American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What is the relationship between protein intake and nitrogen balance?

1. 1 g of nitrogen requires 4 g of protein

2. 1 g of nitrogen requires 6.25 g of protein

3. 1 g of nitrogen requires 8 g of protein

4. 1 g of nitrogen requires 10 g of protein

The correct answer is: 1 g of nitrogen requires 6.25 g of protein

The relationship between protein intake and nitrogen balance is fundamentally rooted in the metabolism of protein in the body. Proteins are made up of amino acids, and nitrogen is a key component of amino acids. In any discussion of nitrogen balance, it's useful to consider that when protein is consumed, it is eventually broken down into its constituent amino acids. Each amino acid contains nitrogen within its structure. Specifically, the average nitrogen content of dietary protein is approximately 16%. This means that for every 100 grams of protein, there are about 16 grams of nitrogen. To convert the nitrogen content to protein weight, one can use the factor of 6.25; this factor is derived from the equation that 100 grams of protein divided by 16 grams of nitrogen results in 6.25. Consequently, it follows that for every 1 gram of nitrogen, approximately 6.25 grams of protein would be required. This understanding of the nitrogen content in protein is crucial when assessing dietary needs, especially in clinical settings where protein and nitrogen balance may be closely monitored, such as in patients recovering from surgery, trauma, or illness. The foundation of this relationship helps guide nutritionists and healthcare providers in determining appropriate protein intake to ensure proper nitrogen balance and overall health