Biology:Nitrogen balance
In human physiology, nitrogen balance is the net difference between bodily nitrogen intake (ingestion) and loss (excretion):
[math]\displaystyle{ \mbox{nitrogen balance} = {\mbox{nitrogen intake}} - {\mbox{nitrogen loss}} }[/math]
Nitrogen balance is used as an index of protein metabolism. When more nitrogen is gained than is lost by a patient, they are considered to be "in positive nitrogen balance" and a state of overall protein anabolism. In contrast, a "negative nitrogen balance", in which more nitrogen is lost than is gained, indicates a state of overall protein catabolism.[1]
The body obtains nitrogen dietarily from protein, sources of which include meat, fish, eggs, dairy products, nuts, legumes, cereals, and grains. Nitrogen loss occurs largely through urine in the form of urea, as well as through feces, sweat, and hair and skin growth.
Blood urea nitrogen and urine urea nitrogen tests can be used to estimate nitrogen balance.
Nitrogen Balance and Protein Metabolism
Nitrogen is a fundamental component of amino acids, the molecular building blocks of protein. Therefore, measuring nitrogen intake and nitrogen loss can be used to study protein metabolism.[2]
Positive nitrogen balance is associated with periods of growth, hypothyroidism, tissue repair, and pregnancy. Because of this, the intake of nitrogen into the body is greater than the loss of nitrogen from the body. Thus, there is an increase in the total body pool of protein.
Negative nitrogen balance is associated with burns, serious tissue injuries, fever, hyperthyroidism, wasting diseases, and periods of fasting. This means that the amount of nitrogen excreted from the body is greater than the amount of nitrogen ingested.[3] A negative nitrogen balance can be used as part of a clinical evaluation of malnutrition.[4]
Nitrogen balance is the traditional method of measuring dietary protein requirements.[5] Determining dietary protein requirements using nitrogen balance requires that all nitrogen inputs and losses are carefully collected, to ensure that all nitrogen exchange is accounted for.[6] To control nitrogen inputs and losses, nitrogen balance studies usually require participants to eat very specific diets (so total nitrogen intake is known) and stay in the study location for the duration of the study (to collect all nitrogen losses). Because of these conditions, it can be difficult to study the dietary protein requirements of various populations using the nitrogen balance technique (e.g. children).[7]
Dietary nitrogen, acquired from metabolizing proteins and other nitrogen-containing compounds, has been linked to changes in genomic evolution. Species that primarily obtain energy from metabolizing nitrogen-rich compounds use more nitrogen in their DNA than species which primarily break down carbohydrates for their energy[citation needed]. Dietary nitrogen alters codon bias and genome composition in parasitic microorganisms.[8]
See also
- Protein (nutrient)
- Biological value
- Net protein utilization
- Protein efficiency ratio
- Protein digestibility
- Protein Digestibility Corrected Amino Acid Score
References
- ↑ Dickerson, Roland (April 2016). "Nitrogen Balance and Protein Requirements for Critically Ill Older Patients". Nutrients 8 (4): 226. doi:10.3390/nu8040226. PMID 27096868.
- ↑ World Health Organization Protein and amino acid requirements in human nutrition. WHO Technical Report Series 935 [1]
- ↑ "VII. Monitoring Nutrition Therapy". http://healthlinks.washington.edu/nutrition/section7.html.
- ↑ Barbosa-Silva MC (May 2008). "Subjective and objective nutritional assessment methods: what do they really assess?". Curr Opin Clin Nutr Metab Care 11 (3): 248–54. doi:10.1097/MCO.0b013e3282fba5d7. PMID 18403920.
- ↑ Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (Macronutrients). The National Academies Press: 2005
- ↑ Rand WM, Pellett PL, Young VR (2003). Meta-analysis of nitrogen balance studies for estimating protein requirements in health adults. Am.J.Nutr 77(1):109-127.
- ↑ "Protein requirements of healthy, school-aged children determined by the indicator amino acid oxidation method". Am. J. Clin. Nutr. 94 (6): 1545–1552. 2011. doi:10.3945/ajcn.111.012815. PMID 22049165.
- ↑ Seward EA and Kelly S (Nov 2016). "Dietary nitrogen alters codon bias and genome composition in parasitic microorganisms". Genome Biology 17 (226): 226. doi:10.1186/s13059-016-1087-9. PMID 27842572.
External links
- "Test Definition: NITF". https://www.mayocliniclabs.com/api/sitecore/TestCatalog/DownloadTestCatalog?testId=607704. (with clinical information & interpretation related to nitrogen balance and its clinical testing)
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