is a misconception that these foods must be eaten together in the same meal. A varied diet ensures your body receives all necessary amino acids from its daily intake.

Here are some classic examples of complementary protein pairings:

Rice and beans: The lysine in the beans complements the methionine in the rice, creating a complete protein.
Peanut butter on whole-wheat bread: The lysine in the peanuts complements the methionine in the whole-wheat grain.
Hummus and pita bread: The chickpeas in hummus provide lysine, while the wheat in the pita bread offers the necessary methionine.
Lentil soup with a whole-grain roll: Another great example of pairing a legume with a grain.

Complete vs. Incomplete Proteins Comparison Table


Feature	Complete Proteins	Incomplete Proteins
Essential Amino Acids	Contains all nine essential amino acids in adequate amounts.	Lacks or is low in one or more essential amino acids.
Common Sources	Animal products (meat, eggs, dairy), soy, quinoa, buckwheat.	Most plant-based foods (legumes, grains, nuts, seeds, vegetables).
Dietary Importance	Provides all building blocks in one source, often favored by athletes and those with specific needs.	Requires a variety of sources throughout the day to ensure all essential amino acids are consumed.
Combination Necessity	Not necessary to combine with other proteins to obtain all essential amino acids.	Needs to be combined with complementary proteins to create a complete amino acid profile.
Example Pairing	Single food item (e.g., chicken breast, eggs).	Combining two food items (e.g., rice and beans, hummus and pita).

Conclusion

While a large number of plant-based foods are technically incomplete proteins, this is not a cause for concern for most people. The outdated advice to combine specific foods in a single meal to form a complete protein has been widely debunked. A varied diet that includes a mix of legumes, grains, nuts, and seeds throughout the day provides all the necessary essential amino acids. Eating a diverse range of foods also offers a broader spectrum of other vital nutrients, such as fiber, vitamins, and minerals, which contributes to overall health and well-being. For more information on dietary guidelines, consult the National Institutes of Health.(https://pmc.ncbi.nlm.nih.gov/articles/PMC7760812/)

For those on a plant-based diet, focusing on variety rather than complex food pairing is the simplest and most effective strategy. Enjoying dishes like lentil soup with a slice of whole-grain bread, or a salad with chickpeas and sunflower seeds, ensures you get all the protein building blocks you need without overthinking every meal. Both complete and incomplete proteins have a valuable place in a healthy diet, so the key is balance and diversity.

Frequently Asked Questions

An incomplete protein is a food source that does not contain all nine of the essential amino acids that your body needs but cannot produce on its own. Most plant-based proteins fall into this category.

Common examples of incomplete protein foods include legumes (beans, lentils, peas), grains (rice, wheat, oats), nuts (almonds, walnuts), and most vegetables.

You can make an incomplete protein complete by combining it with another incomplete protein source that has the missing amino acid. For example, pairing grains with legumes, like rice and beans, creates a complete protein.

No, this is a myth. The body maintains a pool of amino acids from various foods eaten throughout the day. By consuming a variety of plant-based foods, you can easily get all essential amino acids without specific meal-time combinations.

A few exceptions to the rule exist. Soy products (tofu, tempeh), quinoa, buckwheat, and chia seeds are considered complete or nearly complete proteins.

No, incomplete proteins are not unhealthy. Many are incredibly nutrient-dense, providing fiber, vitamins, minerals, and antioxidants. A varied diet of incomplete proteins can be just as healthy as a diet with complete proteins.

Legumes like beans and lentils are incomplete proteins primarily because they are low in the essential amino acid methionine. They are, however, rich in lysine, making them a perfect complement to grains.