The net protein utilization, or NPU, is the ratio of amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 converted to protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s to the ratio of amino acids supplied. This figure is somewhat affected by the salvage of essential amino acid

Essential amino acid

An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...

s within the body, but is profoundly affected by the level of limiting amino acids

Essential amino acid

An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...

 within a foodstuff.

Experimentally, this value can be determined by determining diet

Diet (nutrition)

In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...

ary protein intake and then measuring nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 excretion

Excretion

Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...

. One formula for NPU is:

NPU = ((0.16 × (24 hour protein intake in grams)) - ((24 hour urinary urea

Urea

Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

 nitrogen) + 2) - (0.1 × (ideal body weight in kilograms))) / (0.16 × (24 hour protein intake in grams))

As a value, NPU can range from 1 to 0, with a value of 1 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 egg

Egg (food)

Eggs are laid by females of many different species, including birds, reptiles, amphibians, and fish, and have probably been eaten by mankind for millennia. Bird and reptile eggs consist of a protective eggshell, albumen , and vitellus , contained within various thin membranes...

s or milk

Milk

Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

, rate as 1 on an NPU chart.

The Protein Digestibility Corrected Amino Acid Score

PDCAAS

Protein Digestibility Corrected Amino Acid Score is a method of evaluating the protein quality based on both the amino acid requirements of humans and their ability to digest it...

 is a more modern rating for determining protein quality.

See also

• Biological value
  Biological Value
  Biological value is a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism's body. It summarises how readily the broken down protein can be used in protein synthesis in the cells of the organism. Proteins are the major source of...
  
  
• Protein efficiency ratio
  Protein efficiency ratio
  Protein efficiency ratio is based on the weight gain of a test subject divided by its intake of a particular food protein during the test period....
  
  
• Nitrogen balance
  Nitrogen balance
  Nitrogen balance is the measure of nitrogen output subtracted from nitrogen input.Blood urea nitrogen can be used in estimating nitrogen balance, as can the urea concentration in urine....
  
  
• Protein digestibility
• Protein Digestibility Corrected Amino Acid Score