The Body:
 

Here is a brief overview on how the body works. I am going to keep it simple. The body basically needs air, fuel and water to function. The fuel is what gets us in trouble. But, if we can take in more air and water, the fuel will burn more efficiently. Everyone's body is different and no two can act the same. It is a crying shame that one person can eat a whole pizza and look like they cannot gain a pound and some can eat a slice and gain 20 pounds. But nonetheless, it is still an efficient machine that can burn fuel effienciently. Finding that type of fuel that your body can burn effienciently is a trial and error basis.