Hey Gamble,
This is a thread I started awhile ago (nobody really knew much about it):
http://bbs.evony.com/showthread.php?t=183206
I play on one of the newer attack servers, and when players run out of food completely in all their cities, a buff appears in the top right corner next to your war horn etc, which says "troops are weakened".. Then when that player tries to farm a lvl 10 npc, they will usually lose about 70k archers.. or if they are attacked while they have the buff, they lose a lot more troops than if they had food there.
There are ways around it though ;p