Amino Acids, Proteins and Porphyrins
In a critically ill patient Amino acid supplementation will maintain positive nitrogen balance by?(AIIMS May 2008)
|B||Increased protein synthesis|
|C||Decreased protein degradation|
|D||Both, by decreased protein degradation and increased protein synthesis|
a. In normal adults, nitrogen intake matches nitrogen excreted. Positive nitrogen balance, an excess of ingested over excreted nitrogen, accompanies growth and pregnancy.
b. Negative nitrogen balance, where output exceeds intake, may follow surgery, advanced cancer, and kwashiorkor or marasmus.
c. The state of protein nutrition can be determined by measuring the dietary intake and output of nitrogenous compounds from the body.
d. Although nucleic acids also contain nitrogen, protein is the major dietary source of nitrogen and measurement of total nitrogen intake gives a good estimate of protein intake (mg N × 6.25 = mg protein, as nitrogen is 16% of most proteins).
e. The output of nitrogen from the body is mainly in urea and smaller quantities of other compounds in urine and undigested protein in feces, and significant amounts may also be lost in sweat and shed skin.
f. The difference between intake and output of nitrogenous compounds is known as nitrogen balance. Three states can be defined: In a healthy adult, nitrogen balance is in equilibrium when intake equals output, and there is no change in the total body content of protein.
g. In a growing child, a pregnant woman, or in recovery from protein loss, the excretion of nitrogenous compounds is less than the dietary intake and there is net retention of nitrogen in the body as protein, ie, positive nitrogen balance.
h. In response to trauma or infection—or if the intake of protein is inadequate to meet requirements—there is net loss of protein nitrogen from the body, ie, negative nitrogen balance.
i. The continual catabolism of tissue proteins creates the requirement for dietary protein even in an adult who is not growing, though some of the amino acids released can be reutilized.
j. Nitrogen balance studies show that the average daily requirement is 0.6 g of protein per kilogram of body weight (the factor 0.75 should be used to allow for individual variation), or approximately 50 g/d.
k. Average intakes of protein in developed countries are about 80–100 g/d, ie, 14–15% of energy intake. Because growing children are increasing the protein in the body, they have a proportionately greater requirement than adults and should be in positive nitrogen balance.
l. Even so, the need is relatively small compared with the requirement for protein turnover. In some countries, protein intake may be inadequate to meet these requirements, resulting in stunting of growth.
There Is a Loss of Body Protein in Response to Trauma & Infection
a. One of the metabolic reactions to major trauma, such as a burn, a broken limb, or surgery, is an increase in the net catabolism of tissue proteins.
b. As much as 6–7% of the total body protein may be lost over 10 days.
c. Prolonged bed rest results in considerable loss of protein because of atrophy of muscles.
d. Protein is catabolized as normal, but without the stimulus of exercise it is not completely replaced.
e. Lost protein is replaced during convalescence, when there is positive nitrogen balance.
f. A normal diet is adequate to permit this replacement.