What is Biological value?

What is Biological value?

Biological value is a way of ranking dietary proteins by how efficiently your body turns the protein you absorb into your own body protein. It answers a narrow but useful question: of the protein nitrogen that actually crosses your gut wall, what fraction do you keep and build with, and what fraction do you burn for energy and pee out as urea?

A protein rated 100 would, in theory, be retained completely; a protein rated 60 means roughly 40 percent of the absorbed nitrogen is lost. BV is one of the oldest protein-quality scores, developed by Karl Thomas and Thomas Osborne in the early 1900s and refined by Mitchell in 1924. It sits alongside newer metrics like PDCAAS and DIAAS, and older ones like protein efficiency ratio (PER) and net protein utilization (NPU).

What sets BV apart is that it measures retention directly through a nitrogen-balance study rather than estimating quality from amino acid content on paper. Because whole egg is retained so completely, it was chosen as the reference protein and pinned at 100, which is why you often see egg, whey, and milk cited as the gold-standard proteins in supplement marketing.

The score reflects two things at once: how closely a protein's amino acid profile matches human needs, and, in part, how well its limiting amino acid is supplied. A protein short in one essential amino acid, like the lysine shortfall in wheat, retains poorly and scores low, because the missing amino acid caps how much of the rest can be used.

How it works

Biological value is calculated from a nitrogen-balance study, because protein is about 16 percent nitrogen and nitrogen is the element the body tracks. A subject is first fed a protein-free diet so researchers can measure obligatory nitrogen losses, the nitrogen you excrete in urine and feces even when eating no protein at all. The subject then eats a fixed amount of the test protein as the only nitrogen source, and all nitrogen taken in, plus all nitrogen lost in urine and feces, is collected and measured.

True BV is the nitrogen retained divided by the nitrogen absorbed, expressed as a percentage: BV = ((Ni − Fecal N − Urinary N) ÷ (Ni − Fecal N)) × 100, where the denominator subtracts fecal losses to represent absorbed nitrogen. Retained nitrogen is a proxy for protein your body kept and used to build muscle, enzymes, antibodies, hormones, and repair tissue.

The score is driven mostly by the protein's essential amino acid profile relative to human requirements. When every essential amino acid is present in the right ratio, the liver can assemble new proteins with little waste, so retention is high. When one amino acid runs short, that limiting amino acid sets the ceiling: the surplus of the others cannot be used for synthesis, so it is deaminated, the nitrogen is stripped off and excreted as urea, and the carbon skeleton is burned or stored.

This is why animal proteins, whose profiles closely match ours, score high, while single plant proteins, often short in lysine or methionine, score lower. A critical caveat is that BV is measured at protein intakes below maintenance, where the body clings to every gram; measured near normal intakes the scores fall, so BV tends to flatter proteins under test conditions you would not eat in daily life.

The formula

BV = ((Ni − Fecal N − Urinary N) ÷ (Ni − Fecal N)) × 100

Ni = nitrogen intake. The denominator (intake minus fecal loss) is nitrogen ABSORBED; the numerator is nitrogen RETAINED. Relative BV pins whole egg at 100 and expresses other proteins against it, which is why whey can score above 100.

How to apply it

• Read it as retention, not digestibility: BV tells you how much absorbed nitrogen you keep, not how much you absorb in the first place. A protein can be poorly digested yet still post a high BV for the fraction that gets absorbed, which is why BV is paired with a digestibility figure in fuller scores like PDCAAS.
• Use it to rank single protein sources: BV is most useful for comparing one isolated protein against another: whey versus casein, egg versus beef, soy versus wheat. Whey (~104) and egg (100) top the list, milk and beef sit mid-to-high, and single plant proteins trail because of a limiting amino acid.
• Combine proteins to beat any single score: Mixing complementary proteins raises the effective value of a meal above either source alone. Rice is low in lysine and beans are low in methionine, but eaten together their amino acids fill each other's gaps, giving a blend that rivals animal protein for retention.
• Prioritize the limiting amino acid: A protein's BV is capped by its scarcest essential amino acid. For most grains that is lysine; for legumes it is methionine. Adding a small amount of the limiting amino acid, or a food rich in it, lifts retention far more than simply eating more of the same protein.
• Weigh total daily protein over any one score: BV differences shrink once you hit an adequate protein intake, because surplus amino acids from a lower-BV food still add up across the day. For most lifters, eating 1.6 to 2.2 g of protein per kg of bodyweight matters more than chasing the single highest-BV source.
• Treat BV as historical, not regulatory: The FAO, WHO, and FDA no longer recommend BV for judging protein quality; PDCAAS is the labeling standard and DIAAS is the current research method. Use BV to understand old data and marketing claims, but rely on PDCAAS or DIAAS for a modern, human-relevant comparison.

Types

Worked example

Say a nitrogen-balance study feeds a subject a fixed amount of a test protein and collects every gram of nitrogen going in and coming out. Here is how the same absorbed protein produces very different BV scores depending on how much nitrogen the body retains versus excretes. Numbers are illustrative but follow the real formula.

Every protein here was absorbed equally, yet egg and whey retain roughly 30 percent more nitrogen than wheat. The gap is the limiting amino acid: wheat is short in lysine, so the excess of its other amino acids is deaminated and lost as urea rather than built into tissue.

Biological value vs PDCAAS vs DIAAS

BV came first and measures retention directly but ignores how much protein you actually digest. PDCAAS added a digestibility correction and became the label standard. DIAAS refined that by measuring each amino acid's absorption at the end of the small intestine, and is now the method experts prefer.

