What are some low quality proteins?

December 1, 2025 •

4 min read

According to the Cleveland Clinic, most plant-based proteins are considered incomplete, meaning they are low in or lacking at least one of the nine essential amino acids. Understanding what are some low quality proteins is key to building a balanced diet that provides your body with all the necessary building blocks for muscle repair, tissue growth, and overall health. These proteins are often less bioavailable, which can impact your body's ability to absorb and utilize them effectively.

Quick Summary

Low quality proteins are typically incomplete, lacking one or more essential amino acids, and are found predominantly in plant sources like legumes and grains. Factors like biological value and digestibility determine protein quality, and options like processed meats may also be considered poor choices due to their processing methods. Combining incomplete proteins strategically is a proven method for acquiring a complete amino acid profile.

Key Points

Incomplete vs. Complete: Low quality proteins, often from plants, are 'incomplete' as they lack one or more essential amino acids, unlike 'complete' high quality proteins.
Plant-Based Sources: Common examples of incomplete proteins include legumes (beans, lentils), nuts, seeds, and most grains like rice and wheat.
Biological Value: Proteins with a lower biological value are less efficiently absorbed and utilized by the body compared to higher biological value proteins.
Processed Foods: Highly processed meats (bacon, hot dogs) and some protein bars contain low quality protein along with unhealthy additives like excessive sodium and saturated fat.
Combining for Completeness: You can create a complete amino acid profile by combining different incomplete proteins, such as rice with beans or hummus with pita.
Digestibility Matters: Digestibility is crucial for protein quality; generally, animal proteins are easier to digest than plant proteins, though cooking can improve the latter.

Understanding Protein Quality: The Role of Amino Acids

Protein quality is determined by two main factors: its amino acid profile and its digestibility. Our bodies need 20 different amino acids to function, nine of which are essential and must be obtained from food. A protein source is considered 'high quality' or 'complete' if it contains all nine essential amino acids in adequate proportions. Conversely, 'low quality' or 'incomplete' proteins are deficient in one or more of these essential amino acids. Most incomplete proteins come from plant-based sources, but some animal products can also be considered lower quality due to their processing. For individuals, especially those on vegetarian or vegan diets, understanding these differences is crucial for effective meal planning.

Incomplete Plant-Based Protein Sources

Many people mistakenly believe all plant proteins are automatically complete, but this is untrue. While still a valuable part of a healthy diet, most plant proteins need to be combined to provide a complete amino acid profile. The following list includes some common examples of plant-based low quality proteins:

Legumes: This category includes beans, peas, and lentils, which are often limited in the amino acid methionine.
Nuts and Seeds: Examples like peanuts, almonds, chia seeds, and sunflower seeds are incomplete. Peanut butter on whole wheat bread is a classic example of combining two incomplete proteins to form a complete one.
Grains: Wheat, rice, oats, and corn are incomplete, with most grains being deficient in lysine.
Certain Vegetables: While generally not a primary protein source, some vegetables like spinach and broccoli are considered to have a low biological value.

Low Quality Processed Protein Sources

Beyond incomplete amino acid profiles, protein quality can also be compromised by processing methods. Many processed meats, for instance, offer poor quality protein alongside high levels of saturated fat, sodium, and preservatives.

Processed Meats: Products like sausage, bacon, pepperoni, and hot dogs contain a small amount of poor-quality protein mixed with fillers and harmful additives.
Some Protein Bars: Many protein bars are highly processed and contain refined sugars and artificial ingredients that diminish their overall nutritional quality, despite their protein content.
Processed Yogurt: Some processed and flavored yogurts contain excessive sugar, making their protein content less beneficial to health.

The Concept of Biological Value and Digestibility

Biological Value (BV) is a measure of how efficiently the body can absorb and utilize a protein source. Digestibility refers to how well the body can break down the protein into its constituent amino acids. A protein with a higher BV is used more effectively than one with a lower BV. For example, animal proteins like eggs, meat, and dairy tend to have a higher BV and are more easily digestible than most plant proteins. However, cooking methods can impact the digestibility of plant proteins, often increasing it significantly. Some plant proteins, such as soy and quinoa, are exceptions and are considered complete proteins, but their overall digestibility can still be lower than animal-based alternatives.

Comparison of Low vs. High-Quality Proteins


Feature	Low Quality Proteins	High Quality Proteins
Amino Acid Profile	Incomplete; lacking one or more essential amino acids.	Complete; contains all nine essential amino acids.
Common Sources	Most plants (grains, legumes, nuts), some processed foods.	Animal products (meat, eggs, dairy), soy, quinoa.
Biological Value (BV)	Lower, meaning less efficient utilization by the body.	Higher, indicating more efficient utilization.
Digestibility	Often lower, especially in raw or unprocessed forms of plant proteins.	Generally higher, making for easier absorption.
Nutrient Density	Varies; can be high in other nutrients but requires pairing.	Often nutrient-dense, providing a complete profile in one source.

Complementary Proteins: Making the Most of Low-Quality Sources

For those relying on incomplete proteins, especially vegetarians and vegans, the key is protein complementation. This involves combining different incomplete protein sources to ensure all essential amino acids are consumed. Common examples of this practice include:

Rice and beans: Rice is low in lysine, while beans are rich in it. Combined, they provide a complete profile.
Hummus and pita: The chickpeas in hummus complement the amino acids in the pita bread.
Peanut butter on whole wheat bread: A classic combination where the nutrients from the nuts and grains balance each other.

It's important to note that you don't need to combine these proteins in a single meal. A varied diet throughout the day that includes different plant sources will provide all the essential amino acids you need.

Conclusion: Informed Choices for Optimal Health

Recognizing what constitutes a low quality protein is a foundational step toward more informed and conscious eating habits. While most animal sources are complete proteins, many plant-based sources are considered incomplete due to a missing or insufficient amount of one or more essential amino acids. The digestibility of a protein also plays a significant role in its overall quality. By understanding these concepts, you can make smarter dietary choices, whether that means prioritizing complete animal proteins or mastering the art of protein complementation with plant-based foods. A balanced, varied diet remains the best strategy for ensuring your body receives all the amino acids it needs to thrive.

Understanding protein quality and its impact on nutrition is essential for maximizing your diet's effectiveness.

Frequently Asked Questions

The main difference is the amino acid profile. High quality proteins contain all nine essential amino acids in sufficient amounts, while low quality proteins are lacking or have a limited amount of one or more essential amino acids.

No, not all plant-based proteins are low quality. The majority are incomplete, but some, like soy and quinoa, are exceptions and contain all nine essential amino acids, making them complete proteins.

No, you don't need to combine them at every single meal. A varied diet that includes a mix of different plant-based protein sources throughout the day will ensure you get all the essential amino acids your body needs.

Processed meats are often considered low quality because they contain a lower amount of protein relative to their calorie count and are loaded with preservatives, sodium, and unhealthy fats.

Protein digestibility affects how easily your body can break down and absorb the amino acids. A protein with low digestibility, like some plant sources, means your body won't be able to utilize all the amino acids effectively.

Yes, absolutely. Most incomplete proteins are part of highly nutritious foods like legumes and grains. The key is to consume a varied diet to ensure you receive a complete spectrum of amino acids over the course of the day.

Excellent examples of complete, high quality plant-based proteins include soy products (like tofu and edamame) and quinoa.