An author's purpose is their reason for writing. Purposes can range from narrative (telling a story) to persuasive (convincing the audience of something) to expository (revealing something not widely known and informing the audience about it) to descriptive (focusing on sensory details). In The Omnivore's Dilemma: A Natural History of Four Meals, Michael Pollan's purpose is largely expository, but he also has a persuasive intent to some extent.

Pollan exposes America's “national eating disorder,” claiming that Americans are typically confused about their food choices because there are just so many. He goes on to follow the trail of some of those food choices by writing about four particular meals from three food chains, industrial, organic, and hunter-gatherer. He follows the journey of corn, for instance, from the field, through processing, to the grocery store. He traces the life of a cow. He examines the reality of fast food. He also explores the practices of organic farming and even tries to put together a meal in which he gathers or hunts every bit of it himself. Along the way, Pollan reveals little-known facts about food that will surprise and perhaps horrify most readers, and this, of course, is the whole point. Pollan wants his readers to become more aware of the food they eat.

There is also a persuasive element to Pollan's book. As readers become more aware of their food, they might well wish to change some of their eating habits. While Pollan is not saying that everyone should grow all their own food, he does encourage people to be more conscious of their food choices and the consequences of those choices and to change some of their eating habits to healthier, more sustainable options.