Understanding the Biological Value Score
The biological value (BV) score is a traditional method for evaluating the quality of a dietary protein. It measures the proportion of absorbed protein from food that is incorporated into the body's proteins, indicating how efficiently the body uses a protein source for building and repairing tissues. This assessment considers the protein's amino acid profile, particularly the presence of sufficient essential amino acids (EAAs) that the body cannot produce. A lack of sufficient EAAs limits protein synthesis, resulting in a lower BV. Animal proteins generally have a higher BV than plant proteins due to their more complete amino acid composition.
How is the Biological Value Score Calculated?
The BV score is calculated by measuring nitrogen intake and excretion. The formula compares the nitrogen retained in the body to the nitrogen absorbed from the consumed protein:
- BV = (Nitrogen Retained / Nitrogen Absorbed) x 100
Nitrogen retention and absorption are typically derived from nitrogen intake and excretion in feces and urine. Some BV scores are relative to a reference protein, often the whole egg (score of 100). This can result in some proteins having relative BV scores over 100, though their 'true' BV remains below 100.
Comparing the Biological Value of Protein Sources
The BV score varies by protein source. Here's a comparison of typical BV scores:
| Protein Source | Biological Value (BV) | Notes |
|---|---|---|
| Whey Protein | 96–104 | A complete protein, often used as a supplement due to its high efficiency. |
| Whole Egg | 94–100 | Considered the gold standard reference protein, with an excellent amino acid profile. |
| Cow's Milk | 90–91 | A complete protein source, common in many diets. |
| Fish | 76–83 | High-quality animal protein source. |
| Beef | 74–80 | Another high-quality animal protein, but varies based on cut and preparation. |
| Soy Protein | 74–96 | A complete plant-based protein, though less bioavailable than animal proteins in some forms. |
| Quinoa | 83 | A plant-based source that contains all nine essential amino acids. |
| Rice | 74–83 | Contains a full profile of amino acids but is often low in one or more essential amino acids, particularly lysine. |
Limitations of Using the Biological Value Score
The BV score has limitations, leading to alternative protein scoring systems.
- Doesn't account for digestibility: BV only measures absorbed protein utilization, not total protein ingested or how easily it's digested.
- Affected by diet: BV can be influenced by an individual's overall diet and metabolism, as it's measured under controlled, non-real-world conditions.
- Measures maximal potential: BV shows the maximum potential quality at sub-requirement levels, which may not reflect quality at normal intake.
- Ignores protein combinations: BV of a mix of proteins can be higher than individual sources due to complementary amino acid profiles.
Alternative Protein Scoring Methods
To address BV's limitations, other methods provide a more accurate assessment of protein quality:
- Protein Digestibility-Corrected Amino Acid Score (PDCAAS): Compares a protein's amino acid profile to a reference and corrects for fecal digestibility. It may underestimate high-quality proteins.
- Digestible Indispensable Amino Acid Score (DIAAS): The current standard recommended by the FAO. It measures digestibility of individual indispensable amino acids in the small intestine for a more accurate absorption figure than PDCAAS.
How the Biological Value Score is Still Relevant
Despite newer methods, the BV score remains relevant. It provides a foundational understanding of protein quality, highlighting the importance of a complete amino acid profile. It can also guide dietary choices for combining proteins; for instance, combining low-BV plant proteins like rice and beans can create a meal with a high overall BV.
For most people with balanced diets, focusing on maximizing BV in every meal isn't necessary, as the body's amino acid pool is recycled. However, athletes or those with specific goals might use high-BV sources strategically for muscle support.
Conclusion
The biological value score measures how efficiently the body uses absorbed protein for tissue synthesis, based on its essential amino acid profile. While limited, especially in not accounting for digestibility, leading to newer measures like DIAAS, understanding BV is valuable. Consuming a variety of protein sources, including both animal and plant proteins, is key to ensuring a high overall biological value in your diet and meeting nutritional needs.
For more information on protein quality, you can consult the official publications of the Food and Agriculture Organization (FAO).
