In this article we will discuss about:- 1. Meaning of Nitrogen Equilibrium 2. Determination of Nitrogen Equilibrium 3. Positive and Negative Balance 4. Pure Protein Diet.
Meaning of Nitrogen Equilibrium:
Nitrogen equilibrium is a state of the body in which the intake and output of nitrogen are same. This is found in the adults where growth has ceased and no more protein can be stored.
It is the minimum amount of protein that must be supplied in the diet to maintain nitrogen equilibrium. According to Chittenden it is equivalent to 7 gm of nitrogen, i.e., roughly about 44 gm (i.e., 7 × 6.25) of protein. But other observations show that it may be still lower. In the normal diet much higher quantities are given.
Determination of Nitrogen Equilibrium:
It can be determined by dietetic experiments. At first a diet of adequate calorific value containing proportionally high protein is given. So that, the nitrogen intake and output will be same. Then the amount of protein in the diet is gradually reduced and is replaced by equivalent amounts of carbohydrates and fats to maintain the calorific value of the diet constant.
With such a procedure it will be seen that if enough carbohydrate and fats be given, the amount of protein required establishing nitrogen equilibrium may be considerably reduced. Due to this property, fats and carbohydrates are called protein sparers.
Thus normal daily nitrogen excretion of 16 gm with an ordinary mixed diet can be brought down to about 6 gm by supplying enough carbohydrate and reducing protein consumption proportionally. But there is a minimum limit below which proteins cannot further be reduced, This is called the irreducible protein minimum.
The minimum protein requirement (or the ‘irreducible protein minimum’) represents the essential protein requirement of the body, which is needed to replace the loss sustained by the endogenous protein metabolism. Hence, it is a direct measure of endogenous protein metabolism.
From these considerations it will be evident that the minimum protein requirement will depend upon:
i. The amount of fats and carbohydrates in the diet,
ii. The amount of essential amino acids contained in the food protein (because it is not possible to maintain nitrogen equilibrium with ‘second class’ proteins or proteins of Tow biological value’ even if large quantities may be taken),
iii. The adequacy of the calorific value of the diet. If the diet be insufficient in quantity the subject will undergo partial starvation, more tissue protein will burn and therefore, output of nitrogen will be more than the intake.
Value of Determining Nitrogen Equilibrium:
Established nitrogen equilibrium in any subject shows the following facts:
(a) That the subject is no more growing and therefore not storing any protein,
(b) That the protein in his diet is sufficient in quality and quantity,
(c) That his diet is adequate in calorific value, and
(d) That he is not suffering from any wasting disease.
Positive and Negative Balance of Nitrogen Equilibrium:
Nitrogen balance is defined as the difference between the nitrogen taken in the food and that excreted in the faeces and urine. The intake may be more than the loss. This is called, positive nitrogen balance. It indicates that protein is being stored. This is found in growing children, pregnant women, convalescent patients, athletes whose muscles are developing.
The loss may be more than the intake. This is called negative nitrogen balance. This is found in wasting diseases, in starvation and where the protein supply is inadequate in quality and quantity (Fig. 10.115). Nitrogen equilibrium is disturbed under the above two conditions positive nitrogen balance and negative nitrogen balance.
Nitrogen Equilibrium of Pure Protein Diet:
As a rule, in the normal human subjects, who are habituated to a mixed diet, it is not possible to establish nitrogen equilibrium with pure protein food for two reasons. First, unusually large amounts of proteins have to be taken which will upset digestion, and secondly, the high specific dynamic action of proteins will increase the combustion of more tissue proteins, so that nitrogen output will be higher than the intake whatever the amount of proteins might be given.
But in those subjects who are habituated to a very high protein diet (viz., Eskimos who consume about 3.5 Kg of meat per day) nitrogen equilibrium can be established with protein alone. In carnivorous animals the same thing is seen.