Four Methods for Assessing Protein Quality
Sophia Williams
2026-03-22
3 min. read
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The answer is simple: it depends on which of these products is the best source of protein? eggs, beef, cottage cheese or soybeans? It depends on whether you're looking for the protein that's most absorbable, or perhaps the one that most accurately reflects the structure of amino acids in the human body. Or do you want the amino acid profile to be balanced and there's no obvious lack of any amino acid? There are many possibilities, as many as there are methods for evaluating the quality of protein products. In this article, you will find out what the most popular methods for evaluating protein quality are, how to apply them, and how the selected products rank in them.
Protein growth efficiency ratio (PER)
The protein growth efficiency ratio (PER) signifies the proportion of body weight increase in grams upon consumption of a certain type of protein. This method of evaluating protein quality is employed by baby food manufacturers. To compute this ratio, young animals, predominantly rats, are fed a diet where 10% of the energy originates from a studied protein source. Body weight is tracked over a period and subsequently compared to the amount of protein consumed. Aside from infants, this indicator does not have substantial application in human nutrition. PER = Body weight increase (grams) / quantity of protein from the studied product (grams).
The biological value of protein (BV)
Biological value (BV) is one of the most frequently utilized methods for assessing protein quality. It shows how much protein, specifically nitrogen, that is absorbed into the bloodstream persists in the body, for example, reaching the muscles permanently. It measures and compares the amount of nitrogen that is absorbed and the quantity of nitrogen that is retained in the body. This factor is primarily calculated in animals, although it is occasionally determined in humans as well. This is achieved by feeding the test subjects a protein-deficient diet for 7-10 days, followed by the introduction of the protein sources under examination into the diet and the verification of the amount of excreted nitrogen. BV = retained nitrogen / absorbed nitrogen x 100.
Net protein utilization (NPU) application
Net protein utilization (NPU) is very similar to the previously mentioned indicator. While BV compares the amount of retained nitrogen to the absorbed nitrogen, NPU compares the ratio of retained nitrogen to the total amount of consumed protein. In a way, it is more practical because BV can rate the chosen product highly only because a small amount of the protein is absorbed from it. NPU evaluates what proportion of protein remains from what we have consumed. NPU = retained nitrogen / consumed nitrogen × 100.
Updated protein amino acid appetite scale (PDCAAS)
The most up-to-date and currently most frequently used method of assessing protein quality is to compare the maximum possible amount of limiting amino acid in a protein under study against the amount in the same amino acid of the reference protein, which is mainly egg or milk. The resulting value is then multiplied by the absorbability of the protein under test. Although this is probably the best method to assess protein quality, it has its drawbacks. The first is the fact that the highest possible amino acid content is 1.0. No source can achieve the exact amount of amino acid, regardless of its actual quality. Amino values that exceed 1.0 are found in the reference product PDCAAS gmg, therefore, this actually occurs over and over. For some protein compounds, there is no known limiting protein content. The correctness of the PDCAAS index depends on the assumption that the selected reference protein actually has an optimal composition for the human body, which is actually not certain.