When planning menus, it seems like the math doesn't add up from time to time. Here are some assumptions:

1g carb = 4 k/Cal
1g fat = 9 k/Cal
1g protein = 4 k/Cal

Now, when I look at an item, (say John Stone's pineapple info), I see the following:

150g Pineapple = 72 k/Cal
Carbs = 19.5g
Protein = 1.5g

If I reverse the math, and do the following...

150g Pineapple = (19.5*4)+(1.5*4) = 84 k/Cal

...I see a 12 k/Cal surplus.

It seems like the total k/Cal for any given food drifts either up or down when you reverse the math.

Take, for example:

8oz Egg Whites = 120 k/Cal
Carbs = 4g
Protein = 24g

8oz Egg Whites = (4*4)+(24*4) = 112 k/Cal

This, ultimately, has a small impact on the macronutrient percentages.

This question is somewhat academic; obviously if you're getting results, splitting hairs is sort of meaningless.

But since I'm enjoying the educational aspect of fitness & nutrition, could someone enlighten me? I couldn't find a post about this specific issue.

If you really want to split hairs you should send the food out to a lab :D IIRC carbs and protein aren't really 4 calories each. I think carbs a bit less protein a bit more. Close enough they both round off to 4 but not quite.

But when you are talking about natural food things get complicated. Is that pineapple an average pineapple? Maybe it's super sweet? Maybe it was picked green. Maybe it's holding more water then average.

How about those eggs? Did a super chicken make a super egg? Maybe a little bigger/smaller?

How about your scale? Is it really accurate to 1 gram? Or more likely is it accurate to something like +/- 5 grams?

You asked :spaz:

In addition, not all carbohydrates yield calories.. "Dietary fiber" carbs are not digested and do not yield energy. So a more accurate equation is (carbs - fiber) * 4 + (protein) * 4 + (fat) * 9. But even that is just an approximation.

I've heard that it's better to trust the amount of calories listed on the label than to calculate your own. Anyone want to comment on why this is (or if it is)?

In addition, not all carbohydrates yield calories.. "Dietary fiber" carbs are not digested and do not yield energy. So a more accurate equation is (carbs - fiber) * 4 + (protein) * 4 + (fat) * 9. But even that is just an approximation.

I've heard that it's better to trust the amount of calories listed on the label than to calculate your own. Anyone want to comment on why this is (or if it is)?

Few things.

First, 4, 9, etc are rounded estimates. Fats actually vary from 6 - 9 calories per gram, and carbohydrates and proteins can be higher or lower as well (depending on the size of the molecule, chemical bonds, etc).

Sometimes, labels are simply incorrect.

Vendors are allowed a margin of error. While they have to be more specific on the grams, they can round total calories.

Vendors have a choice to multiple carbohydrate grams by 4 to yield carbohydrate calories, or to go ahead and subtract fiber them multiply by 4.

Foods with fractional portions can be rounded to the nearest whole number.

If you have 10 servings with 4.4 grams of protein, you'll report 4 grams of portein and get 40 grams or 160 calories, when you really have 44 grams or 176 calories.

If a serving size is 50 calories or less, they can round to the nearest 5 calories.

If a serving size is over 50 calories, they can round to the nearest 10 calories.

If a component is <= 0.5 grams, they can round to 0.

This a common trick employed in deli meats. A serving size might be a 50 calorie slice. It's "0g" of fat and 12 grams of protein. Sounds good?

If there is really 0.5g of fat and you stack two slices on a piece of bread, you are really getting 1 gram of fat or about 9 calories - not a lot but that makes it a 10% fat by calorie food, not a 0%.

Here's an article I wrote with more information for ya:

http://www.bodybuilding.com/fun/likness30.htm

Jeremy

Thanks for the helpful responses, especially yours, Jeremy. :tucool:

Best,
E.