DF1871: I had a similar problem during my last game (maincampaign, huge storage, huge surplus production but people get hungry and/or starving.
The Solution for me was..to build more Kitchens(The basic ones, the small Kitchens from the faithtree do't help it seems, sorry for the word but i don't know the englisch word imo) and set at least one or two on long shifts.
It seems, that the Kitchens do more then just preparing the food,i could see from the messages, that the people eat at home but they seems to gather food first and if your workers have long shifts all day...and the Kitchen(s) are only open during their working hours...
I know it doesn't make sense because i had no problems with this while i had few people, even with one Kitchen sett to normal shifts and the rest doing long shifts+builind stuff afterwards...but it helped :) I can only guess but maybe the people can gather their food from different buildings (Kitchen,Mainstorage,...) and the amount of people that can gather the food together is limited...if they work long shifts, you let them build something during the remaining hours...and then...500 people storm the Kitchen&Storehous to get food NOW..because the would like too sleep since 3-4 hours:) but only 5 people can get food together..so after a time the rest gives up :)
My problem wasnt the lack of kitchens. My population was "eating" 4000 rations per day!!! And yes i had a similar issue to yours in another playthrough, but thats insignificant overall