Energy

So, having dispatched the myths around protein and energy, the question remains: Where does the body get its energy from?

The answer is the "Kreb's cycle" (or Citric Acid cycle) which I will simplify at a great loss of accuracy:

Each of your cells has several hundred to over two thousand mitochondria* inside of them, depending on their need for energy. For instance, heart cells and muscle cells may be up to 40% mitochondria. All together, your body has over one quadrillion mitochondria that are constantly producing energy. Approximately 90% of the oxygen you breathe will be used by your mitochondria.

Your body takes the sugar or fat molecule and breaks it down to smaller units of two carbons. Mitochondria then use oxygen to break down the carbon and strip off two electrons, creating carbon dioxide as a waste product.  The electrons, in a series of chemical reactions, are attached to a phosphate molecule, which is then attached to another molecule, changing adenosine diphosphate (ADP) to adenosine triphosphate (ATP). When your muscles need energy, this high-energy phosphate is stripped off the ATP, and it becomes ADP again.  These chemical reactions require vitamins B1, B2, B3, B5, and B6; vitamin E, Coenzyme Q10; iron, sulfur and other micronutrients.

Of course, your body gets the sugar or fat from your digestive system but, unlike protein -- which is discarded if not used -- your body will happily store excess for later.

Of course, it's pretty complicated because it was designed by a blind watchmaker, but it is also very efficient, and all animals use the same basic process to create energy.

However, stripping electrons is dangerous business, because at the cellular level they can do significant damage if not controlled. Oxygen is already pretty volatile (and the reason your body uses it to produce energy), but if it picks up an extra electron it becomes a "free radical" which can rip through cell membranes,  There is some fairly compelling evidence to indicate that the entire "aging process" is actually the result of the damage of free radicals over time.  Experiments with aging rats, for instance, indicate that the mitochondria become less efficient and the cells themselves become "leaky" and less able to control the processes of what goes in or out of the cell.

Some interesting experiments were done with these aging rats to give them supplements of acetyl-L-carnitine to increase the mitochondria rate, and alpha-lipoic acid to reduce the number of free radicals, and found that within two weeks the old rats were as active as young rats.  Of course, humans aren't rats, as we discussed on the issue of protein! (I've been taking alpha-lipoic acid since I read that over 10 years ago, and I seem to have aged just fine...)

* Not to be confused with "midi-chlorians," which is the source of the Force. George Lucas is an idiot.