What is the meaning of high quality protein?

November 27, 2025 •

4 min read

According to the FAO/WHO, protein quality is determined by the capacity of a protein to provide an adequate quantity of nitrogen and all nine indispensable amino acids. This critical nutrient is vital for health, but not all protein is created equal, making it important to understand the meaning of high quality protein.

Quick Summary

High-quality protein is determined by a complete essential amino acid profile and high digestibility. Animal proteins and some plant sources like soy and quinoa are considered superior due to their amino acid balance and efficient absorption. Protein quality is measured using scoring systems like PDCAAS and the more advanced DIAAS.

Key Points

Complete Amino Acid Profile: High-quality proteins, or "complete" proteins, contain all nine essential amino acids that the body cannot produce on its own.
High Digestibility: Protein quality is significantly influenced by how efficiently the body can digest and absorb its amino acids. Animal proteins generally have higher digestibility than plant proteins.
DIAAS vs. PDCAAS: Newer and more accurate scoring methods like DIAAS (Digestible Indispensable Amino Acid Score) use ileal digestibility and are not capped, providing a clearer ranking of protein quality than the older PDCAAS.
Diverse Sources are Key: You don't need all complete proteins in one meal. By consuming a variety of different protein sources throughout the day, you can meet all your essential amino acid needs.
Health Benefits: A diet rich in high-quality protein supports muscle growth, weight management through increased satiety, enhanced metabolic rate, and stronger bones.
Inclusion of Plant and Animal Proteins: A balanced diet combining both animal-based (meat, eggs, dairy) and high-quality plant-based proteins (soy, quinoa) offers a complete nutritional package.

What Defines a High-Quality Protein?

At its core, a protein's quality is defined by two primary factors: its amino acid profile and its digestibility. Proteins are made up of building blocks called amino acids, and of the 20 found in nature, nine are considered essential. This means the human body cannot produce them and must obtain them through diet. A high-quality protein, also known as a 'complete' protein, contains all nine of these essential amino acids in sufficient quantities and proportions to support the body's needs.

The second critical factor is digestibility. A protein's nutritional value is only as good as the body's ability to break it down, absorb its amino acids, and utilize them. Animal-based proteins like meat, eggs, and dairy are typically highly digestible. Plant-based proteins, on the other hand, can be less digestible due to their fibrous structures and the presence of anti-nutritional factors, though processing methods can improve this.

The Importance of Essential Amino Acids

Essential amino acids (EAAs) are the benchmark for a protein's completeness. If a protein source is low or lacking in even one EAA, it becomes a 'limiting amino acid,' restricting the body's ability to synthesize new proteins effectively. This can compromise muscle building, tissue repair, and other vital functions. Fortunately, the classic concept of needing to perfectly 'complement' incomplete proteins at every single meal is outdated. The body can store EAAs in a metabolic pool throughout the day, allowing for flexibility in dietary choices. As long as you consume a variety of protein sources, you can meet all your EAA needs.

How Protein Quality is Measured: PDCAAS vs. DIAAS

Nutrition scientists use standardized scoring methods to quantify and compare protein quality. The two most prominent are the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and the newer Digestible Indispensable Amino Acid Score (DIAAS).

Protein Digestibility-Corrected Amino Acid Score (PDCAAS):

Adopted by the FDA in 1993, PDCAAS evaluates protein quality based on both the amino acid profile and a correction for fecal digestibility.
The score is capped at 1.0, meaning several different high-quality proteins can all receive the same top score, limiting comparative usefulness.
Animal proteins like casein, whey, and egg, along with isolated soy protein, typically receive a score of 1.0.

Digestible Indispensable Amino Acid Score (DIAAS):

Introduced by the Food and Agriculture Organization of the United Nations (FAO) in 2013, DIAAS is a more accurate measure.
Instead of fecal digestibility, it uses ileal digestibility, which more precisely measures the amino acids absorbed in the small intestine before they are potentially utilized by gut bacteria.
DIAAS values are not capped at 1.0, allowing for a clearer differentiation between truly superior protein sources.
This metric is becoming the new standard in nutritional science.

