Inmates starving

I am having issues where about 75 of my prisoners constantly have severe need for food. I have I believe more than enough canteens, all fully staffed and with the max prisoners working in each kitchen. Every zoned area also has access to a canteen, but when meal times come around, there are the 75 or so prisoners who's food need never goes down. Any advice on how to narrow down where the problem is and how to fix it?