What is the bioavailability score of a protein?

December 12, 2025 •

4 min read

According to the Food and Agriculture Organization (FAO), not all proteins are created equal in their ability to be absorbed and utilized by the body. A protein's nutritional quality is quantified by its bioavailability score, a measure of how efficiently the body can digest, absorb, and synthesize amino acids into new proteins.

Quick Summary

Protein bioavailability refers to how effectively the body can utilize a protein source, based on its amino acid profile and digestibility. Scores like DIAAS and PDCAAS help rank proteins, with animal sources generally having higher scores than plant-based ones, although strategic combining of plant proteins can improve their overall quality.

Key Points

Bioavailability Defined: Protein bioavailability measures how efficiently your body digests, absorbs, and utilizes a protein source to synthesize new proteins.
Amino Acid Profile is Key: A protein's bioavailability largely depends on its amino acid content, particularly the presence and balance of the nine essential amino acids.
DIAAS vs. PDCAAS: The Digestible Indispensable Amino Acid Score (DIAAS) is the most accurate modern metric, surpassing the older Protein Digestibility-Corrected Amino Acid Score (PDCAAS) by measuring ileal (small intestine) digestibility and providing uncapped scores.
Animal vs. Plant Protein: Animal proteins are generally higher in bioavailability due to a complete amino acid profile, while plant proteins can be strategically combined to achieve complete profiles.
Optimize Absorption: Enhance protein bioavailability by chewing food thoroughly, diversifying sources, and supporting gut health with fermented foods and probiotics.
Preparation Matters: Cooking methods impact protein quality; proper cooking can improve digestibility, while overcooking can diminish the availability of some amino acids.

What Exactly is Protein Bioavailability?

Protein bioavailability is a measure of how much of the protein you consume your body can actually absorb and put to good use. It's a critical concept in nutrition because simply consuming protein isn't enough; the body must be able to break it down into its constituent amino acids and effectively transport them to cells for tissue repair, muscle synthesis, and other vital functions. The factors that influence a protein's bioavailability include its amino acid composition, its structural density, and the presence of any anti-nutritional compounds that may inhibit digestion.

The Role of Essential Amino Acids

Protein bioavailability is significantly influenced by the amino acid profile of the protein source. There are 20 amino acids, nine of which are essential (EAAs) and must be obtained from the diet. Complete proteins contain all nine EAAs in sufficient amounts and generally have higher bioavailability. Incomplete proteins lack one or more EAAs, which can limit the body's ability to synthesize new proteins.

Factors Influencing Bioavailability Scores

Several factors contribute to a protein's bioavailability score:

Protein Source: Animal proteins typically have a more complete amino acid profile and higher digestibility compared to many plant proteins.
Anti-nutritional Factors: Compounds in some plant proteins can hinder digestion, although cooking can help mitigate these effects.
Processing and Cooking: Heating can impact the availability of certain amino acids, while proper cooking can improve digestibility.
Individual Digestive Health: An individual's digestive system efficiency plays a role in how well proteins are broken down and absorbed.

Key Metrics for Measuring Bioavailability Scores

Various methods have been developed to assess protein quality, with the most current being the Digestible Indispensable Amino Acid Score (DIAAS) and the older Protein Digestibility-Corrected Amino Acid Score (PDCAAS).

The Protein Digestibility-Corrected Amino Acid Score (PDCAAS)

Introduced in 1989, PDCAAS considers a protein's amino acid profile and its fecal digestibility. Scores are capped at 1.0, which limits the ability to differentiate between very high-quality proteins. Fecal digestibility measurements can also be less accurate as they don't account for bacterial activity in the colon.

The Digestible Indispensable Amino Acid Score (DIAAS)

Proposed in 2013, DIAAS is a more precise method that measures the digestibility of individual indispensable amino acids in the small intestine (ileum). DIAAS scores are not capped, allowing for a clearer ranking of high-quality proteins. It also uses different reference patterns for various age groups, increasing accuracy.

