Understanding Protein Quality: What is the efficiency of a protein called?

October 22, 2025 •

3 min read

While many think of protein simply by its quantity, its true value is measured by its biological impact. The complex answer to the question, "What is the efficiency of a protein called?" involves multiple metrics, with the modern standard being DIAAS.

Quick Summary

Protein efficiency is assessed through various evolving metrics like DIAAS, PDCAAS, Biological Value, and PER, which measure how effectively the body absorbs and uses protein based on its amino acid profile and digestibility.

Key Points

No Single Name: There is no single term for protein efficiency; it is measured by several scientific metrics that have evolved over time, such as PER, BV, PDCAAS, and DIAAS.
DIAAS is the Modern Standard: The Digestible Indispensable Amino Acid Score (DIAAS) is the most recommended modern metric for assessing protein quality, offering superior accuracy by measuring ileal digestibility.
Older Methods Were Flawed: Historical methods like the Protein Efficiency Ratio (PER) had limitations, such as being based on animal weight gain and failing to account for maintenance requirements.
Digestibility is Crucial: A key factor in efficiency is how well the body digests and absorbs individual amino acids. DIAAS provides a more accurate measure of this than its predecessor, PDCAAS.
Limiting Amino Acids Matter: The overall quality of a protein source is determined by the most deficient indispensable amino acid in its profile.
Food Combinations Enhance Efficiency: Combining different protein sources, such as complementary proteins like legumes and cereals, can create a more complete and efficient amino acid profile.
Processing Can Affect Quality: Heat and other food processing methods can either improve or diminish a protein's efficiency by affecting digestibility or damaging sensitive amino acids.

The Multiple Names for Protein Efficiency

There is no single term for the efficiency of a protein because its measurement has evolved over time with scientific understanding. The true efficiency of a protein depends on its amino acid profile, digestibility, and how the body ultimately utilizes it. Protein quality hinges on both amino acid composition and digestibility. A high-quality protein has all nine indispensable (essential) amino acids in beneficial proportions and is easily absorbed.

The Evolution of Protein Scoring

Over the past century, various methods have been developed to measure protein efficiency, with each new system aiming to improve upon its predecessor. These methods transitioned from animal-based assays to more precise chemical scores tailored for human nutrition.

Early Methods: PER and Biological Value

The Protein Efficiency Ratio (PER) was an early method used from 1919 until the early 1990s, based on the weight gain of growing rats. It is criticized for not accounting for maintenance needs, including fat gain in weight measurements, and using rat requirements which differ from humans. Biological Value (BV) measures the proportion of absorbed protein retained by the body, based on nitrogen balance, but doesn't account for protein that wasn't absorbed in the first place. Net Protein Utilization (NPU) combines BV with digestibility (NPU = BV x Digestibility), offering a more complete measure than BV alone, though still often based on animal models.

PDCAAS: The Former Standard

Adopted by the FDA in 1993, the Protein Digestibility Corrected Amino Acid Score (PDCAAS) compared a protein's amino acid profile to an ideal human pattern and corrected it for fecal digestibility. Its calculation involves the amino acid score multiplied by true fecal digestibility. However, PDCAAS has two main criticisms: scores are capped at 1.0, not fully reflecting superior proteins, and it uses fecal digestibility, which is less accurate for human use than ileal digestibility.

DIAAS: The Modern Approach

The Digestible Indispensable Amino Acid Score (DIAAS), recommended by the FAO in 2013, is considered the new standard. DIAAS offers a more precise measure by using true ileal digestibility, assessing amino acid absorption at the end of the small intestine before bacterial impact. It also scores individual amino acids, uses specific reference patterns for different age groups, and importantly, does not truncate scores above 100%. DIAAS represents a significant advancement in accurately assessing protein efficiency.

Comparing Protein Scoring Methods

The evolution of protein metrics highlights the effort to find the most accurate measure of efficiency. Here's a brief comparison:


Feature	PER	BV	PDCAAS	DIAAS
Core Principle	Weight gain relative to protein intake (rats)	Nitrogen retained relative to nitrogen absorbed	Limiting amino acid score corrected for fecal digestibility	Limiting amino acid score corrected for ileal digestibility
Digestibility Metric	Not measured	Not included in BV score	True fecal digestibility (rat assay)	True ileal digestibility (pig/human assay)
Score Truncation	No	No	Yes, capped at 1.0	No, score can be >100%
Model	Growing rats	Nitrogen balance in humans/animals	Growing rats	Primarily pigs, considered superior model for human digestion
Key Limitation	Not proportional, ignores maintenance	Ignores digestibility, variable depending on intake	Score capping, uses inaccurate fecal digestibility	Requires more complex and precise data

Factors Influencing Protein Efficiency in Your Diet

Beyond the intrinsic quality measured by scores like DIAAS, how you consume protein affects its efficiency. Combining different protein sources can create a complete amino acid profile, especially beneficial in plant-based diets. Food processing can also impact protein structure and digestibility, either improving it by removing anti-nutritional factors or reducing it through damage from excessive heat.

Practical Importance of Protein Quality

For most individuals with diverse diets, obtaining sufficient high-quality protein isn't difficult. However, focusing on protein efficiency is particularly important for groups with higher needs or restricted diets, including infants, growing children, the elderly, and athletes. Protein quality metrics are also crucial for food labeling and nutritional guidance.

Conclusion: An Evolving Science of Protein Efficiency

The question "what is the efficiency of a protein called?" highlights the ongoing scientific effort to accurately measure protein quality. The evolution from early, less precise methods like PER and BV to the current standard, DIAAS, reflects a move toward more accurate, human-relevant assessments. DIAAS, with its focus on ileal digestibility and individual amino acid availability, provides the most reliable tool available today for evaluating how effectively the body can utilize dietary protein. Understanding these metrics helps ensure optimal nutrition for various populations.

For additional detail on the methodology and recommendations, consult the FAO report on protein quality evaluation in human nutrition.

Frequently Asked Questions

The main difference is the method of measuring digestibility. PDCAAS uses fecal digestibility, which can be inaccurate due to microbial interference in the large intestine. DIAAS uses ileal digestibility, measuring amino acid absorption at the end of the small intestine for a more precise score.

Yes, by combining complementary protein sources within a balanced diet, such as pairing grains and legumes, a complete and high-quality protein intake can be achieved.

PER was replaced because it was based on inaccurate assumptions derived from animal studies. Its main limitations were that it measured only growth (not maintenance needs) and used rats, whose amino acid requirements differ significantly from humans.

A DIAAS score over 100 indicates that a protein provides all indispensable amino acids in excess of human requirements based on the reference pattern. Unlike PDCAAS, DIAAS is not capped, allowing for better comparison of superior protein sources.

A limiting amino acid is the indispensable amino acid in a protein source that is present in the lowest proportion relative to human needs. It is important because the body can only build new protein up to the supply level of this most deficient amino acid.

The effect depends on the protein source and cooking method. For many plant-based proteins, cooking can improve digestibility by deactivating anti-nutritional factors. However, excessive heat can cause damage through chemical reactions, potentially lowering the bioavailability of certain amino acids.

Yes. Protein requirements and utilization patterns vary across different life stages. For example, DIAAS provides specific amino acid reference patterns for infants, young children, and adults to more accurately reflect their unique nutritional needs.

For most healthy adults consuming a varied diet, protein efficiency is less of a concern because the mix of protein sources will typically ensure a complete amino acid profile. However, it becomes more relevant for athletes, the elderly, or those with restricted diets.