By goal

• Muscle building: Favor high-BV, leucine-rich proteins like whey, egg, and milk around training, because they supply the full essential amino acid profile that drives muscle protein synthesis. That said, total daily protein of about 1.6 to 2.2 g per kg matters more than the BV of any single serving.
• Plant-based eaters: No single plant protein matches egg or whey, but combining sources fixes that. Pair grains with legumes across the day so lysine and methionine fill each other's gaps, and lean on higher-quality plant proteins like soy, which posts a BV and DIAAS well above most other plants.
• General health and older adults: Higher-quality proteins help you meet needs with less total food, which matters when appetite is low. Spreading 20 to 40 g of a high-BV protein across meals supports muscle maintenance and offsets the blunted anabolic response that comes with age.

Common misconceptions

• "A higher biological value means a protein is better for building muscle." BV ranks retention efficiency, not muscle growth. Once you eat enough total protein, differences between a BV of 80 and 100 largely disappear, because surplus amino acids from a lower-BV food still accumulate across the day. Total intake and leucine content predict muscle gain better than BV alone.
• "Biological value measures how well you digest a protein." BV measures only what happens to nitrogen after it is absorbed, not how much is absorbed. A protein can digest poorly yet still score high on BV. This blind spot is exactly why PDCAAS and DIAAS were created, since both fold digestibility into the final quality score.
• "A protein cannot score above 100." On the relative scale, whey concentrate scores about 104. Egg was pinned at 100 as the reference, so any protein retained slightly more efficiently than egg reads above 100. It does not mean more than all the protein was retained, only that it beat the benchmark.
• "Plant proteins are useless because their biological value is low." Single plant proteins score lower because each is short in one amino acid, but combining complementary sources or eating varied protein across the day closes the gap. Soy already scores high on its own, and total daily amino acid intake, not one food's BV, is what counts.
• "Biological value is the standard used on nutrition labels." It is not. The FDA and FAO replaced BV decades ago; PDCAAS is the required standard for protein claims on US and Canadian labels, and DIAAS is the newer research method. BV survives mostly in supplement marketing and older textbooks, not in current regulation.

Related terms

Biological value FAQ

What is biological value in simple terms?

Biological value is a score for how efficiently your body turns a protein you absorb into your own body protein. Of the protein nitrogen that crosses your gut wall, BV is the percentage you keep and build with rather than burn for energy and excrete as urea.

Which protein has the highest biological value?

Whey protein has the highest biological value, around 104 on the scale where whole egg is set at 100. Egg follows at 100, then cow milk near 91 and beef around 80. Whey can exceed egg because processing concentrates its essential amino acids.

Why is egg protein set at 100?

Whole egg was chosen as the reference protein because its amino acid profile so closely matches human needs that the body retains almost all the absorbed nitrogen. Researchers pinned egg at 100 and rank every other protein against it, which is why some proteins score above 100.

How is biological value calculated?

Biological value comes from a nitrogen-balance study. Researchers measure nitrogen eaten and nitrogen lost in urine and feces, then divide the nitrogen retained by the nitrogen absorbed and multiply by 100. Since protein is about 16 percent nitrogen, tracking nitrogen tracks protein use.

What is the difference between biological value and PDCAAS?

Biological value measures only nitrogen retention after absorption and ignores how much protein you digest. PDCAAS multiplies an amino acid score by digestibility and caps the result at 1.0, so it reflects both quality and digestibility. PDCAAS is the current labeling standard; BV is historical.

Is biological value the same as DIAAS?

No. DIAAS is a newer, more precise metric that measures how much of each individual essential amino acid is absorbed at the end of the small intestine. Biological value only tracks total nitrogen retention. DIAAS is uncapped and is the method experts now prefer over BV or PDCAAS.

Does a high biological value mean more muscle growth?

Not directly. BV ranks retention efficiency, not muscle gain. Once you eat enough total protein, the difference between a moderate and a high BV mostly disappears. Total daily protein and leucine content predict muscle growth far better than the biological value of any single food.

Do plant proteins have a low biological value?

Most single plant proteins score lower because each is short in one essential amino acid, usually lysine in grains or methionine in legumes. But soy scores high on its own, and combining complementary plant proteins across the day raises the effective value close to animal protein.

Can a protein have a biological value over 100?

Yes, on the relative scale. Whey concentrate scores about 104 because whole egg was set at 100 as the benchmark. A score above 100 simply means the protein is retained slightly more efficiently than egg, not that more than all of it was somehow kept.

Why is biological value not used on nutrition labels anymore?

Biological value ignores digestibility and is measured at protein intakes below maintenance, which flatters proteins under conditions you would not eat daily. The FAO and FDA replaced it with PDCAAS for labeling and DIAAS for research, both of which build digestibility into the score.

References

1. Biological value. Wikipedia
2. The Use of Biological Value of a Protein in Evaluating Its Quality for Human Requirements. FAO, Food and Agriculture Organization of the United Nations
3. Wolfe RR, et al. Protein Quality in Perspective: A Review of Protein Quality Metrics and Their Applications. Nutrients, 2022. PMC8912699
4. Moughan PJ, et al. Digestible Indispensable Amino Acid Score (DIAAS): 10 Years On. Frontiers in Nutrition, 2024. PMC11252030
5. Marinangeli CPF, House JD. Protein Quality as Determined by the Digestible Indispensable Amino Acid Score: Evaluation of Factors Underlying the Calculation. Nutrition Reviews, 2017. PMC6322793
6. Protein quality. Wikipedia