Nitrogen balance is the ratio of the quantity of nitrogen coming to our organism with the food we eat and to the quantity of nitrogen excreted from it. Since proteins appear to be the main nitrogen source of our organism, it’s possible to consider the ratio of proteins that our organism gains and destroys in accordance with its nitrogen balance; and this information is necessary to know whether muscle growth takes place.
There is a certain connection between the amount of nitrogen that our organism consumes with food proteins and the amount of nitrogen that our organism excretes. Increase of protein intake automatically increases the quantity of excreted nitrogen. In case of correct nutrition, an adult’s organism, as a rule, excretes the same amount of nitrogen it gains. This state got the name of nitrogen balance. You should remember: we mentioned before that our organism always strives for constancy (homeostasis). That’s why this kind of balance is a normal state for most people. If you increase the amount of food proteins nitrogen balance will soon be recovered but at a higher level. So, the actual result of nitrogen balance lies in the fact that our body always strives for such a sate when nothing happens: we neither grow nor lose weight.
We talk about positive nitrogen balance in cases when nitrogen intake exceeds its excretion. In this situation protein synthesis prevails over its decomposition. Positive nitrogen balance takes place always when our muscles grow; scientists say that in this situation anabolism (growth process) dominates over catabolism (decomposition process).
Proteins are not stocked up in our organism; that’s why when they come to it with food in plenty, only a part of them is used for muscle growth and the rest part is used for energy purposes. That’s why it’s simply a money waste to provide our organism with excess proteins because high-quality protein food costs a lot.
In cases when the quantity of nitrogen excreted from our organism exceeds the quantity of gained nitrogen we talk about negative nitrogen balance. It takes place during proteinic starvation and also in cases when our organism doesn’t get certain amino acids necessary for protein synthesis.
The process of protein decomposition in our organism never goes on uninterruptedly. The degree of protein decomposition is conditioned by the nature of our nutrition. Minimal protein expenditure takes place in case of carbohydrate nutrition under proteinic starvation conditions. In this situation the quantity of exctered nitrogen can be three times less than under conditions of complete starvation: carbohydrates are saving proteins in this case.
Negative nitrogen balance occurs in cases of complete absence or shortage of proteins in food as well as when consumed food contains deficient proteins. It can also happen when protein intake amount remains normal but organism protein needs increase significantly. In all these cases proteinic starvation occurs.
In case of proteinic starvation, even if our organism receives enough fats, carbohydrates, mineral salts, water and vitamins, the process of gradual body weight loss starts caused by the fact that expenditure of muscle proteins is not compensated by proteins received with food. Proteininc starvation is especially difficult for a growing organism that in this situation not only starts losing body weight but also faces catabolism caused by shortage of plastic material necessary for muscular cells construction.