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The term "nitrogen balance" refers to the amount of nitrogen the body excretes, as opposed to the amount of nitrogen the body takes in. All of the macronutrients — protein, carbohydrate, and fat — are made up of carbon, hydrogen, and oxygen molecules. Protein alone also contains an additional nitrogen molecule. When the body digests protein, these nitrogen molecules are generally released into the blood. Measuring bodily nitrogen levels can be the most accurate way to determine whether the body is receiving adequate, inadequate, or excess protein.
There are three states of nitrogen balance: negative, positive. and equilibrium. If an individual has a negative nitrogen balance, that person's nitrogen output is greater than his nitrogen input. Because protein is the only macronutrient containing a nitrogen molecule, a negative balance can be a sign of inadequate protein consumption and malnutrition.
If an individual has a positive nitrogen balance, it means that person is consuming more protein than his body needs. This is an ideal state for athletes and body builders, because the extra protein will most likely contribute to muscle growth. Excess protein can also help athletes and body builders recover faster from workouts.
If an individual's nitrogen balance has reached a state of equilibrium, it means that person is excreting about the same amount of nitrogen as he are taking in. This is generally a normal state of affairs for healthy adults eating a balanced diet. Most people don't usually need to consume the high levels of protein that body builders and athletes often need to grow strong muscles.
Nitrogen is usually excreted through the urine, so nitrogen levels in the body are often measured using a urea nitrogen test of urine. The results of the test are then typically compared to the nitrogen content of the individual's diet. The person will generally be said to have a positive, negative, or equal nitrogen balance, depending on the difference between his urea nitrogen levels and the nitrogen content of his diet.
The human body usually needs more than just protein to maintain appropriate nitrogen levels. Dietary protein should be of high quality, such as that typically found in eggs and lean meats. The human body also generally needs an adequate supply of fats and carbohydrates. These macronutrients are widely considered essential to energy production. When dietary levels of fat and carbohydrate fall too low, the body uses protein for energy, which may deplete the body's nitrogen levels and inhibit the body's ability to renew damaged cells.