[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Nitrogen balance [Biochemistry](https://durgical.com/en/biochemistry/) · Topic # Nitrogen balance Nitrogen balance compares the nitrogen eaten (as protein) with the nitrogen lost, mostly as urea. It shows whether the body is building or losing protein. Updated 2026-11-01 ## Key facts - Nitrogen balance = nitrogen intake − nitrogen losses (urine, faeces, skin); protein is about 16 % nitrogen, so g of nitrogen = g of protein ÷ 6.25. - Positive balance (intake > losses): growth, pregnancy, recovery from illness, muscle building, and after insulin or anabolic hormones. - Negative balance (losses > intake): starvation, a diet lacking an essential amino acid, fever, sepsis, trauma, burns, surgery, uncontrolled diabetes, cortisol excess and immobilisation. - A healthy adult with adequate intake is in nitrogen equilibrium (balance ≈ 0). - Urinary urea nitrogen is about 80–90 % of urinary nitrogen and is used to estimate losses; about 4 g/day is added for losses not measured (other nitrogen compounds, stool, skin). ## In detail - 1. The body has no protein store: every day about 300 g of protein are broken down and rebuilt (protein turnover), and the nitrogen not reused is excreted. - 2. Amino acid nitrogen goes to glutamate by transamination, is released as ammonia, and the liver converts it to urea. - 3. Clinical calculation: N balance = (protein intake in g ÷ 6.25) − (24-h urinary urea nitrogen in g + about 4 g). - 4. In catabolic states, cortisol, glucagon, catecholamines and cytokines break down muscle protein to supply amino acids for gluconeogenesis, acute-phase proteins and repair. - 5. If even one essential amino acid is missing, the others cannot be used for synthesis and are deaminated, so the balance turns negative even with enough total protein. - 6. Minimum obligatory nitrogen loss on a protein-free diet is the baseline needed to set the safe protein intake. **Also called** Positive and negative nitrogen balance, Protein turnover ## Clinical notes - In intensive care, a negative balance in sepsis or burns signals muscle wasting; nutrition aims to reduce it, although it rarely reaches zero in the acute phase. - In chronic kidney disease, urea retention limits protein intake, but too little protein leads to malnutrition. - In kwashiorkor and marasmus the balance is negative; on recovery it becomes strongly positive. ## Pathways - [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/) ## Related conditions - [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/) - [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/) - [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/) - [Refeeding syndrome](https://durgical.com/en/conditions/refeeding-syndrome/) - [Kwashiorkor](https://durgical.com/en/conditions/kwashiorkor/) - [Marasmus](https://durgical.com/en/conditions/marasmus/) ## Related - [Protein quality and essential amino acids](https://durgical.com/en/biochemistry/topics/protein-quality-and-essential-amino-acids/) - [Urea](https://durgical.com/en/biochemistry/molecules/urea/) - [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/) - [Transamination and deamination](https://durgical.com/en/biochemistry/topics/transamination-and-deamination/) - [Energy requirements and basal metabolic rate (BMR)](https://durgical.com/en/biochemistry/topics/energy-requirements-and-basal-metabolic-rate/) - [Glutamine](https://durgical.com/en/biochemistry/molecules/glutamine/) - [Fed, fasting and starvation states](https://durgical.com/en/biochemistry/topics/fed-fasting-and-starvation-states/) ## Test yourself Think of the answer, then tap the question to see it. ## How is the nitrogen content of dietary protein estimated? Dividing grams of protein by 6.25, because protein is about 16 % nitrogen. ## Which two situations give a positive nitrogen balance? Growth in childhood and pregnancy (also recovery from illness and muscle building), when more protein is built than broken down. ## Why does a diet missing one essential amino acid cause negative nitrogen balance? Protein synthesis stops, so the other amino acids are not used, are deaminated and their nitrogen is excreted as urea. ## Which urinary compound is used to estimate nitrogen losses? Urea (24-hour urinary urea nitrogen), which makes up most of urinary nitrogen; about 4 g/day is added for other losses. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/nitrogen-balance/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Protein in diet: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/002467.htm) (MedlinePlus, US National Library of Medicine, 2026); [Plasma amino acids: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003361.htm) (MedlinePlus, US National Library of Medicine, 2026); [Human energy requirements](https://www.fao.org/4/y5686e/y5686e00.htm) (Food and Agriculture Organization of the United Nations (FAO/WHO/UNU expert consultation), 2004); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). [← All of biochemistry](https://durgical.com/en/biochemistry/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. 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