I think you're the first person I've seen mention the truffle! The next update includes some more ingredients of this type, with new status effects.
With the concentrate, that fixed 350k calories was intentional, as I didn't want it to be too overpowered (whereas I'm not too worried about that in the facility, where I'm happy for people to go wild and fatten girls up to crazy weights).
The care assistants are quite painful to fatten right now, but they'll be much easier to romance in the next update as you'll be able to take them out on dates (even if you don't work at the care home).
I'll be doing a revamp of dates in the 'More Personalities' update, which will make lots of changes to how persuasion, etc work. Before that, try day trips and gifts for quickly building affection.