Nitrogen is a chemical element and a building block for life. Although it makes up about 78% of the Earth’s atmosphere, humans cannot use it by breathing. Instead, we must obtain this element from food. The nitrogen from our diet is in a “fixed” or reactive form that our bodies can use for numerous processes.
The Function of Nitrogen in the Human Body
The primary way the body uses dietary nitrogen is through protein. Proteins are made from smaller units called amino acids, and nitrogen is a defining component of every amino acid. This structure allows proteins to perform many tasks. Without a steady supply of nitrogen from food, the synthesis of these compounds would halt, disrupting bodily operations.
Nitrogen-containing proteins build and repair tissues, including muscle, skin, and hair. They also form enzymes that facilitate metabolic reactions, from digesting food to converting nutrients into energy. Nitrogen is also a component of the nucleic acids DNA and RNA, which contain our genetic information and direct protein synthesis. The production of hormones and neurotransmitters, which regulate everything from growth to mood, also depends on nitrogen.
Common Foods Containing Nitrogen
Animal-Based Sources
Animal products are a significant source of dietary nitrogen because they provide high-quality, complete proteins. Red meats like beef and pork are dense in protein. Poultry, including chicken and turkey, offers a leaner source of this element. Fish, such as salmon and tuna, supply nitrogen and beneficial fatty acids.
Eggs are another excellent animal-based source with a high-quality protein profile. Dairy products, such as milk, cheese, and yogurt, also contribute nitrogen to the diet. These foods contain all the essential amino acids the body cannot produce on its own, making them efficient sources for meeting nitrogen requirements.
Plant-Based Sources
A variety of plant-based foods also offer nitrogen. Legumes, including beans, lentils, and chickpeas, are rich in protein. Soy products like tofu, tempeh, and edamame are notable for being complete proteins, which is less common in plant foods.
Nuts and seeds, such as almonds, peanuts, and sunflower seeds, are also good sources of nitrogen. Certain whole grains contain protein, and quinoa is a standout example because it provides all the essential amino acids. These plant-based options help individuals following vegetarian or vegan diets meet their nitrogen needs.
The Concept of Nitrogen Balance
Nitrogen balance compares the amount of nitrogen a person consumes with the amount they excrete, primarily in urine. This measurement reflects the body’s protein metabolism, indicating if the body is building, breaking down, or maintaining tissue. A healthy adult is typically in nitrogen equilibrium, where intake equals output. The balance can shift based on diet, age, and health status.
A positive nitrogen balance occurs when nitrogen intake is greater than nitrogen output. This indicates the body is retaining nitrogen to synthesize new tissues. This state is normal during periods of growth, such as childhood, pregnancy, or when building muscle mass through resistance exercise. It signifies that the body has sufficient resources to build and repair.
Conversely, a negative nitrogen balance happens when nitrogen loss exceeds intake. This means the body is breaking down more protein than it is getting from the diet, leading to a net loss of tissue. This condition can occur during serious illness, after major surgery, or during periods of starvation or inadequate protein consumption.