The Daoist Immortals are often described as abstaining from grain (bigu) as part of their training and progression in the Dao
Likewise, the abstention from grain of Saints must be seen to be a fundamental technique of achieving immortality, perhaps only inferior to a magical plant or elixir that would instantly fulfill the same function as the practice of bigu. (Dannaway, Frederick R. (2009)Yoked to Earth: A Treatise on Corpse-Demons and Bigu)
I have personally observed for two or three years men, who were foregoing starches, and in general their bodies were slight and their complexions good. They could withstand wind, cold, heat, or dampness, but there was not a fat one among them. I admit that I have not yet met any who had not eaten starches in several decades, but if some people cut off from starches for only a couple of weeks die while these others look as well as they do after years, why should we doubt that the (deliberate) fasting could be prolonged still further? If those cut off from starches grow progressively weaker to death, one would normally fear that such a diet simply cannot be prolonged, but inquiry of those pursuing this practice reveals that at first all of them notice a lessening of strength, but that later they gradually get stronger month by month and year by year. Thus, there is no impediment to the possibility of prolongation. All those who have found the divine process for attaining Fullness of Life succeeded by taking medicines and swallowing breath; on this they are all in perfect agreement. A moment of crisis, however, generally occurs at an early stage when medicines are being taken and starches abandoned and it is only after forty days of progressive weakening, as one uses only holy water and feeds solely on breath, that one regains strength. (15, tr. Ware 1966:246-7)
