Is 4cal/gram for carbs & proteins an exact number?

[romaxe]

I'm asking this because I've heard some people saying carbs and proteins have 5cal/g and also..when reading the nutrient info for certain things I buy and do my 4/4/9 calorie math..it doesn't add up properly. Does anyone know if these 4,4,9 numbers are exact? or are they just approximations?

[marioMushroom]

I don't know if 4cal/gram is exact, but I know why the numbers don't add up. Food manufacturers round to the nearest 10 (sometimes 5) calories. For example, a slice of bread that says 80 calories might actually have 77.6 or 82.1.

[jynxlynx]

As per my Principles and Nutrition class notes:

Carbohydrates = 4 Calories per gram (4 Cal/g)
Protein= 4 Cal/g
Fats= 9 Cal/g
Alcohol= 7 Cal/g

Calories burn in that same order. Carb calories burn first, followed by protein and then fats. Alcohol calories burn last.

[spltend]

i've wondered this myself. I'm in pharmacy school and we use 3.4/4/10 - Dextrose/Protein/Lipid for calculating a TPN. I don't know if Carbs=Dextrose and Lipids=Fat, exactly.

But usually I just use 4/4/10 and it will come out really close to what the package says for total calories.

[rip]

I'm asking this because I've heard some people saying carbs and proteins have 5cal/g and also..when reading the nutrient info for certain things I buy and do my 4/4/9 calorie math..it doesn't add up properly. Does anyone know if these 4,4,9 numbers are exact? or are they just approximations?

No they are not exact numbers, they are rounded. Both carbohydrates and protein give slightly more than 4 calories per gram. Fat does not give 9 calories per gram either, but I'm not sure which way it is rounded.

[Jules Verne]

They are also slightly different for different foods, but close enough to 4 not to worry about it.

The fact is, when you injest a certain carb, it is not trivial to tell exactly how much energy is available to your body to 2 significant figures and may not only depend on the carb, but also on the person, what else they eat with the meal , when it is eaten etc..

These are all MINOR variations though (al least in most cases).

One reason the food labels do not always add up if the different methodologies used to estimate g of macros and total caloires (they do not always simply add up the macros, even without rounding).

[Fr3akyPhysique]

protein is also the hardest macronutrient for your body to digest, and 30% of the calories are burned just from digestion
carbohydrates take about 8% of the calories to digest them
fat is the easiest and takes only about 2% of the calories to digest them

[romaxe]

k..so are manufacturers rounding up/down the label numbers or are they using the exact numbers and we're the ones using approximations?