Net protein utilization
The net protein utilization, or NPU, is the percentage of ingested nitrogen that is retained in the body. It is used to determine the nutritional efficiency of protein in the diet,[1]: 11 that is, it is used as a measure of "protein quality" for human nutritional purposes.[2]
As a value, NPU can range from 0 to 1 (or 100), with a value of 1 (or 100) indicating 100% utilization of dietary nitrogen as protein and a value of 0 an indication that none of the nitrogen supplied was converted to protein.
Certain foodstuffs, such as eggs or milk, rate as 1 on an NPU chart.
Experimentally, this value can be determined by determining dietary protein intake and then measuring nitrogen excretion. One formula for NPU is:[citation needed]
- NPU = {0.16 × (24 hour protein intake in grams)} - {(24 hour urinary urea nitrogen) + 2} - {0.1 × (ideal body weight in kilograms)} / {0.16 × (24 hour protein intake in grams)}
NPU values can be either true or apparent, depending on whether the loss of endogenous nitrogen is taken into account or not; this is critical for precisely determining the efficiency of dietary protein utilization and the quality of different dietary protein sources.[1]: 12 The true NPU can be calculated as follows:[1]: 12
A closely related quantity, the biological value (BV), is the percentage of absorbed nitrogen that is retained in the body.[1]: 11 NPU and BV both measure nitrogen retention, however, the difference is that biological value is calculated from nitrogen absorbed, whereas net protein utilization is from nitrogen ingested.[3] BV is calculated as the product of NPU and digestibility.[1]: 11
Another closely related quantity is the net postprandial protein utilization (NPPU), which is the maximum potential NPU of a dietary protein source when determined in optimal, controlled conditions in healthy adults. To determine the NPPU of a dietary protein source, true dietary protein nitrogen retention is directly measured in the postprandial phase using 15N-labeled dietary proteins. This is done because the postprandial phase is critical for dietary protein utilization. The measurement of the immediate retention of dietary nitrogen following meal ingestion is a reliable way to assess protein nutritional efficiency.[1]: 12
The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a more modern rating for determining protein quality, and the current ranking standard used by the FDA.
The Digestible Indispensable Amino Acid Score (DIAAS) is a protein quality method, proposed in March 2013 by the Food and Agriculture Organization[4] to replace the current protein ranking standard, the Protein Digestibility Corrected Amino Acid Score (PDCAAS). The proposition is contested, however, due to lack of data.[5]
See also
References
- ^ a b c d e f "Scientific Opinion on Dietary Reference Values for protein: Dietary Reference Values for protein". EFSA Journal. 10 (2): 2557. February 2012. doi:10.2903/j.efsa.2012.2557.
- ^ Protein Quality–The 4 Most Important Metrics
- ^ Hoffman, JR; Falvo, MJ (September 2004). "Protein - Which is Best?". Journal of sports science & medicine. 3 (3): 118–30. PMID 24482589.
- ^ "FAO proposes new protein quality measurement - IFT.org". 2017-05-19. Archived from the original on 2017-05-19. Retrieved 2020-11-03.
- ^ "Potential impact of the digestible indispensable amino acid score as a measure of protein quality on dietary regulations and health". ResearchGate. Retrieved 2020-11-03.