GWEN IFILL:Finally tonight: how technology has changed the foods we eat.

Hari Sreenivasan has our book conversation.

HARI SREENIVASAN:Human eating habits have changed more in the past century than in the previous 10,000 years. In the U.S., Americans are consuming double the fat, 3.5 times more sodium, 60 percent more sugar and infinitely more corn and soybeans than in the year 1909.

One culprit, processed food. About 70 percent of our calories come from them. It's a topic of a new book by former New York Times business reporter Melanie Warner called "Pandora's Lunchbox: How Processed Food Took Over the American Meal."

Melanie Warner joins me now. Thanks for being with us.

MELANIE WARNER, "Pandora's Lunchbox: How Processed Food Took Over the American Meal": Yes. Thank you for having me.

HARI SREENIVASAN:So, first of all, define processed food, just so we're all on the same page.

MELANIE WARNER:Yes, it's a term that is thrown around a lot these days.

I like to think of it as a processed food is something that you could not make at home in your own home kitchen with those same ingredients. So, you could apply to packaged food. You can apply to fast food. And I think that's a good—good benchmark.

HARI SREENIVASAN:So, you did this kind of interesting experiment. You wanted to see how processed food sort of devolved or what their shelf life was. And what did you do? Explain this to the audience.

MELANIE WARNER:Yes. It was something that I came upon a number of years ago where I started wondering about expiration dates on packages, food in the supermarket.

Pretty much every package has an expiration date on it somewhere. And I wondered, what would happen after this date came and went? Would the food good bad? Would it start smelling? So, I just started collecting some food and keeping it in my—then it was an apartment and to see what happened. And, eventually, I would open it and everything would be fine. Nothing—there would no mold, no bad smell.

So, over time, I just collected. I became curious, well, what would happen if I tested other kinds of foods? And I got—I started collecting fast food and all kinds of other supermarket products, frozen meals, kid’s meals, Pop Tarts. You name it. My office was filled with the stuff.

HARI SREENIVASAN:So, what should have been a very smelly area wasn't smelly.

MELANIE WARNER:It wasn't very smelly at all.

It was in my office and I was still able to work there. There were a few exceptions, but for the most part, none of it molded, started smelling bad or otherwise decomposed.

HARI SREENIVASAN:OK. And you say in your book that while science and technology has made it easier to process foods, our bodies have not evolved at the same pace. Explain that.

MELANIE WARNER:Yes. That's correct.

We have had an enormous amount of technological innovation in the last 100 years. Technology has merged with—with food production in a way that few of us, I think, realize, but the way our bodies process food is stuck somewhere in the Stone Age, when we were eating very different foods, obviously.

This causes enormous problems, because the foods that we're eating, our bodies are really not designed to handle. And it causes all kinds of health problems.

HARI SREENIVASAN:So, is there some sort of scientific data that says we don't have the enzymes or what is happening in our bodies when this processed food hits it?

MELANIE WARNER:Well, you can look at different things; you can look at different ingredients.

Certainly, if you take sugar, the effect that sugar has on our bodies is—can be somewhat disastrous if it's overconsumed. Metabolically, it causes our blood sugar to spike. And you a lot hear about people getting insulin-resistant. And it just—it messes up the whole blood sugar dynamic when we consume too much sugar.

And then you can talk different about things like fats and vegetable oils. And we're overconsuming those. And that's having problems for our arteries and our vascular system and our heart.

HARI SREENIVASAN:OK. Some of these preservatives, the food industry is going to come back and say in fact it's because of the preservatives, it's because of the fortifying things with vitamins and minerals that we are maybe even going to have a chance at feeding the seven billion people that are on the planet. So, we kind of need this science, we need this to feed everybody.

MELANIE WARNER:Yes. I would argue that that is not the only way we can feed people and that's not the best way to feed people.

You look at, do we really want the rest of the world adopting our diet of eating processed food, where we're eating 70 percent processed food? And our health statistics are abysmal. We're supposed to be a great country, and we're 37th in life expectancy globally around the world.

So, I just don't think that that is a solution for feeding the rest of the world.

HARI SREENIVASAN:So, after having written this book and knowing this much about processed foods, what is your diet like? What are you cutting out? What are you including?

MELANIE WARNER:I think it's—I want to stress that I'm not arguing for a world without any processed food, zero processed food.

I think it's a matter of rebalancing our diet so that instead of 70 percent of our food coming from highly processed products, maybe it's something like 30 percent or 20 percent, or whatever is right for an individual. So, that's the way I try and eat. I do eat processed foods. I do serve them to my kids. I'm a working mom.

So, I try and have a balance. And when I do serve processed foods or eat processed foods, I try and seek out the best choices, the ones that don't have as many ingredients, that don't have artificial ingredients, so the less processed of the processed choices.

HARI SREENIVASAN:OK, examples would be?

MELANIE WARNER:Like, for instance, I don't buy a boxed mac and cheese anymore for the kids, because I thought, why I do want to be feeding them powdered cheese or liquid cheese, instead of the real thing? To make it at home is relatively easily. So, I have become just a little bit more skeptical and discriminating.

HARI SREENIVASAN:All right, the book is called "Pandora's Lunchbox."

Melanie Warner, thanks so much for your time.

MELANIE WARNER:Yes. Thank you.