Which step in nitrogen balance calculation involves converting protein intake to nitrogen?

Which step in nitrogen balance calculation involves converting protein intake to nitrogen?

• A. Multiplying protein intake by 6.25
• B. Subtracting UUN from protein intake
• C. Dividing protein intake by 6.25
• D. Adding insensible losses to protein intake

Answer: (C)

The conversion uses the fact that protein is about 16% nitrogen, so to get nitrogen from protein you divide by 6.25. This puts protein intake into nitrogen units, which is what you compare to nitrogen losses (such as urinary urea nitrogen plus insensible losses) in the nitrogen balance equation. For example, if someone eats 80 g of protein in a day, the nitrogen intake is 80 ÷ 6.25 = 12.8 g N/day. The overall balance then subtracts total nitrogen losses from this intake to determine whether the body is in nitrogen equilibrium. Multiplying protein by 6.25 would overstate nitrogen intake, and subtracting urinary nitrogen from protein intake or adding insensible losses to protein intake mixes units or occurs at a different step of the calculation, not the conversion step.

The conversion uses the fact that protein is about 16% nitrogen, so to get nitrogen from protein you divide by 6.25. This puts protein intake into nitrogen units, which is what you compare to nitrogen losses (such as urinary urea nitrogen plus insensible losses) in the nitrogen balance equation. For example, if someone eats 80 g of protein in a day, the nitrogen intake is 80 ÷ 6.25 = 12.8 g N/day. The overall balance then subtracts total nitrogen losses from this intake to determine whether the body is in nitrogen equilibrium.

Multiplying protein by 6.25 would overstate nitrogen intake, and subtracting urinary nitrogen from protein intake or adding insensible losses to protein intake mixes units or occurs at a different step of the calculation, not the conversion step.