Do you know what I like best about science? What I like best is that you can describe something so accurately that no one except a scientist has a clue what you just said. It's like speaking in secret code, only James Bond isn't around the corner hitting on yet another girl.
Technical jargon for "what are calories"
There are two types of calories, the large calorie which is what people are usually talking about when it comes to dieting and food, and the small calorie. A calorie is a unit of energy that does something.
The new definition according to the International Definition of Units is that one small calorie is approximately 4.2 joules and a large calorie is approximately 4.2 kilojoules.
The older definition is that one small calorie, or gram calorie (cal) is the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius.
A large calorie, also called: kilogram calorie, dietary calorie, nutritionist's calorie or food calorie (Cal or kcal) is the approximate amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. So if you know the metric system and was paying attention to the definition of a small calorie, the large calorie is equal to 1,000 small calories or one kilocalorie.
Clear as mud? Exactly. Gotta love science! :)
To make calories even more confusing
To make matters even less clear, the definitions are not precise due to the difficulties in measuring said definitions and I will spare you the other definitions that have come about trying to make things more precise for science and thus more confusing to the average person.
The average person ALSO has at their disadvantage that the large calorie and small calorie are used inaccurately, meaning that they are used interchangeably, but they shouldn't be.
I will be using the definition of a large calorie every time I refer to "calorie" unless I state otherwise.
So let me put the definition into terms that hopefully will make a little more sense to you. However I simply must point out that my definitions are NOT accurate generally speaking and are being used for no other reason than to give you a point of reference that will [hopefully] make more sense to you than the science definitions. In other words, I'm going to use metaphors.
Perhaps you can then take the science definitions and my metaphors and make sense of science. I wish you luck. :)
Do you, or did you, ever play video games? If so this metaphor is for you! Think of a calorie (a large calorie, remember?) as a hit point, health point, or an energy point, in your favorite video game. When you picked up an energy pack, or a health pack, you gained so many energy/health points. That's like eating a calorie. One calorie in equals one health or energy point added.
The problem of course is that most foods have way more than one calorie. So if your favorite candy bar has 200 calories, that's 200 health or energy points you've consumed when you ate that delectably sweet goodness and in a candy bar those calories sure aren't health points!!
Now in our example game, when you got shot, or fell, or something bad happened to you, you lost a health point or an energy point. Actually you probably lost lots of them depending on what happened, but that's beside the point. That's what it means when we talk about burning calories.
Whether you are running, lifting weights, lifting the television remote, walking to the fridge for another candy bar, or whatever, you are burning a certain number of calories. The amount of calories of course depends on the activity and the intensity of the activity.
Walking to the fridge to get a candy bar is one thing, running from the big mean dog who wants your candy bar is quite another. ;)
If video games were not, or are not, your thing then here's my last attempt. Eggs. Think of a calorie (a large calorie) as an egg. Pick up one egg, you've consumed one calorie. Now just so we are clear, if you eat an actual egg you are consuming approximately 80 calories depending on how you cooked your egg. For our example, and our example only, we are PRETENDING that one egg equals one calorie.
So if you throw an egg, that's like burning a calorie. Pick up an egg, consume a calorie, throw an egg, burn a calorie. Pick up two eggs, consume two calories, throw two eggs, burn two calories. See how simple that is?
We will assume that you are throwing your eggs at a canvas in order to make modern art. :)
Of course in real life, in case you skipped the video game explanation, what you eat has far more than one calorie and what you do burns more than one calorie. A candy bar is often over 200 calories, running from the kid trying to steal your candy bar can burn over 140 calories depending on your weight, how fast you were running and for how long you were running.
Losing weight by counting calories
This is something that will need it's own post, so I'm not going to go very deep here. It's a big topic in and of itself and far more complicated than these last couple of paragraphs.
The basic idea is that in order to maintain your weight, you burn as many calories as you consume. If you want to lose weight, you burn more calories than you take in. If you want to gain weight you simply eat more calories than you use.
You can use a calorie counter to help you keep track.
Now one of the biggest problems with that is that it's just counting calories, not nutrition. You can get 200 calories from eating a candy bar or you can get 200 calories from eating fruit, but only *one* of those food sources is actually good for you.
As always, you need to keep proper nutrition in mind and please please PLEASE consult with a medical professional or nutritionist BEFORE you just start counting calories.