Consumerism
This idea took over the thoughts of characters in Feed so much so that many of them could not think without having some brand come into mind. It takes over the world and leaves in ruin.
Man and the Natural World
In Feed, the environment has been destroyed by the lifestyles of the people. The forest are all but gone and the natural water sources are dry or toxic. It also has influence on how the characters live and look.
Identity
With the constant stream of information and advertisement, the companies controlling the feed also controlled the people. In order to make selling products easier, companies grouped the population into a few different categories of personalities. Because of this the identities of most of the characters are unsubstantial.