Occasional lurker here.

Nohman was a normal human from Mars who became obsessed by the immense powers of Metatron manifested in Anubis; we know this from episode 19 of "Dolores, i", where he began showing the earliest signs of "metatoxication". Back then he looked pretty much human--well built even by Earth standards might I add.

We find out later in ZOE2 that Orbital Frames -and by extension, Metatron- can sustain a human body without the need for a heart and lungs. This is relevant; Nohman realized the limitations of a regular human body that would interfere with literally becoming one with Anubis (i.e. the need for a constant supply of air, the need for food, etc...) so he had his entire body replaced by an exoskeleton save for his head, leaving his brain as the only organ required to pilot Anubis. This lead to his head becoming almost death-like, as there is no blood (i.e. nutrients and oxygen) going there anymore, and is kept from decaying -and fully functional- solely by the power of Metatron (which he gets through the tail-like plug in his suit). Lastly, energy consumption by the brain would yield organic waste, which is ultimately drained by the tube that's going to his bladder (had to explain why he had a tube coming down from his head )

My 2 cents.