The narration on "Alp-Aahaar" is very outstanding in the book. It describes that through Kriya Yoga certain sections of brains can unlock the potential to pull cosmic energy to feed one's body. Hence, a person reach a state where No food or water is needed to keep body alive/healthy/non-decay etc...
Now, that sounds like a very astonishing fact !
But, there is nothing new in the book. All such Hindu mysticism, mentioned in the book, are already revealed in Vedas, Shastras, Purans, Upnishads etc... That book has been written in a Lucid manner with nice narration for people living in scientific age. That book is a happiness shared by one seeker with other seekers. It provides inspiration for true seekers. It provides a hope that if one seeker can achieve then other seeker too can achieve the same.
Which "Khand" is achieved is a different story !
Bottom-line is Gursikhs should not get engrossed in such text too much. It should be just used for comparitive study. Other’s may use technique of Yoga, Kriya etc... Gursikhs just use NAAM.
ਨਾਮ ਤੁਲਿ ਕਛੁ ਅਵਰੁ ਨ ਹੋਇ ॥
ਨਾਨਕ ਗੁਰਮੁਖਿ ਨਾਮੁ ਪਾਵੈ ਜਨੁ ਕੋਇ ॥੮॥੨॥
Bhul Chuk Maaf.
Waheguru Ji Ka Khalsa,
Waheguru Ji Ki Fateh.