nitrogen balance (N balance) The difference between the dietary intake of nitrogen (mainly protein) and its excretion (as urea and other waste products). Healthy adults excrete the same amount as is ingested, and so are in N equilibrium.

During growth and tissue repair (convalescence) the body is in positive N balance, i.e. intake is greater than loss and there is an increase in the total body pool of protein. In fevers, fasting, and wasting diseases the loss is greater than the intake and the individual is in negative balance; there is a net loss of protein from the body.

nitrogen balance n. the relationship between the nitrogen taken into the body and that excreted, denoting the balance between the manufacture and breakdown of the body mass. A negative nitrogen balance, when excretion exceeds intake, is usual after injury or operations as the energy requirements of the body are met disproportionately from endogenous sources.