What the heck are calories anyway

So the latest "fad" is calories. Every other person is talking about that as if it were the dreariest evil to have possessed humans. Even kids in Gymnasiums, Playgrounds and eventually Social Media, are tracking like pros. How cool is that?

Really, that's bat-shit crazy. Rule of thumb being, understand and act and not to act what you do not understand. So here's a crash course.

Calorie itself is a defunct unit of measurement of energy (heat really) and defined as the amount of heat required to increase the temperature of 1 gm of water by one degree (at one atm. pressure, but that's a separate topic). It's since been replaced by Joule but is still used widely in food industry. 

Actually, what food industry calls a Calorie is really a KiloCalorie. A single small calorie is just too little energy to be of any significance.

Considering that it was a unit of heat, it was actually calculated thus, by burning food to raise temperature of a Kg. of water by one degree. Now our body doesn't burn food, does it? Even today when we talk about calories provided by food, it is usually derived based on heat produced by burning components of that food product in a calorimeter.

Moreover, how many calories does a food product produces for you, will depend on one thing that is "you". How efficiently your body metabolize that food is what matters?
So do we ditch it all? No, not really, just be realistic.

What this all implies is that when a particular food product mentions so many calories, it does not really mean it will provide you with that much energy. A lot goes into metabolism and on an average, a human body is just 28-30% efficient in actual energy conversion.

A very simple consideration would be, how much energy do I spend in metabolizing a particular compound. Oh yes, metabolism itself consumes energy, and there goes one component explaining why our bodies are so inefficient in energy conversion.

What we need to consider instead is what we are eating and where does those calories come from, in that food. For example, Carbohydrates are metabolized with highest efficiency while metabolizing Proteins require a lot of energy and thus results in very low energy output.

So next time, you count calories, stop. Rather take a good look at what you're eating.

Oh! and stop believing in those memes talking about how much you need to walk, swim, run to burn a glass of hot tea. There's no one size fit all answer to it because energy required to move a body from point a to b, depends on weight of the body, resistance due to friction, mechanics of the movement and initial torque requirements and lot more. 

And thus we conclude, Physics is the answer to everything...