Enteral / dietary calories

Calculate total calories and macronutrient distribution from grams of carbohydrate, protein, and fat.

What is this for?

Enteral and dietary calories use the Atwater factors: carbohydrate and protein each supply 4 kcal per gram, fat supplies 9. Knowing the distribution matters as much as the total — a feed meeting the calorie goal can still be badly short on protein.

How to use it

Enter the grams of each macronutrient. For a commercial tube feed, take these from the product label and multiply by the number of cans or the volume delivered.
Optionally enter the patient's weight to get calories and protein per kilogram, which is how nutrition goals are usually written.
Compare the distribution against the goal — protein is commonly the shortfall.

Worked example

A day's tube feeding delivers 200 g carbohydrate, 80 g protein, and 60 g fat to a 70 kg patient. Calculate the total calories and the protein per kilogram.

Answer: (200 × 4) + (80 × 4) + (60 × 9) = 800 + 320 + 540 = 1660 kcal, which is 23.7 kcal/kg. Protein is 1.14 g/kg/day.

Clinical pearls & pitfalls

Fat carries more than twice the calories per gram of the other two macronutrients, so small changes in the fat content move the total disproportionately.
Protein calories are usually counted toward the total in enteral nutrition but excluded when calculating the non-protein calorie to nitrogen ratio, because protein is intended for synthesis rather than fuel.
Alcohol supplies 7 kcal/g and is not included here. In a patient with significant alcohol intake, the calorie total from food alone understates energy intake substantially.
Fibre-containing formulas contribute some calories through colonic fermentation that the Atwater factors do not capture.

Assumptions & limitations

Uses the general Atwater factors. Manufacturers may state slightly different caloric densities for specific formulas — use the label figure when it is available.
Calculates delivered nutrition only. It does not assess whether the amount delivered is appropriate, and does not account for feed interruptions, which commonly cause a 20–30% shortfall against the prescribed volume.
Excludes alcohol and does not account for propofol, which supplies 1.1 kcal/mL of fat and is a substantial hidden calorie source in intensive care.

References

McClave SA, et al. Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient: SCCM and ASPEN. JPEN J Parenter Enteral Nutr. 2016;40(2):159-211.
Merrill AL, Watt BK. Energy value of foods: basis and derivation. USDA Agriculture Handbook No. 74.