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Biological Value (BV)
**Biological Value (BV)** is a measure of protein quality that expresses the proportion of absorbed protein nitrogen retained by the body for growth and maintenance, rather than excreted. A higher BV indicates that more of the nitrogen reaching the bloodstream is actually used to build and repair tissue.
How Biological Value Is Measured
BV is determined experimentally through nitrogen-balance studies. Researchers measure how much nitrogen a subject consumes, then subtract the nitrogen lost in feces (to find the absorbed amount) and the nitrogen lost in urine (to find what was not retained). The retained fraction, divided by the absorbed fraction, yields the value. Nitrogen-balance methods are the same foundational technique used to establish protein intake recommendations: a negative balance indicates a catabolic state, while a positive balance indicates an anabolic one.
Because BV reflects only what happens after absorption, it is often paired with digestibility to give a fuller picture. Net Protein Utilization (NPU) is the product of Biological Value and digestibility, combining how much protein is absorbed with how efficiently the absorbed portion is retained.
Limitations and the Shift to PDCAAS and DIAAS
BV is one of the oldest protein-quality metrics, and its age shows. It is sensitive to the experimental conditions under which it is measured — energy intake, protein dose, and whether the subject is in a growth phase can all shift the result, making cross-study comparison difficult. BV also says nothing directly about a protein’s amino acid composition, so two proteins with very different limiting amino acids can post similar values.
For these reasons, regulatory and scientific bodies largely moved to amino-acid-based scores. PDCAAS compares a protein’s amino acid profile against requirements and corrects for digestibility, but it truncates its top scores to a maximum of 1.00, so several high-quality proteins appear identical even when their real-world effects differ. DIAAS, the more recent standard, measures the digestibility of individual indispensable amino acids and, per FAO guidance, does not truncate values above 100%. For readers weighing these metrics when choosing a product, our guide to choosing a protein powder walks through how the scores translate into practical decisions.
Relevance to Potato Protein
Plant proteins are generally reported to have lower protein-quality scores than animal proteins, but potato protein is an exception worth noting. The Digestible Indispensable Amino Acid Score (DIAAS) for potato protein isolates has been reported as high as 100 (Food Science & Nutrition, Herreman et al., 2020, PMID:33133540), placing it among the highest-scoring plant sources by the current standard. Where older BV figures exist for various foods, the modern amino-acid-based scores give a more directly comparable account of how well a protein meets human requirements.
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