It's a newbie trap. It's cool when newbie try out the options to accelerate outpost growing speed but double food also often causes the supplying system to starve which leads to a decrease in population. While it can be a powerful tool when competing with others to hasten outpost growing,a newbie will have trouble figuring out the relation of 

double food to outpost -> food in supplying system goes negative -> decrease in population until they hove the food tooltip and see "food to outpost"

Suggestions are

1. warn the player when sending double food will starve the supplying system
2. allow canceling double food
3. add a line explaining why there is a decrease in population (negative food)
4. add a tutorial slide teaching player how to deal with starvation the first time it happens