Comparison of Protein Quality Metrics

Understanding the different ways protein quality is assessed helps illustrate the advancements in nutritional science.


Metric	Basis of Evaluation	Key Advantage	Key Disadvantage
Biological Value (BV)	Measures nitrogen retained by the body from absorbed nitrogen.	Reflects absorbed protein utilization.	Doesn't account for digestibility and overestimates for incomplete proteins.
Net Protein Utilization (NPU)	Measures dietary protein retained by the body.	Considers both absorption and utilization.	Often uses animal models not directly applicable to humans.
Protein Efficiency Ratio (PER)	Measures weight gain in rats based on protein intake.	Simple laboratory method.	Not applicable to human needs and focuses only on growth.
Protein Digestibility-Corrected Amino Acid Score (PDCAAS)	Compares amino acid profile to a standard and corrects for fecal digestibility.	FDA-accepted and widely used.	Capped scores (max 1.0) and uses less accurate fecal data.
Digestible Indispensable Amino Acid Score (DIAAS)	Compares ileal digestibility of individual amino acids to a standard.	Most accurate modern method, uncapped for better comparison.	More complex and costly to implement.

Maximizing Your Protein Bioavailability

Applying knowledge of protein bioavailability to your diet is crucial for optimal nutrient intake.

Diversify Protein Sources

Consuming a variety of protein-rich foods helps ensure a complete intake of essential amino acids. Combining different plant-based proteins can create a complete amino acid profile, enhancing their overall bioavailability, which is particularly beneficial for those on vegetarian or vegan diets.

Optimize Food Preparation

Cooking methods can significantly impact protein bioavailability. Proper cooking of legumes can neutralize anti-nutritional factors, improving protein availability. However, excessive heat can sometimes degrade amino acids. Gentle cooking methods like steaming can help preserve protein quality.

Support Digestive Health

A healthy digestive system is essential for efficient protein absorption. Consuming fermented foods and probiotics can support gut health, which aids in nutrient absorption. Adequate stomach acid and thorough chewing also contribute to the initial breakdown of proteins.

Conclusion: The Modern Perspective on Protein Quality

The understanding of protein quality and bioavailability has advanced, with DIAAS now considered the most accurate metric. While older scores provided a foundation, DIAAS offers a more precise measure of how well a protein contributes to human nutritional needs by focusing on true absorption. For practical dietary choices, prioritizing diverse high-quality protein sources, optimizing food preparation, and maintaining digestive health are key strategies to maximize the benefits of the protein you consume. For those interested in delving deeper into the science of protein nutrition, authoritative resources such as those provided by the National Institutes of Health can offer further insights.

Frequently Asked Questions

The DIAAS is a modern and highly accurate method for evaluating protein quality. It measures the digestibility of individual essential amino acids at the end of the small intestine, reflecting the amount absorbed by the body. Unlike older methods, it does not cap scores, allowing for a better comparison of high-quality proteins.

Protein bioavailability is a component of overall protein quality. Protein quality considers both the amino acid profile and bioavailability (how well the protein is digested and absorbed), while bioavailability focuses specifically on the latter.

DIAAS is more accurate than PDCAAS because it measures amino acid digestibility at the ileum (end of the small intestine), providing a better representation of true absorption before bacterial fermentation occurs in the colon. PDCAAS relies on less precise fecal measurements.

No, it is a common misconception that complementary plant proteins must be consumed at the same meal. The body maintains an amino acid pool and can combine amino acids from different meals consumed throughout the day to form complete proteins.

High bioavailability protein sources generally include animal products such as milk, eggs, whey, casein, meat, and fish. Some plant sources like soy and quinoa also have high quality scores.

To improve protein absorption, chew your food thoroughly, consume a diverse diet of protein sources, maintain good gut health with probiotics, and use cooking methods that enhance digestibility without causing excessive amino acid degradation.

The PDCAAS system caps its scores at 1.0, so very high-quality proteins like whey and milk protein receive the same score. DIAAS is uncapped and uses more precise ileal digestibility measurements, allowing for better differentiation and ranking of top-tier proteins.