How would you say "I can't eat spicy food"?
Ich kann kein scharfes Essen essen.
It sounds strange to put two "Essen"s together. Or is it okay? What would be other ways?
Essen essen is perfectly correct. However, I'd translate the can't with darf nicht:
Ich darf nichts Scharfes essen.
Ich vertrage nicht is a little bit different to Ich darf nicht:
Ich vertrage nicht means my body has a bad reaction to spicy food.
Ich darf nicht means I am not allowed to eat spicy food.
Both are possible translations - depending on the writer's intentions.