From APM, American Public Media, and WNYC,

this is Freakonomics Radio on Marketplace.

Here's the host of Marketplace, Kyra's Doll.

Time now for a little Freakonomics Radio.

It's that moment every couple of weeks we talk to Stephen Dubner,

the co-author of the books and the blog of the same name.

It is the hidden side of everything Dubner, how are you, man?

Hi, I'm great. Thank you.

Nice to talk to you. You like riddles, don't you, guy?

I do.

All right, let me try something out on you then.

A listener of ours, a fellow named Ralph Thomas,

recently asked us to weigh in on what he calls, quote,

the cheapest, most nutritious, and bountiful food

that has ever existed in history.

He says it's got 390 calories, 23 grams of protein,

substantial portions of calcium iron, and it costs only a buck or two.

So Kyra's Doll, let me ask you this.

What food is Ralph talking about?

It's got to be like tofu or soy or some kind of thing, right?

God, you're smart.

Oh, but you're wrong, but you're wrong also.

...