Ok, seriously. Why is there no feature to configure so that manpower and colonies CANNOT push food into the negatives in my system?
Or is there a feature and I'm just blind?

You can't prevent base manpower and some food being sent out to outposts, but you can destroy buildings that consume extra food for more manpower. You can also choose which system sends food to an outpost, so as to not overload one particular one (typically your starting system). 

Problem was, the system that provided the most food also went into negatives, for just 1 outpost, which meant I lost pops... There should be a choice to prevent this, to only send as much food as you have, even if it takes the outpost longer to become a colony