For the purposes of this question, I think dwarven meals follows a specific series of events like this:
- A dwarf starts its Eat job.
- The dwarf causes a straight-line search calculation for the nearest acceptable food product to the dwarf (it might be that preferred products are always chosen first, no matter the distance). I don't know if this search respects food quality, but I'm pretty sure it doesn't.
- The dwarf causes a terrain-respecting pathing calculation from the dwarf to the food item chosen in step 2.
- The dwarf paths to the food item, picks it up if it's still there. Otherwise return to step 2.
- The dwarf causes a straight-line search calculation for some place to eat at (a chair, possibly one assigned to the dwarf, or maybe in a meeting hall, possibly preferring chairs with free tables next to them).
- The dwarf causes a terrain-respecting pathing calculation from the dwarf to the eating spot chosen in step 5.
- If everything is still correctly ordered, the dwarf proceeds to eat the object.
Of note here is that dwarves will search for items to use in their jobs based off how close the item is to the dwarf when their job starts, not how close the item is to the job's completion point.
This means if you fill a stockpile with prepared meals and place it closer to where most dwarves work than the stockpile of plump helmets, dwarves should choose more prepared meals than plump helmets. If, however, your dining hall is off to the side of the fort, and your plump helmet stockpile is in the middle of your fort (next to the brewery in the workshop area, say?), dwarves may choose plump helmets much more often than prepared meals, which might be stored closer to the dining room (which is far out of the way for dwarves in the workshop).