Food Chemistry and Fish in Nutrition

8.1.5.Nitrogen balance

Nitrogen balance

 

Since protein is the main source of nitrogen in body the dietary protein must make up nitrogen lost from body to maintain nitrogen balance. Nitrogen balance is the difference in the amount of nitrogen consumed and the amount of nitrogen excreted in the urine, sweat and feces. If an individual’s total nitrogen content of the urine and feces equals the amount of dietary nitrogen then the individual is said to be in nitrogen balance or equilibrium

          Fecal nitrogen (N) + Urinary nitrogen (N) = Dietary nitrogen (N)

          N output = N intake

Healthy adults are normally in zero nitrogen balance

 

Positive nitrogen balance

If the ratio of N intake to N output is greater than one then it is called as positive nitrogen balance or if the N output is less than N intake then the individual is in positive nitrogen balance. In the positive nitrogen balance most of dietary nitrogen is retained in the body and  less is eliminated from body. More over in positive nitrogen balance the tissue protein content increases due to increased protein synthesis. Usually it occurs during growth, pregnancy, lactation and post operative recovery.

 

Negative nitrogen balance

If the nitrogen output is more than the N intake then the individual is in negative nitrogen balance or if the ratio of N intake to N output is less than one then the individual is in negative nitrogen balance. In the negative nitrogen balance nitrogen lost is not replaced by dietary nitrogen. It occurs in malnutrition and other wasting diseases where there is tissue breakdown like starvation, uncontrolled diabetes mellitus and cancer. Menstruating women may have transient negative nitrogen balance if proper replacement for nitrogen lost is not possible. Severe physical exercise may alsolead to transient negative nitrogen balance because of atrophy of muscle. The nitrogen balance of the body depends on the following factors such as the physiological state of the individual, adequacy of energy intake from carbohydrates and fats and the capacity to adjust to levels of intake.