Nitrogen is abundant in the atmosphere, but animals, including humans, do not have the ability to use atmospheric nitrogen directly. Instead, in a process called nitrogen fixation, bacteria known as rhizobia convert nitrogen from the atmosphere into a usable form for plants, according to the University of Hawaii's College of Tropical Agriculture and Human Resources. Plants then supply animals with the nitrogen necessary for life and health.
Function
Nitrogen is a component of amino acids, the building blocks of proteins. When you eat protein, your body breaks it down into its constituent amino acids, then uses the collection of amino acids to rebuild new proteins you need for growth, immune function, tissue repair, and manufacture of enzymes and hormones, says the University of Illinois McKinley Health Center. Nitrogen also plays a role in your genetics, as a part of molecules called nucleic acids. Examples of nucleic acids are the RNA and DNA on the chromosomes in your cells.
Dietary Sources
Because your body manufactures and degrades proteins relatively quickly, you do not store nitrogen the way you store carbohydrates and fats. Therefore, you need to consume high-quality protein on a daily basis to meet your nitrogen needs. High-quality proteins contain all the essential amino acids, the ones you must include in your diet because your body cannot manufacture them. Animal sources of proteins, including fish, meat, eggs and dairy products, all are high-quality proteins. Most plant sources of proteins do not contain all the amino acids you need, but you can combine them in your diet so they complement each other and provide all your essential amino acids.
Metabolism
Proteins from your diet enter your digestive tract, where they are broken down into individual amino acids. Once they are transported into your cells, the amino acids may undergo a process called transamination, in which the nitrogen-containing portion of the amino acid is transferred to a glutamate molecule, explains Dr. Michael King of the Medical Biochemistry Page. The glutamate molecule then transfers the nitrogen to form a new amino acid that your body is able to manufacture. The glutamate molecule may also transfer nitrogen in the form of ammonia, a nitrogen-containing compound excreted by bacteria in your intestinal tract. In this way, glutamate serves as a nitrogen shuttle, depending on your body's nitrogen needs.
Excess Nitrogen
You are in nitrogen balance when your daily nitrogen intake and excretion are approximately the same. If you take in more nitrogen than you use, your body is unable to store it and will eliminate the excess. This state of negative nitrogen balance requires your liver and kidneys to convert surplus nitrogen to ammonia, primarily in the form of urea, as it is excreted in your urine.
Nitrogen Deficiency
Lack of any one essential amino acid leads to a nutritional imbalance, says King of the Medical Biochemistry Page, because the low level of the so-called limiting amino acid prevents your body from synthesizing the proteins you need. This inability to manufacture proteins due to insufficient quantities of one or more essential amino acids leads to a disorder called kwashiorkor. Uncommon in developed countries, kwashiorkor frequently afflicts growing children in poor countries of the world that have limited sources of high-quality proteins.
References
- University of Hawaii College of Tropical Agriculture and Human Resources: Nitrogen and Tropical Agriculture
- University of Illinois McKinley Health Center: Macronutrients--the Importance of Carbohydrate, Protein and Fat
- Michigan State University Department of Chemistry: Nucleic Acids
- Medical Biochemistry Page: Nitrogen Metabolism
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