I tested all the listed modifiers of hunger rate (now food consumption in pawns' stats info card). Added one by one and checked how the number changed. My findings from testing:
-Malnutrition doesn't seem to be having any effect regardless of stage. This is probably a bug, since it the tooltip on the hediff claims to be increasing hunger.
-Metabolic efficiency from Biotech genes ins mistakenly listed on offsets. It's a multiplier after offsets are calculated.
-Psychic hangover has been removed and replaced with Psychic breakdown which doesn't have an effect on hunger anymore.
-Stomach implants from Royalty are OFFSETS, or at least they work as such. I have no idea whether it's a bug or the tooltip is misleading, I recall checking the defs in the game's files and seeing it written as a multiplier there too, but once inside the game it's always the first modifier applied along the other offsets.
-Sleep accelerator seems to apply in a similar manner to how beds modify a pawn's immunity gain speed, and it's also a multiplier.
-Life stages don't show up as modifiers in the info card, a lower base hunger rate is displayed instead. The numbers here seem to be correct but I couldn't test in dev mode which ages correspond to which hunger rates. Needs clarification.
All the other modifiers seem to be correct.