The difference between intake and excretion of nitrogen, which may be positive or negative.
When the intake of nitrogen (from protein) is equal to the excretion of nitrogen in the urine and feces, the individual is in nitrogen balance. Negative nitrogen balance is when excretion exceeds intake. Positive balance is when intake exceeds excretion. This happens in growth while the former happens in tissue wasting or when intake is of poor quality or quantity of protein.
Nitrogen balance is used as an indicator of protein status. Each amino acid possesses nitrogen; thus, protein is the only macronutrient that provides nitrogen within the diet. When a person is in nitrogen balance, their intake of nitrogen, which is nearly all from protein, is equal to their excretion of nitrogen, which is primarily from urea, but several other sources (such as sloughed skin cells, ammonia, uric acid, creatinine, etc.) as well. Positive nitrogen balance occurs when dietary intake of nitrogen exceeds excretion. For example, an athlete who is gaining lean body mass through resistance training will be in positive balance. Negative nitrogen balance occurs when the body losses exceed dietary intake. An athlete in negative balance is losing lean body mass.
The difference between the amount of nitrogen ingested and that excreted each day. If intake is greater, a positive balance exists; if less, there is a negative balance.
The quantification of the interplay between the ingestion of protein in one’s diet and the breakdown and elimination of protein from the body.