What is the difference between a high quality and low quality protein?

January 1, 2026 •

2 min read

Protein quality can vary significantly between different food sources, impacting your body's ability to utilize it effectively. Understanding the difference between a high quality and low quality protein is essential for optimizing muscle repair, growth, and overall health.

Quick Summary

Protein quality depends on its essential amino acid profile and digestibility. High-quality protein sources offer all nine essential amino acids and are easily absorbed, while low-quality sources are often incomplete and less digestible.

Key Points

Complete vs. Incomplete: High-quality protein contains all nine essential amino acids (complete), while low-quality protein is deficient in at least one (incomplete).
Digestibility Matters: High-quality protein is easily digested and absorbed by the body, typically with animal proteins having higher digestibility than plant proteins.
Source Examples: High-quality sources include eggs, meat, dairy, soy, and quinoa. Low-quality sources include most other grains, legumes, and nuts.
Combine for Completeness: Plant-based diets can achieve a complete protein profile by combining different incomplete protein sources throughout the day, like rice and beans.
Muscle Repair: High-quality protein is especially beneficial for muscle growth and repair after exercise due to its amino acid profile, including the key amino acid leucine.

The Fundamental Difference: Amino Acid Profile

Protein is composed of amino acids, with nine being essential and requiring dietary intake. A high-quality protein, or complete protein, provides all nine essential amino acids in sufficient amounts. A low-quality protein, or incomplete protein, lacks one or more essential amino acids. Grains, for instance, are often low in lysine, while legumes may be limited in methionine. The limiting amino acid restricts the body's capacity to synthesize new proteins.

The Role of Digestibility and Absorption

Digestibility also determines protein quality, indicating how effectively the body breaks down, absorbs, and uses protein. Animal proteins are highly digestible (90-100%). Plant proteins are generally less digestible (60-90%) due to fiber and anti-nutritional factors that hinder absorption.

How Protein Quality is Measured

The Digestible Indispensable Amino Acid Score (DIAAS) is now the recommended method for assessing protein quality, replacing the older PDCAAS.

DIAAS vs. PDCAAS: DIAAS provides a more accurate measure of human digestion by assessing ileal amino acid digestibility. It also offers scores above 100%, better differentiating high-quality proteins than PDCAAS, which caps scores at 100%.

Combining Incomplete Proteins

Individuals following plant-based diets can achieve a complete protein intake by combining complementary proteins. Different incomplete proteins have different limiting amino acids, and combining them over the day ensures all nine essential amino acids are consumed.

Complementary Protein Combinations:
- Rice and beans
- Whole wheat bread and peanut butter
- Lentils and whole grains
- Hummus and whole-grain pita bread
- Tofu and vegetables

Benefits of Prioritizing High-Quality Protein

Consuming high-quality protein consistently offers several health benefits.

Muscle Growth and Repair: High-quality protein supports muscle protein synthesis after exercise by providing essential amino acids, particularly leucine.
Increased Satiety: Protein promotes fullness, aiding appetite control and weight management.
Metabolic Function: The body expends more energy to digest protein compared to other macronutrients.
Bone Health: Adequate protein intake contributes to bone density and strength.

Comparison Table: High Quality vs. Low Quality Protein


Feature	High Quality Protein	Low Quality Protein
Amino Acid Profile	Contains all nine essential amino acids (complete).	Deficient in one or more essential amino acids (incomplete).
Digestibility	Highly digestible (90-100%).	Less digestible (60-90%).
Source Examples	Animal products (eggs, dairy, meat, fish), soy, quinoa.	Most plant foods (grains, legumes, nuts), unless combined.
Nutritional Density	Often nutrient-dense, especially for muscle repair.	May require combining for a complete amino acid profile.

Conclusion

High-quality protein is defined by its complete essential amino acid profile and high digestibility. While animal sources are typically high-quality, plant-based diets can meet these needs by combining various protein sources. A diverse diet incorporating different protein types ensures the body receives all necessary amino acids for optimal health.

For more detailed information on protein requirements and quality assessment methods, consult the official FAO guidelines on Dietary protein quality evaluation in human nutrition.

Frequently Asked Questions

The primary difference lies in the amino acid profile. High-quality protein contains all nine essential amino acids in adequate amounts, while low-quality protein is missing or low in one or more of these essential amino acids.

Most animal proteins, such as those from meat, dairy, and eggs, are considered high-quality because they are complete proteins and are highly digestible. An exception is gelatin, which is an incomplete protein.

Yes. While many plant proteins are incomplete on their own, a variety of plant-based foods can be combined to provide all essential amino acids. Examples include pairing grains with legumes, like rice and beans.

A limiting amino acid is the essential amino acid present in the lowest quantity within a food relative to the body's needs. If this amino acid is insufficient, it can limit the body's ability to synthesize new proteins.

For optimal health, consume a varied diet rich in different protein sources. For meat-eaters, a mix of animal and plant proteins is ideal. For those on a plant-based diet, strategically combine different foods like grains, legumes, nuts, and seeds throughout the day.

Yes, some cooking and processing methods can alter a protein's structure, potentially affecting its digestibility and how easily your body can absorb its amino acids. However, other methods can sometimes improve digestibility.

The benefits include improved muscle growth and repair, increased feelings of fullness (satiety), support for metabolic function, and better bone health. High-quality protein is especially crucial for athletes or those trying to build muscle.