Why can Jen family have junk food only in among the hidden?

In "Among the Hidden" by Margaret Peterson Haddix, the Jen family can only have junk food because they live in a society that strictly controls food distribution and consumption due to overpopulation. As a family with a third child, they must hide their son and adhere to strict regulations to avoid detection. Junk food, being less regulated and often more readily available on the black market, becomes a forbidden treat that symbolizes their rebellion against the oppressive rules of their society. This reflects the themes of scarcity and the desire for normalcy in a controlled environment.