Nitrogen balance

A 22 -year-old man started to work out twice a day with the goal of competing in an upcoming bodybuilding competition. Despite his strict working routine, he continues eating a diet of fast food hamburgers and French fries. After a gain of 15 pounds, it is likely he is in a:

A. Vitamin overload

B. Negative nitrogen balance

C. Positive nitrogen balance

D. State of decreased BMR

E. State of increased BMR

Answer- The correct answer is- C-Positive nitrogen balance. The gain in weight despite strict work out signifies positive nitrogen balance.

The state of protein nutrition can be determined by measuring the dietary intake and output of nitrogenous compounds from the body, 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 x 6.25 = mg protein, as N is 16% of most proteins). The output of N from the body is mainly in urea and smaller quantities of other compounds in urine, undigested protein in feces; significant amounts may also be lost in sweat and shed skin. The difference between intake and output of nitrogenous compounds is known as nitrogen balance(figure).

States of nitrogen balance

Three states can be defined-

1)  Nitrogen equilibrium– 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.

Intake = output : N equilibrium

2) Positive nitrogen balance– when the excretion of nitrogenous compounds is less than the dietary intake and there is net retention of nitrogen in the body as protein.

Intake > output: positive N balance

Examples- In a growing child, a pregnant woman, or a person in recovery from illness there is positive nitrogen balance.

3) Negative nitrogen balance– There is net loss of protein nitrogen from the body

In response to trauma or infection, or if the intake of protein is inadequate to meet requirements there is negative nitrogen balance.

Intake < output: negative N balance

Nitrogen balance

Figure-Nitrogen balance

In the present situation, the most appropriate answer is positive nitrogen balance.

As regards other options

It is not vitamin overload. The weight gain by no means signifies vitamin toxicity.

It is not even negative nitrogen balance, there is no apparent reason for nitrogen loss .

Low BMR  is also not a possibility, it can explain weight gain but the person is strictly working out, hence it is not the right option.

Physical exercise not only influences body weight by burning calories. It also helps to raise BMR by building extra lean tissues. Lean tissue is metabolically more demanding than fat tissue. High BMR could have been a correct answer had there been no weight gain.

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