Those wily Vipassana adepts who ran the meditation center in Northern California were onto something. The daily meal regime varied but largely adhered to "temple food," foods that were blander, lighter, and easier to metabolize such as fruits and veggies, rice, beans, oatmeal, and the like.
Then they'd go and play a trick: for one of the meals they'd sneak in something heavy, like some delicious and greasy plate of macaroni and cheese to teach the meditators a lesson. Grateful for the indulgence, the meditators would chow down, and experience the heavy digestive load and its cognitive effects, blunting sensitivity to the sensations and throwing off one's focus with the racing heart and heavy breathing of intensive metabolism.
It already takes a certain sensitivity to notice such changes; an inclination towards meditation or deep thought perhaps. Or perhaps an affliction makes the consequences of one's diet much more stark and noticeable when one strays. You see preferences for "temple food" or at least simple and mild food like rice back to at least the ancient Greeks; the perception has been around for some time.
But this relationship changes when the flow of energy changes as well. Temple food works great for a largely contemplative life. However when it comes to hard labor, try concentrating when that voracious hunger takes hold emanating from a depleted body, and eating a light temple diet doesn't satiate. That heavier load becomes desirable when one is concentrating energy expending muscle power.
The brain is quite energy intensive itself, but the energy and resources it takes in are of a different nature than that of the body; it is a different region, with different concerns, but which are also bound with those of the body's, so that a given balance of the regions, how those respective regions are fed and reproduced, whether those regions are getting the proper nourishment in proportion to their depletion, and how they relate to each other and give rise to a particular consciousness, make up an important part of what you are.
