In Dune, we learn from the Duke that one of the main food sources is something called 'chemavit'. As far as I can tell it's not mentioned elsewhere in the novel(s).
Again, the Duke faced his son. “Arrakis has another advantage I almost forgot to mention. Spice is in everything here. You breathe it and eat it in almost everything. And I find that this imparts a certain natural immunity to some of the most common poisons of the Assassins’ Handbook. And the need to watch every drop of water puts all food production– yeast culture, hydroponics, chemavit, everything –under the strictest surveillance. We cannot kill off large segments of our population with poison–and we cannot be attacked this way, either. Arrakis makes us moral and ethical.”
Is there any evidence (i.e. not guesswork) as to what this substance is?