I agree that the planet will have food, yet if we look at human history we will see that after a time of war most deaths to the local population was because of starving, or illness caused by starvation.
Even if there has been no real large scale war between developed countries recently so we could see the effects, we can speculate that most able people will be helping with the war and this will slow down production. Even when most people know food comes from farms very few of them know the locations of the farms, or how to farm.
Also during world war 2 most countries suffered large resource scarcities, it's safe to say that after a planet is conquered it will undergo a recovery stage.
The thing about food is how it's processed, when food is considered bad for a animal it means that the animals digestive system can't break it down into fuel. A combination of acids and digestive enzyme allow food to be broken into the needed chemical fuels.
All combos of acids and enzymes can break down some basic elements even if some are slow at it, so a all purpose food can be made that all animals and even plants can consume for fuel.
At the moment the human race has gone in the opposite direction, we make ideal food for cats and dogs that works better with there digestive system, this in turn makes it harder to consume by other animals.
So your military or what ever organization monitors them, will have some kind of Food-X to help with refuge relief efforts.
However for people the ideal survival food would be potato mash, milk and a small amount of butter or margarine. Eating some thing like this for a long time will be unpleasant. Also in real relief efforts grain is used instead, it has a wider variety of uses.
To avoid players saying Food-X isn't realistic you can be vague about it, use some thing like "Made by scientist to help alien refugees, during times of war." for flavor text.
You could also let the player choose between importing from other alien planets for a high prices, or using Food-X but it negatively effects war propaganda.