The Omnivore's Dilemma is an investigation into the food production chain that leads the author to the belief that local, sustainable food sources are best for everyone.

Michael Pollan posits that humans have a multitude of food choices and yet have little information about where that food comes from. He goes on to say that humans would be better off if they found out more about their food supply chain and chose options that benefited both their health and the health of the planet. For example, it takes a great deal of fossil fuel calories to ship one pound of lettuce with 80 food calories. 

To make his point, Pollan tracks the life of a calf from its beginnings to its end, when it's killed for food. He points out how much corn the cow is fed.

Next, he discusses how organic food is unsustainable and in many ways not better for the planet. He contrasts farms of different sizes and shows the various effects their practices have on the planet. 

Finally, Pollan goes into the woods and creates a meal for himself from ingredients he obtains. He hunts, gathers, and grows ingredients before cooking an entire meal.

At the end, he admits that there is no single approach that will work for everyone -- but that simply having more information about where food comes from would be beneficial and help people make better choices.

Pollan's thesis is that omnivores struggle with the proverbial question of what to eat for dinner because they are faced with a mind-numbing number of choices. Unlike the koala, who feeds on eucalyptus leaves because it is in his or her genetic code, a human has a wide variety of choices. In our choices, we are guided by memory and information (such as our knowledge about what is poisonous and what is nutritious), as well as by our taste buds. In fact, some scientists believe our large brains evolved to help us handle the dilemma of what to eat. While our choices can help us eat food that is pleasurable, our wide variety of choices can also incur stress. As a result, we tend to divide food into good and evil. We are prone to developing eating disorders in which we see food as calories rather than as enjoyment and sustenance. Pollan also believes our place in the food chain determines a great deal about us. This includes the shaping of our memory and powers of observation, as well as the fostering of our dependence on food scientists and marketers to figure out what to eat.

Pollan's main thesis in this book is that we in the United States need to adopt a lifestyle in which we get our food from the "pastoral" food chain rather than from the industrial one.

Pollan argues that we get the vast majority of our food (even the food that is sold as "organic") from an industrial food chain.  He says that this food chain is bad for the environment, bad for the animals that are raised in it, and bad for the quality of the food that it produces.  Instead, he says, we should rely on the pastoral food chain.  He believes that we should be eating food that is grown locally and in a more old-fashioned and sustainable way.  This food would taste better and the way that it is raised would be better for the environment and for the animals that we eat as well.