Comparing Animal and Plant Protein Sources

Understanding the meaning of high quality protein is essential when evaluating different sources. While animal-based proteins generally have a higher biological value and digestibility, many plant sources are also excellent when consumed as part of a varied diet.


Feature	Animal Protein Sources	Plant Protein Sources
Amino Acid Profile	Complete, containing all nine EAAs in optimal ratios.	Many are incomplete, lacking sufficient quantities of one or more EAA, though soy and quinoa are notable exceptions.
Digestibility	Typically very high (90-99%), allowing for efficient absorption.	Can be lower due to fiber and anti-nutritional factors, but can be improved through processing.
Nutrient Density	Often comes with vital nutrients like iron, B12, and creatine, but can also contain higher saturated fat.	Often richer in fiber, vitamins, and minerals. Typically lower in saturated fat.
Health Impact	Can be associated with higher saturated fat intake depending on the cut and processing, potentially impacting cardiovascular health.	Linked to improved health outcomes, including lower risk of chronic diseases and better gut health.

Health Benefits of High-Quality Protein

Incorporating high-quality protein into your diet provides significant health advantages:

Muscle Maintenance and Growth: High-quality protein supplies the body with the full range of amino acids needed to build and repair muscle tissue, crucial for both athletes and aging individuals.
Satiety and Weight Management: Protein-rich foods promote a feeling of fullness, which can reduce overall calorie intake and assist in weight loss and management.
Bone Health: Research suggests adequate protein intake, particularly from animal sources, may play a crucial role in maintaining bone density and reducing the risk of osteoporosis, especially when combined with resistance exercise.
Metabolic Boost: The thermic effect of food (TEF) is highest for protein, meaning your body burns more calories digesting it compared to carbohydrates or fats, which can increase your metabolic rate.
Improved Recovery: For individuals recovering from injury or surgery, high-quality protein is essential for the growth, renewal, and healing of cells and tissues.

Conclusion

The meaning of high quality protein extends beyond just its quantity. It's a combination of a complete essential amino acid profile and high digestibility, which determine how effectively the body can use the protein. While animal products and specific plant sources like soy and quinoa are excellent choices, a varied diet that includes a range of both animal and plant-based foods can provide all the necessary essential amino acids. Evaluating protein quality through metrics like DIAAS can offer a more nuanced understanding, but the key takeaway for most people is to focus on a diverse and balanced intake of nutrient-dense protein sources. This approach not only supports muscle, bone, and overall health but can also assist with weight management and recovery.

For more information on protein metabolism and human requirements, consult Dietary protein quality evaluation in human nutrition by the Food and Agriculture Organization of the United Nations (FAO).

Frequently Asked Questions

The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. They must be obtained from dietary sources because the human body cannot synthesize them.

Most animal proteins like meat, poultry, fish, eggs, and dairy are considered high-quality due to their complete essential amino acid profile and high digestibility. However, certain cuts of meat can also be high in unhealthy saturated fats.

No, not all plant proteins are low-quality. While many plant proteins are considered 'incomplete' because they are low in one or more essential amino acids, sources like soy and quinoa contain all nine essential amino acids, making them high-quality.

Yes, it is entirely possible for vegetarians and vegans to meet their high-quality protein needs by consuming a variety of plant-based protein sources throughout the day, such as soy products, legumes, nuts, seeds, and whole grains.

A complete protein simply contains all nine essential amino acids. High-quality protein includes not only a complete amino acid profile but also considers the protein's digestibility, meaning how efficiently the body can absorb and use its amino acids.

Protein digestibility is important because it determines how many amino acids from a food source can be utilized by the body after digestion and absorption. A protein with a poor digestibility score will not be as effective, regardless of its amino acid profile.

You can combine various plant proteins to ensure you consume all essential amino acids throughout the day. Classic examples include rice and beans, peanut butter on whole wheat bread, or hummus with pita.