Nonprotein Calorie to Nitrogen Ratio

• March 23, 2015

What Are Nonprotein Calories?

As you know, calories come from carbohydrates, protein, and fat.  One gram of carbohydrates yields 4 calories; the same for one gram of protein.  And one gram of fat yields 9 calories.  Nonprotein calories are simply the calories in the diet coming from carbohydrates and fats only.

Nonprotein Calorie to Nitrogen Ratio (NPC:N)

Nonprotein calorie to nitrogen ratio is a relationship between the nonprotein calories and nitrogen content of the diet.  Since protein is the only macronutrient to provide nitrogen, NPC:N may be used to assess whether the nitrogen (or protein) intake is sufficient to maintain muscle tissue.

A ratio of 150:1 to 200:1 is considered an adequate intake for stable patients.  For patients who may be critically ill or have difficulty maintaining muscle mass, an NPC:N ratio of 100:1 or less (higher protein intake) may be optimal.

Commit the values of 6.25 and 16% to memory.  Why?  When given the amount of protein or amino acids in the diet, you can use either of these values to determine the amount of nitrogen in the provided amount of protein.  Protein is comprised of approximately 16% nitrogen, and when converted into a value by dividing 100% by 16%, you get 6.25.

• *  If using the factor 6.25, divide the number of grams of protein or amino acids by this factor
• *  If using the 16% factor, multiply the number of grams of protein or amino acids by 0.16, which is 16% expressed as a decimal
• *  Tip:  If after calculating the grams of nitrogen, and you discover the grams of nitrogen is higher than the grams of protein, then you probably divided when you should’ve multiplied, or vice versa.  The nitrogen grams will always be lower than the protein grams since nitrogen makes up a small part of the protein.

NPC:N Example

Question:  A patient is receiving 2,200 calories.  This diet is providing 65 grams of protein.  What is the nonprotein calorie to nitrogen ratio (NPC:N)?

Solution:  The first task is to find the total calories minus the protein calories, which is known as “non-protein calories”:
65 grams of protein x 4 calories/gram = 260 calories from protein

Next, subtract the protein calories from total calories to get the non-protein calories:
2,200 total calories – 260 calories from protein = 1,940 non-protein calories

Then calculate the amount of nitrogen in this diet.
If using the 6.25 factor:  65 grams of protein / 6.25 = 10.4 grams of nitrogen
If using the 16% factor:  65 grams of protein x 0.16 = 10.4 grams of nitrogen

Finally, divide the total non-protein calories by the grams of nitrogen:
1,940 non-protein calories / 10.4 grams of nitrogen = 186.5.  The ratio is written as NPC:N, or 187:1