How Do Humans Obtain the Nitrogen Necessary for Their Survival?

January 13, 2026 •

4 min read

Nitrogen is the fourth most abundant element in the human body, but despite making up about 78% of the atmosphere, we cannot use it directly from the air. In order to function, humans must obtain the nitrogen necessary for their survival through a process of assimilation from the food they eat.

Quick Summary

Humans acquire usable nitrogen by consuming plants or animals that have already assimilated nitrogen compounds from the environment. This dietary nitrogen is used to synthesize vital molecules like proteins and DNA. This intake is part of the larger nitrogen cycle, which begins with specialized bacteria in the soil.

Key Points

Dietary Intake is Key: Humans acquire usable nitrogen by consuming proteins found in plants and animals, as they cannot use atmospheric nitrogen gas.
Part of the Nitrogen Cycle: Human nitrogen acquisition is the final step of the nitrogen cycle, which begins with bacteria converting atmospheric nitrogen into usable compounds.
Essential for Protein Synthesis: Nitrogen is a core component of amino acids, which are the building blocks of all proteins necessary for tissue growth, repair, and function.
Critical for Genetic Material: It is an essential component of nucleic acids like DNA and RNA, which are critical for genetic information and cellular processes.
Dependent on Microorganisms: Our ability to get nitrogen depends on specialized bacteria that perform nitrogen fixation, converting inert nitrogen gas into a usable form for plants.
Crucial for Nitrogen Balance: Monitoring dietary protein intake helps maintain a healthy nitrogen balance, which is crucial for growth and preventing muscle wasting.

The Fundamental Role of Nitrogen in the Human Body

Nitrogen is a cornerstone of human life, playing a crucial role in building and maintaining the body's structure and function. It is a primary component of amino acids, the building blocks of proteins, which are essential for repairing tissues, growing muscles, and producing enzymes and hormones. Nitrogen is also integral to nucleic acids, namely DNA and RNA, which contain our genetic instructions and are vital for cell division and reproduction. Without a constant supply of usable nitrogen, these fundamental biological processes would cease.

The Journey of Nitrogen from Atmosphere to Plate

Since humans cannot fix atmospheric nitrogen gas ($N_2$), our access to this vital element depends entirely on other organisms. This process involves a complex series of steps known as the nitrogen cycle, which illustrates how nitrogen is converted into a bioavailable form and moves through the ecosystem.

Nitrogen Fixation: The First Crucial Step

The Problem with Atmospheric Nitrogen: The triple bond in $N_2$ gas makes it highly stable and inert, meaning most living things, including humans, cannot break it apart to use the nitrogen atoms.
The Role of Microbes: The cycle begins with nitrogen-fixing bacteria, such as Rhizobium, found in the root nodules of leguminous plants like peas, beans, and lentils. These microorganisms possess a unique enzyme called nitrogenase that converts atmospheric nitrogen ($N_2$) into ammonia ($NH_3$), a usable form of nitrogen.
Industrial Alternatives: Industrial processes, like the Haber-Bosch process, also convert atmospheric nitrogen into ammonia, which is then used to create nitrogen-rich fertilizers for crops.

Assimilation by Plants and Consumption by Humans

Plant Uptake: Plants absorb the usable nitrogen compounds, primarily nitrates and ammonium ions, from the soil through their root systems. They then incorporate this nitrogen into organic molecules, including amino acids and proteins.
Animal Intake: Herbivorous animals consume these nitrogen-rich plants, assimilating the nitrogen into their own body tissues. Carnivores, in turn, get their nitrogen by preying on these herbivores.
Human Dietary Intake: Humans obtain their nitrogen by consuming both plants and animals that have been part of this food chain. Dietary proteins are digested and broken down into amino acids, which are then used by the body for its own synthesis of proteins and other nitrogen-containing compounds.

Sources of Dietary Nitrogen

To ensure a consistent supply of nitrogen, humans must consume a diet rich in protein. A balanced diet should include a variety of both animal and plant-based protein sources.

Animal-Based Sources:

Lean meats (chicken, beef, pork)
Seafood (fish, shellfish)
Eggs
Dairy products (milk, yogurt, cheese)

Plant-Based Sources:

Legumes (beans, lentils, peas)
Nuts and seeds (almonds, peanuts, pumpkin seeds)
Soy products (tofu, edamame)
Whole grains (quinoa, oats)

The Consequences of Nitrogen Imbalance

Maintaining a proper nitrogen balance is crucial for good health. This balance is defined as the difference between the amount of nitrogen consumed and the amount excreted.

Comparison of Nitrogen Balance


State	Description	Consequences
Positive Nitrogen Balance	Nitrogen intake exceeds nitrogen excretion. Occurs during periods of growth, pregnancy, or tissue repair.	Supports tissue growth, muscle development, and healing. Essential for infants, bodybuilders, and recovering patients.
Negative Nitrogen Balance	Nitrogen excretion exceeds nitrogen intake. Occurs during illness, malnutrition, or starvation.	Results in muscle wasting, reduced immune function, and overall tissue breakdown. Can be a sign of poor nutritional status.
Nitrogen Equilibrium	Nitrogen intake equals nitrogen excretion. The normal state for healthy, non-growing adults.	Maintains healthy body functions without net gain or loss of protein.

Excess and Deficiency

While a deficiency in dietary protein can lead to a negative nitrogen balance, an excessive intake of protein can also put a strain on the body. Excess nitrogen is converted into urea in the liver and then excreted by the kidneys. High protein diets require the kidneys to work harder, and consistently high levels of nitrogen can stress these organs over time. Conversely, severe nitrogen deficiency, often seen in cases of malnutrition, can lead to severe health problems due to the breakdown of vital tissues.

Conclusion

In summary, humans acquire the nitrogen necessary for their survival exclusively through their diet, consuming organic nitrogen compounds found in proteins from plants and animals. We are incapable of processing the inert nitrogen gas that makes up the majority of our atmosphere. This reliance on the food chain is a testament to the intricate and delicate balance of the global nitrogen cycle, a process initiated by specialized microorganisms that convert atmospheric nitrogen into a form usable by living organisms. By understanding this fundamental biological pathway, we can better appreciate the importance of a balanced diet and the interconnectedness of all life on Earth. For additional information on the complex biochemical pathways involved, consult reputable scientific sources like the Encyclopedia Britannica's section on Nitrogen Fixation.

Frequently Asked Questions

No, humans cannot use the nitrogen gas ($N_2$) they breathe. The molecule is too stable and inert for our bodies to process it. We expel it unchanged with every breath.

The primary way humans get nitrogen is through their diet. We consume proteins from both plant-based and animal-based foods, which are then broken down into amino acids for the body to use.

Plants absorb nitrogen from the soil in the form of nitrates or ammonium, which are produced by nitrogen-fixing bacteria. Animals get their nitrogen by eating these plants or by eating other animals that have eaten plants.

Certain bacteria, like Rhizobium, are essential for converting inert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$), a usable form of nitrogen for plants. This process is called nitrogen fixation.

Nitrogen is critical for synthesizing essential molecules. It is a key component of amino acids (which form proteins), nucleic acids (DNA and RNA), and other vital compounds like hormones and enzymes.

Nitrogen is a single element, while nitrates are chemical compounds containing nitrogen and oxygen. The nitrogen we consume in protein is different from the nitrates found naturally in some vegetables.

A negative nitrogen balance means a person is excreting more nitrogen than they are consuming. This can lead to the breakdown of muscle and other body tissues and is a sign of poor nutrition or serious illness.