What is the theme in The Omnivore's Dilemma: A Natural History of Four Meals by Michael Pollan?

The primary theme of the novel is the Omnivore Dilemma. As author Pollan describes it, the Omnivore Dilemma was originally discussed by writers such as Rousseau and Brillat-Savarin, but the actual term was coined by research psychologist Paul Rozin, in his 1976 paper titled, "The Selection of Foods by Rats, Humans, and Other Animals". The dilemma, as put by Rozin, is that omnivores have a vast choice when eating. Specialized animals, such as the koala, know only to eat one single food because that is all its body is designed to eat.