Ezra Klein said:

Animals also need land. Even if they're penned up in industrial agriculture settings. And it turns out they need a lot more of it than do most crops. The following graph (which comes from this pdf) tracks usable protein yield per acre for a host of foods. Meat doesn't fare well:

I live in Iowa, perhaps the greatest corn-growing entity in the world. Fully one-half the trillions of bushels of corn grown here goes to feeding livestock. You are absolutely correct.

PS: Cattle, by nature, eat grass. But they gain weight much more slowly, and their meat has much less fat. Industrial agriculture makes money turning them over fast, and that's where corn comes in.

The corn grown here is almost inedible. Bred to maximize the endosperm (the big part of the grain, where the sugar is) and minimize the germ (the small part, where the protein is), it is designed to do one thing: make mammals fat fast.

I did not know that. Thanks for the lowdown, masbury.