True protein deficiencies are very rare and do not occur in the healthy, well nourished individual. Protein calorie malnutrition is a condition due to lack of enough food to maintain health. This can result from much higher than normal protein needs or because of an inability to absorb the protein that is eaten.
Nitrogen balance is a term you are likely to hear used by your physician or nutritionist. Since protein is the only nitrogen containing macronutrient, the amount of nitrogen in the body is an accurate method of determining protein content of the body. When the amount of protein present in the diet is known and the amount of protein being excreted is known, then the amount of protein left in the body can be measured.
When nitrogen intake and nitrogen output are equal, that individual is said to be in nitrogen balance or equilibrium. This is the usual state for healthy adults.
If an individual has more nitrogen coming in than going out, that person is said to be in positive nitrogen balance. This means the buildup of tissue is greater than the breakdown of tissue. This occurs in pregnant and lactating women; growing infants, children, and adolescents; and adults who are recovering from an illness that resulted in a protein loss.