Fasting helps tremendously, but one needs to be very much aware that one is not destroying the body. No condemnation should be in the mind; and there is the problem because almost all religions have condemned the body. Their original founders were not condemners; they were not poisoners. They loved their bodies. They loved the body so much that they always tried to purify it. Their fasting was a purification.
Then came blind followers, unaware of the deep science of fasting. They started fasting, blindly. They enjoyed, because mind is violent. It enjoys being violent with others, it enjoys a power, because whenever you are violent with others you feel powerful; but to be violent with others is risky because the other will retaliate. Then there is a simple way: to be violent with your own body. Then there is no risk. The body cannot retaliate. The body cannot harm you. You can go on harming your own body; there is nobody to react. This is simple. You can torture and enjoy power—that now you control your body; the body doesn’t control you.
Fasting for purification
If this fasting is aggressive, violent, if there is anger and destructiveness; then you miss the point. You are not purifying the body; you are in fact destroying it. And to clean a mirror is one thing and to destroy the mirror is another. To clean the mirror is totally different, because when the mirror is clean of all dust, pure, you will be able to look into it—it will reflect you. But if you destroy the mirror, then there is no possibility to look into it. If you destroy the gross body you lose all possibility of contact with the second, the subtle body. Purify it, but don’t be destructive.
And how does fasting purify? Because whenever you are on a fast the body has no more work of digestion. In that period the body can work in throwing out dead cells, toxins. It is just as one day, Sunday or Saturday, you are on a holiday and you come home and you clean the whole day. The whole week you were so engaged and so busy you couldn’t clean the house. When the body has nothing to digest, you have not eaten anything, the body starts a self-cleaning. A process starts spontaneously and the body starts throwing out all that is not needed, which is like a load. Fasting is a method of purification. Once in a while, a fast is beautiful—not doing anything, not eating, just resting. Take as much liquid as possible and just rest, and the body will be cleaned.
Fasting for rejuvenation
Sometimes, if you feel that a longer fast is needed, you can do a longer fast also— but be deep in love with the body. And if you feel the fast is harming the body in any way, stop it. If the fast is helping the body, you will feel more energetic; you will feel more alive; you will feel rejuvenated, vitalised. This should be the criterion: if you start feeling that you are getting weaker, if you start feeling that a subtle trembling is coming into the body, then be aware—now the thing is no longer a purification. It has become destructive. Stop it.
Fasting conditions
But one should learn the whole science of it. In fact, one should do fasting near somebody who has been fasting for long and who knows the whole path very well, who knows all the symptoms: if it becomes destructive what will start happening; if it is not destructive then what will happen.
After a real, purifying fast you will feel new, younger, cleaner, weightless, happier; and the body will be functioning better because now it is unloaded. But fasting comes only if you have been eating wrongly. If you have not been eating wrongly there is no need for fasting. Fasting is needed only when you have already done the wrong with the body.
Excerpted from Yoga: The Science of the Soul by Osho