How does the author use symbolism in the novel, This Is How You Lose the Time War?

The author uses hunger as a symbol of what humanity has lost in the near future, and a symbol of what brings Red and Blue together. At first, Red is unsure if she can even feel hunger since humans have evolved past the need for food. However, the fact that she still eats food anyway for enjoyment shows that she at least has some notion of the concept, and when she begins to feel more of a longing to be close to Blue, she equates that sensation with hunger.