In plain words
All the physicians warn that health is spoiled by the food we take and the way we live, but they do not explain clearly what food means. Whatever we experience and take in through the five senses: all of it is food. Only what is taken in by the mouth is called food; but the sights the eyes see, the things the ears hear, the smells we breathe in, the touch we feel: all these are food. These too are nothing less than root causes of the body's health! On seeing certain sights the stomach seems to turn and vomiting comes on; on hearing certain things a man is struck at once as if by a shock and falls down; and smells and touch bring on indigestion: so the doctors say. However much a healthy body matters to a healthy mind, a healthy mind too matters just as much to the health of the body.
Food should be tasty to the mouth and should give contentment and gladness; it should not be too hot with spice or too salty; you must keep ever in view the purpose for which God has granted you the body; and, never forgetting the goal of life, you must nourish it and tend it with care until you reach the shore. For sādhakas, rather than rājasic and tāmasic food, sāttvic food is the one most needed. The mystery of creation is a most wonderful thing. Men are able to judge the good and bad only of the things they can see, but they are unable to judge the merits and faults of what lies beyond sight. One thing you must know above all: even from every object, the subtlest particles and atoms keep going out at all times in the form of waves; from a point no bigger than the tip of a needle some lakhs of atoms go out; and since these are so very subtle, people cannot see them.
Put a piece of camphor in a tin, and even if you close the lid, after some time it is all gone, is it not? What is the reason for this? It is the very atoms that keep streaming out of it in an unbroken flow that brought about its end. The fine particles given off by other people's bodies reach the air and enter your bodies with the air you breathe in. In the same way, lakhs of fine particles are going out from your body too; and so everyone is ever carrying on these two actions, giving out and taking in. For the body's strength and health to wane, to dwindle or to grow, for all of it, these two actions alone are the root causes.