The way I understood it you need food based on what you are, as in species, however the astral plane is weird. Like the "corruption" effect of the nine hells, the astral plane is mostly a mystery but entropy and other human sciences are are....warped? Changed? Don't exist in some cases? I'm actually not sure. I know the general stuff but as a core concept I don't know. Time for some things like hunger halt, but time still moves on generally for other things. This discrepancy has side effects. Assuming you're in the astral plane physically and not projecting.
Hope I have that right. Not 100 on that.
When I first heard Gith were not only confirmed but was part of the main plot, I wanted to make a Gith barbarian pirate with my own astral ship to hunt Mindflayers and treasure hunt across the astral. Boy did that go south when I learned more about bg3 and Gith in general. Lol oh well.
I died a little when I saw the scene with Laezel describing "The Tears" and her creche.