Nitrogen is a fundamental chemical component of amino acids, the molecular building blocks of protein.
[2] The body obtains nitrogen from dietary 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 faeces, sweat, and growth of hair and skin.
Negative nitrogen balance is associated with burns, serious tissue injuries, fever, hyperthyroidism, wasting diseases, and periods of fasting.
Physical exercise is also known to influence nitrogen excretion, adding another variable that requires control during these studies.