What Is Protein Homeostasis?

Nitrogen balance refers to the equilibrium state between nitrogen intake and discharge. It reflects the relationship between the body's intake of nitrogen and its release. Nitrogen balance includes zero nitrogen balance, positive nitrogen balance and negative nitrogen balance.

Nitrogen balance (NB) is an important indicator for studying protein metabolism. It reflects the relationship between the body's intake of nitrogen ( I ) and exhaust of nitrogen ( E ).

NB = I - E = I- ( F + U + S )

Intake of nitrogen can be calculated based on food protein intake. Exhausted nitrogen is unabsorbed nitrogen, including fecal nitrogen (F), urine nitrogen (U), and skin nitrogen (S). In addition to undigested food nitrogen, fecal chlorine also includes intestinal dead microorganisms, digestive juices, and intestinal mucosa exfoliated cell nitrogen. This nitrogen is called fecal metabolic nitrogen ( F _m ); in addition to nitrogen used by the body, Also included is urethral mucosa exfoliated cell nitrogen, which is called urinary endogenous nitrogen ( Um ). The body's daily nitrogen discharged from the skin, hair, all secretions, etc., as well as fecal metabolic nitrogen and urine endogenous nitrogen is about 3.5 g in total. This is the inevitable nitrogen consumption of the body, which is called obligatory nitrogen loss, ONL) ^[1]

There are three situations of nitrogen balance;

1. Zero nitrogen balance. Intake of nitrogen equals discharge of nitrogen called total nitrogen balance. This indicates that the amount of protein synthesis and decomposition in the body is in a dynamic equilibrium. This is the case for healthy adults with normal nutrition.

2. Positive nitrogen balance. The intake of nitrogen is greater than the emission of nitrogen is called positive nitrogen balance. This indicates that the amount of protein synthesized in the body is greater than the amount of breakdown. This is the case for bodybuilders, children and adolescents during pregnancy, pregnant women and the wounded during recovery. Therefore, in these people's diet, you should give as much protein-rich foods as possible. Also note: Achieving a positive nitrogen balance requires not only sufficient protein, but also sufficient carbohydrates.

3. Negative nitrogen balance. The intake of nitrogen is less than the excretion of nitrogen is called negative nitrogen balance, which means that the amount of nitrogen consumed is less than the amount of nitrogen in excreta. This indicates that the amount of protein synthesized in the body is less than the amount of breakdown. This is the case for chronic wasting diseases, tissue trauma and hunger. Insufficient protein intake will cause the body to lose weight, reduce resistance to disease, and make it difficult for patients to heal wounds. When carbohydrates are inadequate, or when they are sick or stressed, they will affect the body's nitrogen balance. When it is in a negative nitrogen balance for a long time, it will cause protein deficiency, weight loss, and decreased body resistance ^[1] .