What term describes a state where nitrogen intake matches nitrogen expenditure?

The term that describes a state where nitrogen intake matches nitrogen expenditure is nitrogen equilibrium. This condition indicates that the amount of nitrogen consumed through dietary protein is equal to the amount being excreted, typically through urine and feces, as well as through other means such as sweat.

In this state, the body is neither in a deficit nor a surplus of nitrogen, which is important for maintaining overall health and supporting processes such as tissue repair and muscle maintenance. A nitrogen equilibrium is particularly relevant for individuals whose bodies are not in a significant state of growth or recovery, such as most adults who are not experiencing significant dietary changes, stress, or injuries.

The other options refer to different states of nitrogen balance: negative nitrogen balance occurs when nitrogen expenditure exceeds intake, indicating a potential loss of lean body mass, while positive nitrogen balance occurs when intake exceeds expenditure, often seen in states of growth, recovery from illness, or muscle building. Nitrogen deficiency, on the other hand, refers to an inadequate intake of nitrogen, leading to negative health outcomes. Thus, nitrogen equilibrium accurately captures the scenario described in the question.