I also lost food rather unexplainable in the beginning of the game when leaving it running in between sessions. I had to restart a couple of times, because the situation had turned out to be too desperate. Then I decided to pause the game in between sessions until I got level 2 of farming. Then I monitored it for a while and left it on half-speed for an hour or two and checked again, and finally it seems to be okey to leave them at half-speed over night. Still I had to be wary, because of the food resource limit and the farmers' strange priorities. I really could not relax completely until I got level 3 of farming.