The only solutions are as follows:

Upgrade farms as high as possible.

Upgrade Spring of Life (Its costly, but totally worth it.)

Upgrade Food Consumption in the Obelisk with Skull Runes.

Take food settlements as often as possible.

Try to keep only eltrich versions of units in castle, rather than normal units.

Keep as few infantry at castle as possible. Send infantry to battlegrounds to exchange for higher leveled units. Total food consumption goes down.