Nitrogen Balance = Nitrogen intake - Nitrogen loss
Sources of nitrogen intake include meat, dairy, eggs, nuts and legumes, and grains and cereals. Examples of nitrogen losses include urine, feces, sweat, hair, and skin.
Blood urea nitrogen can be used in estimating nitrogen balance, as can the urea concentration in urine.
Nitrogen Balance and Protein Metabolism
Positive nitrogen balance is associated with periods of growth, hypothyroidism, tissue repair, and pregnancy. This means that the intake of nitrogen into the body is greater than the loss of nitrogen from the body, so there is an increase in the total body pool of protein.
Negative nitrogen balance is associated with burns, serious tissue injuries, fevers, hyperthyroidism, wasting diseases, and during periods of fasting. This means that the amount of nitrogen excreted from the body is greater than the amount of nitrogen ingested. A negative nitrogen balance can be used as part of a clinical evaluation of malnutrition.
Nitrogen balance is the traditional method of determining dietary protein requirements. 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. In order 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 certain populations using the nitrogen balance technique (e.g. children).
- Protein (nutrient)
- Biological value
- Net protein utilization
- Protein efficiency ratio
- Protein digestibility
- Protein Digestibility Corrected Amino Acid Score
- "Definition: nitrogen balance from Online Medical Dictionary".
- World Health Organization Protein and amino acid requirements in human nutrition. WHO Technical Report Series 935 
- "VII. Monitoring Nutrition Therapy".
- 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.
- Elango R, Humayun MA, Ball RO, Pencharz PB (2011). Protein requirements of healthy, school-aged children determined by the indicator amino acid oxidation method. Am. J. Clin. Nutr. 94(6): 1545-1552.