Digestion, energy, and fat storage for dummies

WARNING, this may get a little long.

So here is a simple primer for people who don't really understand why we have to eat the way we do in order to lose weight. This is a highly "dumbed down" explaination, so for any chemistry majors out there, bear with me, this is for the layman and I don't want to bog it down with too much technicality. I feel that practice with no knowledge is useless, and if we know the why and how of it, eating right becomes easier to do and understand. It removes the frustration level with your body, knowing why you are or aren't losing weight is as important as doing it.

3 main categories:

intake/digestion:
The food we eat breaks down (categorically) into 3 main groups; fats, protein, and carbohydrates. There is a fourth that is fiber, but fiber is in-digestable (mostly); still good for you as it passes through the system, but it causes the food in your stomach to take longer to process (which is good).

All 3 of these categories are important, protein can either be used directly as a building block for muscle and lean tissue, fats are important for brain health and breakdown for use in building cell membranes and help with cardiovacular health(heart), carbs are the energy your whole body uses.
It's important to note that all three types can be broken down for energy, carbs are just the easiest for your body to break down so usually used or converted to fat first. The body will digest food, use what ever energy and proteins/fats it needs immediately, then put some into the blood stream as free energy (cholesterol, which is a mix of fat and sugars), and store the rest as adipose (body) fat.
Also note that while all three types can be broken down for energy if needed, protein and fat are broken down in the organs, which produces side products which, if over indulged, can have averse effects (hardening of the liver, kidney stones...etc)

energy usage:
Once your body starts digesting, the 3 main intakes are broken down into composite parts, proteins (amino acids) are delivered to the liver or directly to places that need them, the liver will break them down. Fats are turned into cholestorol, or delivered right to places that need them, and carbs are broken down into simple sugars for immediate energy, or recombined into adipose (body) fat and stored for leaner times. The less complex the carbs, the faster the body breaks them down. The body can only use a certain amount of energy at any given time (metabolism), all extra is stored as fat or free sugars in the blood. This is why simple carbs are bad for you, they are very fast to metabolize and thus much of it is stored.

stored energy usage:
If there isn't enough energy, the body will use the EASIEST available stored energy. In people with excess fat, that is usually what is used. In people with less fat, or "old" fat, sometimes, protein and lean tissue are easier to break down. This is why large deficits are not good for people near a healthy weight, because even though protein breakdown is more complex then fat breakdown, if the fat is too far from a viable transport (the blood stream) it will not be used primarily, or there isn't enough fat to cover the need, and higher levels of lean tissue are used.

Conclusion:
I wrote this to clarify WHY we eat what we eat. The body is a perpetual motion machine, everything is a gray area for the body, nothing is done 100% or 0%. If you are trying to burn fat, you will always burn a little lean tissue, if you are eating complex carbs, some will almost always be stored as fat. Etc. be aware of this as you make choices, know where you are as far as weight health, if you're not overweight, then eating very low calorie diets, or eliminating one of the 3 main food types can be harmful, know that "old" fat will take a long time to remove, and while doing so, you will burn some muscle as well (which is why exercise is important along with diet, you want to build muscle while eating a caloric deficit)

I tried to keep this simple, I realize it's a complex process, and I've left out a lot to make it half way understandable, but feel free to ask if this is still confusing.

NOTE: I'm not a doctor, I just do lots of nerdy research. If you have specific questions about your own body, you might consider having a session with a certified dietician or at least a doctor (although I have less confidence in doctors because, while they are usually very good at General health, specifics like food, aren't their speciality. It's akin to asking an electrician about the insides of a DVD player, he may know the basics, but not as much as the engineer who works on them every day)

Hope this helps

-Banks