It's not that, it's just in this 100 player world maps there is not enough food provinces and when at war with five, along with the morale penalty of doing so, and distance to capital, it makes it almost impossible to keep food production up.
Trust me, I have L5 IC's, L3 Infra, L5 forts, on all core provinces and all barracks turned off.
Thanks for reaching out though!
Produce fewer infantry units ---- they suck food at 2x the rate of non-infantry units.
Also, have you maxed out food production in coastal provinces with L3 naval bases? They add another 30%, and you can avoid paying the full 250 tons of oil per day when they are enabled by stopping construction when they are 95-99% complete. The almost complete L3 naval bases render almost 100% of the benefit and it costs the same in daily upkeep as an L1 naval base (50 tons of oil).
Hey, Gator. If you have any questions about resource production, just ask.