You would create ridiculous power users with this. 0 food buff? People will still farm, sell the food for wood/iron and create ridculous size armies. You would create a new problem in attempting to solve another. To be honest, I reckon a good thing to do is take things like transporters, ballistas, catapults and rams and make it so you need gold to upkeep them instead of food. Mechanised stuff should require gold to maintain them instead of food. This would ease some of the food issues