Measuring Energy and Its Forms

Measuring Energy

I mentioned that energy is quantifiable.  That is, we can measure it.  Over time we have come up with a number of different definable measurements.   Just like we measure, say, length as inches, yards, meters etc.  we have different ways of discussing amounts of energy.   

There are two units that are used in nutrition.  One is the Kilojoule (KJ) – named after Jame Prescott Joule (. . . ..  Not that it matters right now, but for definition buffs, it is the amount of energy needed to move a mass of one kilogram, 1 meter.   In countries other than the U.S. you will often find the energy content of foods measured in Kj's.  

In the U.S. the unit we are all familiar with is the Calorie.  The Calorie is the amount of heat necessary to heat a kilogram (about 2.2 lbs)  of water 1 degree Celsius, and equals a bit over 4 Kj.

(Word of caution, the "Calorie" - uppercase C, that is used in food energy is 1000 times as much as the "calorie" - lowercase c that often shows up in scientific research.  Although most of the science world is now unified on the joule or the Kilojoule.)

Of course the word “Calorie” brings to many of us in the modern western world a sense of foreboding, a shudder goes through our sensibilities.  We have come to dread that word and think of Calories, and therefore food energy, as a bad thing. This is because we live in a unique time in history when much of the western world suffers under the weight of excess calories rather than too few.  We will discuss this rather prejudicial view presently.  But for the time being, let’s remain clinical and, if possible, be willing to accept a broader view of the importance of food energy.

Very often you will see a food advertised as low in Calories but high in energy.  Well, this is perfect nonsense of course.  Its like saying your house is very tiny but has a very large square footage.  The implication is that this is not offering food value, but, presumably some sort of drug like caffeine that get the juices flowing, and comes about because the multiple meanings of the world "energy."

Forms of Energy

One aspect about energy that leads to confusion in every beginning science student is the fact that energy comes in several different interchangeable forms.  It routinely morphs from one form to another.  Interestingly, it is not destroyed - the amount in the universe, as best we can tell, remains constant.*(For the science buffs, Einstein pointed out that energy is also interchangeable with mass – famous equations E = mc2, but lets not go there).  It isn't born, it doesn't die, it just changes form.

In understanding food energy and what we do with it we have to be acquainted with several forms. You don't need to memorize this or anything.  Just know that they exist and that the each are of importance to our bodies and our lives.   

First: Solar energy, sometimes called radiant energy.  The sun produces staggering amounts of energy that is radiated out into the universe.  Some of it hits the earth.  That’s a good thing. 

Second: is chemical energy – this is a stored form of energy which is contained within the structure of chemicals or molecules.  And, I might add, your body.

Third: mechanical energy – the form that actually does the work.  Our bodies are constantly converting stored chemical energy into mechanical energy.  My typing on the keyboard, and you moving your eyes from left to right are examples of mechanical energy in use.

Finally: we will be discussing heat.  

All of these are interchangeable, all are measured in Kilojoules or Calories.  We will stick to Calories.

The next question is where does the energy that we get from our food, come from originally?