There are a chain of events where food moves from the gas station to the gas tank through the fuel line to the carburetor. Ultimately the purpose of the whole process is to drive the car. If it were to for your need to get to work there would be no point in having a gas tank or fuel line at all.
Every action of the cells in your body draw on its’ batteries contained within the cells. The batteries have to be recharged in order for the cell to function, and the primary was is the burning of food. Like the car, the food moves from the outside to the mouth or lungs, through different organs to the blood, and ultimately into the cell. If it were not for the cells activity, there would be no need for a stomach or mouth etc. The organs can only be understood in the context of their actual purpose.
So there is a sort of chain of events eventually leading to the fuel being burned. The most relevant event however is the penultimate event of the fuel actually being burned which is based on the the actual activity of the engine or cell. It is the interaction between the actual activity of the cell which dictates the rate at which the batteries have to be recharged, which dictates the appropriate flow of fuel into the cell. In the context of the necessity of this flow, everything ‘upstream’ will make sense. This is so powerful to understand that we can draw a simple diagram and use it to show advanced concepts surrounding nutrition, training, pathology, and learning.
The fuel line delivers nutrition to the engine at slower or faster rates. The engine eats the fuel proportional to how hard it is working. A hard working engine requires a high rate of flow of nutrition which is in the form of sugar. The engine must be able to slow down for periods of time in order to recover from the hard times, and during those times the flow of nutrition must be slow. The source of the slow nutrition potentially includes fat which is burned by the oxygen. Whenever the flow exceeds what the engine is eating, the excess is diverted in the form of disease or a backlash which takes the form of fatigue or is stored as fat. When theses systems are coordinated, one has energy all day and sleeps at night, learns and performs optimally without being bored or overwhelmed, in addition to many other benefits at virtually no cost.