I could be totally wrong so if you think so and can provide some evidence then by all means do
So with the three different qualities, it seems that they affect different values on the food.
Essence - I'm not sure on this but I think it affects the stamina gained, as that's the only one that stays the same in those three pictures there
Substance - affects the hunger given, where higher substance = lower hunger, which in turn means you can eat more before you reach the next hunger level
Vitality - affects the FEP amounts

I'm also not eating anything and timing how long it takes for each hunger level to go down from 100% to 0% (some of this might be approximate because the times seem to get MUCH longer the hungrier you are
I got myself to 100% stuffed at 4PM on 31/8 and am tracking it from there, no eating unless I have to, If I do then I'll have to start counting again, so i'll edit this to include what I find
Getting from 100% stuffed to 100% full took 1hr 20m