Since we've recently been exploring grains and herbs and diet more generally, seems worthwhile also to mention bigu -- a Taoist practice which refers sometimes to the complete abstinence from cereal grains, and in other contexts to the more dramatic situation of going entirely without solid or liquid food.
In the latter case, the bodymind undergoes a "phase change" (of a similar sort, perhaps, to that of Tai Hsi - umbilical breathing?) which allows it to draw energy directly from the qi of the environment -- the air and sunlight -- as well as from the body itself, hence requiring no other external forms of dietary nourishment.
The following poem -- by Taoist adept Sun Bu-er -- points to the practice of abstaining from all cooked foods (avoiding "mixing [the food] with smoke and fire"), which presumably would include cooked grains.
Once you can feed on the living energy,
Your lungs will be in an extraordinary state of clear coolness.
Forget the spirit, and there are no appearances to cling to;
Merge with the ultimate, and the existent emptiness is gone.
For breakfast look for wild taro roots;
When hungry at night, pick wetland mushrooms.
If you mix in smoke and fire,
Your body will not walk on the jewel pond.
Taoist practitioner Eve Adesso offers a fascinating account of her own quite spontaneous entrance into a bigu state, which she defines in the following way:
"The term bigu denotes an advanced qigong state during which the practitioner is able to maintain his or her normal activities without eating or drinking (and sometimes sleeping) for long periods, in some cases for several months and years at a time."
For Ms. Adesso, this came on the heels of an intensive Kan & Li qigong retreat. In the weeks following the retreat, she "noticed that the less I ate, the better I felt. So, I stopped eating." She continues by describing the utter strangeness of the situation:
"The first week was disorienting to say the least. The lifelong habit of eating is a strange thing to revolutionize. Anxiety about being different would alternate with the feeling that something miraculous was happening. I received insight after insight on the priorities of my life. I couldn't treat myself like a 'feed me and I work' machine anymore. I figured out how to cut back on working and still have what I need. My qigong practice became my daily bread, my food, my life."
She does mention that she "continue[d] to take blue green algae and tonic herb teas such as reishi mushroom and ginseng." After a period of detoxing and initial weight loss, her weight stabilized at its "ideal," she felt more energized than ever before, and more sensitive (i.e. attuned in subtle ways to her surroundings).
The responses from (non-qigong) family members, friends and colleagues were, however, not always supportive -- and frequently included (perhaps quite legitimate) concern, as well as criticism and even condemnation. In a moment of "soul-searching," she invoked inner guidance, and in the context of a meditation session received a very clear response:
"In my meditation I asked for insight and was answered......... with a cosmic symphony of blooming harmonics. The sound entered every pore and massaged every cell, whispering, singing, shouting 'You are loved, you are loved, you are loved.' It took my hand and led me into the infinite void, into an emptiness that is so full, so vibrant and so teeming with life as to satisfy all hunger for eternity. There I bathed in a mystic dew charged with serene passion and sublime sexuality. O paradise! How can I do you justice? Your splendor eludes capture even by the otherworldly art of poetry."