Which type of protein does not provide all of the essential amino acids?

December 28, 2025 •

3 min read

According to nutrition experts, a protein source is considered "incomplete" when it is lacking in one or more of the nine essential amino acids. This is the type of protein that does not provide all of the essential amino acids, and it is most commonly found in plant-based foods.

Quick Summary

An incomplete protein lacks one or more of the nine essential amino acids and is mainly sourced from plant foods. It can be made complete by combining various plant proteins throughout the day, a process known as protein complementation.

Key Points

Incomplete Proteins Lack Essential Amino Acids: Found mainly in plant sources like legumes, grains, and nuts, incomplete proteins are deficient in one or more of the nine essential amino acids.
Complete Proteins Have All Nine Essential Amino Acids: Animal sources (meat, dairy, eggs) and a few plant sources (soy, quinoa, buckwheat) are considered complete proteins because they contain all essential amino acids.
Protein Complementation Creates a Complete Profile: Combining different incomplete protein sources, like rice and beans, provides all essential amino acids over the course of a day.
Dietary Variety is Key for All Diets: Consuming a wide range of foods, whether animal-based or plant-based, ensures adequate intake of all amino acids and other vital nutrients.
Plant Proteins Offer Unique Health Benefits: Incomplete proteins from plant sources are often high in fiber, antioxidants, and beneficial phytochemicals, promoting gut health and reducing disease risk.

Understanding the difference between complete and incomplete proteins

To understand which type of protein does not provide all of the essential amino acids, it's necessary to first grasp the distinction between 'complete' and 'incomplete' proteins. The human body requires 20 different amino acids to function properly, but can only produce 11 of them on its own. The remaining nine—known as essential amino acids—must be obtained through diet.

Complete Proteins: Contain all nine essential amino acids in sufficient quantities. Animal products like meat, fish, poultry, eggs, and dairy are classic examples. Some plant-based foods, such as soy, quinoa, and buckwheat, are also considered complete proteins.
Incomplete Proteins: Do not contain adequate levels of one or more of the essential amino acids. The majority of plant-based protein sources fall into this category. They are not "bad" or "unhealthy," but simply require pairing with other protein sources to ensure all essential amino acids are consumed.

The role of incomplete proteins in a balanced diet

Incomplete proteins are the building blocks of a healthy, varied diet, especially for those following a vegetarian or vegan lifestyle. While no single incomplete protein source offers a full amino acid profile, consuming a variety of these foods throughout the day, rather than in a single meal, is sufficient to meet your body's needs. This strategic pairing is often called protein complementation.

For example, legumes are often limited in the amino acid methionine, while grains can be low in lysine. By combining them, as in the classic dish of rice and beans, you create a complete protein. Your body has a pool of amino acids it can draw from, so these complementary foods don't need to be eaten at the exact same time.

Why dietary variety is so important

Eating a wide variety of foods from different groups is crucial for overall health, beyond just ensuring a complete protein intake. Different foods offer unique combinations of nutrients, vitamins, minerals, and fiber that work together synergistically. This practice reduces the risk of nutrient deficiencies and provides a broader range of antioxidants and phytochemicals. For plant-based eaters, this variety is essential for obtaining all nine essential amino acids and other critical nutrients like iron, B vitamins, and healthy fats.

Comparison of complete vs. incomplete protein sources


Feature	Complete Proteins	Incomplete Proteins
Essential Amino Acids	Contain all nine in sufficient amounts.	Lack or are low in one or more essential amino acids.
Common Sources	Meat, fish, poultry, eggs, dairy, soy, quinoa, buckwheat.	Legumes, nuts, seeds, grains, vegetables.
Example Combinations	N/A	Rice and beans, hummus and pita, peanut butter sandwich.
Nutrient Density	Often rich in B12, iron, and zinc, but can be high in saturated fat.	Typically higher in fiber, antioxidants, and beneficial phytochemicals.
Digestibility	Generally more easily and completely absorbed by the body.	May contain antinutrients that can slightly reduce absorption, though still beneficial.
Dietary Strategy	Simple, as a single source provides all essential amino acids.	Requires mindful combining of different sources over the day.

Making smart protein choices

Regardless of your dietary preferences, it is entirely possible to meet all your protein requirements. For omnivores, incorporating a variety of protein sources, including lean meats, fish, and a mix of plants, is the most straightforward approach. If you follow a plant-based diet, focusing on variety is the key to nutritional success. This mindful approach ensures you benefit from a wide array of nutrients and fiber that are abundant in plants, while still covering all your essential amino acid bases. The outdated notion that vegans must combine proteins perfectly in every meal has been debunked; what is more important is a varied diet over the course of a day. By understanding the sources and qualities of both incomplete and complete proteins, you can make informed decisions that support a healthy lifestyle.

Conclusion: The importance of variety

To summarize, incomplete proteins are the type that do not provide all of the essential amino acids individually. Found predominantly in plant-based foods like legumes, grains, and nuts, they can be successfully combined with other plant foods to form a complete amino acid profile. The key takeaway is not that incomplete proteins are inferior, but that a diverse and varied diet is crucial for both omnivores and plant-based eaters to receive the full spectrum of essential amino acids and other vital nutrients for optimal health. A well-planned, whole-foods, plant-based diet can be a powerful tool for weight management and reducing the risk of chronic diseases.

Frequently Asked Questions

An incomplete protein is a food source that is low in or missing one or more of the nine essential amino acids required by the human body.

Common examples of incomplete proteins include legumes (beans, lentils), nuts, seeds, most grains (except quinoa and buckwheat), and many vegetables.

Yes, vegetarians and vegans can get enough protein by eating a wide variety of plant-based foods. The body's amino acid pool can draw from different foods consumed throughout the day to meet all essential amino acid needs.

Protein complementation is the practice of combining two or more incomplete protein sources that, together, provide all nine essential amino acids. Classic examples include rice and beans or hummus and pita bread.

No, complementary proteins do not need to be eaten in the same meal. As long as a variety of protein sources are consumed throughout the day, the body's needs for all essential amino acids will be met.

No, the term 'incomplete' does not mean less healthy. Incomplete protein sources, like many plant foods, are often rich in other beneficial nutrients such as fiber, vitamins, and antioxidants.

While most plant proteins are incomplete, some notable exceptions that contain all nine essential amino acids include quinoa, soy products (tofu, tempeh), buckwheat, and hemp seeds.