The food mechanic slows the game down? This is a strange claim to me. Every party member joins with enough food for a night, so you start the game with almost a week worth of free rests. In the course of just wandering around, I easily acquired enough food that I never had to even use the resources from my party members. I would think that food would speed the game up by discouraging you from resting every single time you use a daily spell.
I think food should be kept simple. I should not ever have to fret about food except in dire circumstances or because a map is specifically designed around the lack of food, just as most of the time players don't have to fret about rations unless it's a specific challenge of the journey they are on. Having food to prevent infinite resting is good, but it should never ruin a game.
Pillars of Eternity Deadfire has about 30 food items each with different properties. You can go find ingredients and prepare your super food if you want (and then likely end up resting again nearly immediately to clear an injury or somesuch and losing all of those bonuses). Most of the time I just end up giving everybody mariner's porridge because it is easy to get. I think putting the idea of rations in the player's head is good. I think having a situation where a player feels like they need to start over or reload an old save because their character is starving to death and can't recharge spell slots is bad. You want food to be enough of a burden that the player thinks "Hmm, I'd better press on because I haven't used enough spells to be worth a whole night of food," but never "I will never be able to feed myself tonight."