The Three
Worms are three
parasites that live in the
intestines of all people according to
Daoism (
Taoism). These parasites are the mythological explaination of why Daoists don't eat
grains.
The Three Worms are demons that live in your intestines, feeding off the decay in your body. They also are responsible for decomposing your body after you die, and they want you to die soon so that they may consume you. Grains are basically waste according to this doctrine, and as your intestines digest the grains, the Worms eat the waste produced. They grow strong from the grains and can feed on the rest of your body, causing you to die more quickly.
The Chinese, of course, make no bones about the fact that long life is a high priority, especially when one desires to be a highly attained Daoist. So, to gain long life, you must starve the Three Worms by abstaining from grain. This is in addition to abstaining from meat and alcohol. The is conspicuous of Daoists, as the diet of China has always been predominately grain. Grain includes rice, wheat, and even beans. So, the Daoist diet consists of basically vegetables as fruits aren't common in China.
Here is some classic text to prove I'm not insane:
From Taishang lingbao wufuxu (Explaination of the Five Talismans of Numinous Treasure)
The Third Immortal King told the Emperor:
"You attain the Tao by avoiding all grains. You will never again have to follow the rhythm of the moon and plant or harvest.
"Now, the people of mysterious antiquity, they reached old age because they remained in leisure and never ate any grains.
"As the Dayou zhang (Verse of Great Existence) says:
The five grains are chisels cutting life away,
Making the five organs stink and shorten our spans.
Once entered into our stomach,
There's no more chance to live quite long.
To strive for complete avoidance of all death
Keep your intestines free of excrement!"
I should say this is not universal, nor is it an absolute. I have read many accounts where a Daoist ate rice or begged for rice. Abstaining from grains seems to be most important as a precursor to purification rites and rituals, such as ingesting elixirs, long meditations, and fasting.
So then, why do Daoists have such a diet? Abstaining from grains probably stems from the fact that very little else was in the Chinese commoner's diet for a long time. Rice, wheat, and beans were the easiest to grow in most climates and they were most nourishing for a large Chinese family. However, they do not make a balanced diet alone, where as vegetables alone are very balanced. Also, since most families didn't grow lots of vegetables, this meant that those in the Way were responsible for growing their own or finding them naturally. Monks generally had large gardens, and even a Daoist following the Way alone usually has a small garden for himself.
I have asked only one master about this because he understands that the Way is formless and that the scripture is not the only way of attaining it. He said, "In old China, everyone ate grain. In that time, everyone was sick from many different afflictions, and the Daoists were healers. They would keep roots and plants that were needed to cure the people. They saw that grain caused the illness, and the plants cured them. So from their medicine, they formed their diet. They did not simply eat anything they could find, they ate plants which separately nourished the five organs. It is not bad to eat grain, but it is not necessary, and if one relies on grain as their diet, the body will get sick."
I personally eat grains, although I eat many more vegetables. I also drink alcohol. Most other Daoists I know inside and outside China also eat grain, so I believe that this belief has given way to a more moderate diet. Of course, meat is still definitely off the menu and probably always will be.