Now, let's make it more complicated and talk about the International System of Units (known as the SI). Well, obviously, these are used worldwide in the scientific communities. Even though calories or kcalories is the most common measurements of food energy, the SI uses joules or kilojoules instead. I know, I know...some of you might be thinking "Hey, wait a minute! A joule is a measurement of work done!" Guess what? You're right, it is. So there's a formula (of course there is). The work energy formula goes like this:
1 joule =
the movement of 1 kilo,
a distance of 1 meter,
by the force of 1 newton
Get it? I've got the gist of it, which is what matters. A little easier is to convert from kcalories to kilojoules and that formula is to just multiply the kcalories by 4.2 to arrive at the kilojoules (kj). Now that that's out of the way, on to more interesting things to do with food energy!
Energy from Foods (aka calories).
This is oh-so dependent on how much carbohydrates, fats, and proteins a food contains. But not all of these are the same either!
To calculate how many calories a particular food has, you have to know the baseline caloric breakdown for these nutrients.
1 gram of carbohydrates = 4 kcalories of energy
1 gram of proteins = 4 kcalories of energy
1 gram of fat = 9 kcalories of energy
1 gram of alcohol = 7 kcalories of energy
Now, you probably will never have to do this calculation because most product manufacturers and plenty of weight control books/websites offer the breakdown for you but just so I get it down... the formulas to calculate a food's available energy:
Total carbohydrate grams X 4 (kcalories)= available energy
Total protein grams X 4 (kcalories) = available energy
Total fat grams X 9 (kcalories = available energy
Total alcohol grams X 7 (kcalories) = available energy
-Next, add all the available energy and you have your total.
Now, this calculation might come in handy as it helps to gauge the energy density of a food. This is NOT the same as the nutrient density which I previously discussed. Nope, this has to do with the potential energy of that food. Which means that if you were trying to lose weight, you'd want this density number to be low and not high. Remember, lower for losing, okay? So to calculate this, take the total kcalories and divide it by the total grams...
Total kcalories / total grams = kcalories per gram
And, to calculate the percentage (%) of kcalories of the separate nutrients:
Nutrient's Available kcalories / Total kcalories of food = %
So, for example... say the total calories for a food (that's all it's nutrients' calories added together) is 173 kcalories and you want to know how much of that food's kcalories is derived from fat. You know that the fat's available kcalories for the food is 81, so you divide 81 by 173. That gives you .468, and flashback to school again, you multiply that number by 100 to get a percentage (or do the fancy decimal point move thing) which makes it (with rounding) 47%. That means that the food derives 47% of it's energy/kcalories from fat! That's a lot. One should strive to limit fat intake to 20-35% of the DAILY kcalorie intake.
Now think about all these calculations and how many times we refer to the word energy. These kcalories/calories are basically potential energy - nothing more, nothing less. Think of this energy as money you deposit into your checking account at the beginning of the month. Then you pay your rent/mortgage, utilities, and other bills, you meter out spending money and then you (hopefully) take what's left and put it in savings. The bill paying is your daily calorie burn. Savings is the fat storage located all over our bodies. The fat "savings" is there for a "rainy day" and, just like your savings account, if you never draw money for those fabulous exotic vacations and just keep adding, that account grows larger and larger because, just like the bank, our bodies aren't going to say "Whoa, there partner, you're saving way too much so we're going to have to throw away some of this". Nope, as much as we'd like our bodies to reach a maximum weight savings, it's not going to happen. But, it is our responsibility (for health reasons alone) to make sure we are properly taking in energy amounts that our bodies can use to function properly without throwing the extras into "savings". Hmmm, maybe I should've compared energy intake and output as paying the right amount of income taxes so that you neither have to pay anything in April nor receive a refund...oh well, you get the idea!
I'm going to end this section here - hopefully you weren't too bored with all the math in this post :-D
All information on this blog is my own pursuit of information on the road to getting my BS in Nutrition Science and as a mode of studying. Most information and data was taken from my textbook "Understanding Normal and Clinical Nutrition" by Rolfes, Pinna, & Whitney, ISBN-13: 978-0-495-55646-6
Happy October!
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