You are what what you eat eats.

The old saying "you are what you eat" stops one step too soon, and Pollan's twist adds the missing link. Whatever lands on your plate has its own diet, and that diet becomes part of the food you receive. A steer fed mostly corn in a feedlot gives you a different kind of meat from one that grazed on grass, and a person eating that beef is, in a roundabout way, eating the corn too. The quote asks us to see a meal as the end of a long chain rather than a single item.

This fits Pollan's wider view, familiar from his writing on food, that eating is an ecological act connecting us to soil, farms, and industrial systems, and that we should pay attention to how food is produced, not just to nutrients on a label. The older proverb is far more widely known than this wording, so the sentence is best read as his sharpening of it.

In practice, it might mean that when you buy eggs or meat, you occasionally choose ones from animals raised on pasture, or simply ask where your food came from. Even eating a little less meat of unknown origin is a quiet way to take the idea seriously.