But there are things you can do as individuals, and I’m going to talk to you as individuals, and perhaps during the questions, we can talk about general policy changes that are needed. But what I try to do is: OK, if we can’t count on the scientists to tell us how to eat yet, who can we count on? It’s not me — I’m just a curious writer, really just learning about all this stuff. And I thought long and hard — Well, science is the greatest authority on all matters biological, right? But are there any other authorities?

And I thought historically, as I like to do, and I realized that of course there are other authorities. Before the ascent of science, we relied on culture to help mediate or negotiate our relationships with the natural world and with our own lives. So maybe culture has some wisdom in these questions that we can still take advantage of.

If you go back to the beginning of food, that is a lot of how culture has been viewed. Think back to that first band of primitive humans, who were omnivores, trying everything and discovering that certain things make you sick. How did they negotiate that?

Well, imagine that scene in the state of nature where that group of humans, one picks up a mushroom and eats it, keels over and dies. The others think, “We’ve got to remember this.” (Laughter.) “How can we remember this?” And they say, “Well, we have this language, we have this amazing tool, the animals don’t have this tool. Let’s give it a name, let’s give it a really memorable name.” So somebody says, “I got it, let’s call it the death cap.” No one’s eating a mushroom called death cap.

And that’s kind of the prototype of culture guiding us through our food choice. It’s essentially trial and error, codified in the wisdom of the tribe. So I went back to the rules and I want to leave you with a couple of how culture may guide us in our eating while we wait for science to figure it all out. Because there was a wisdom about foods, and there still is wisdom. It’s in your families, it’s in your great-grandparents or your grandparents, and it’s worth recovering.

I’ll never forget my Mom’s role in this. She is a very vivid contemporary woman and when we were growing up in the 1960s, she got us off butter and onto margarine. Because she had absorbed the public health message, the advertising message, the government’s message to eat less animal fats.

And so she switched us over to margarine, because that was the enlightened thing to do. And the whole time she would say to us, “Someday they’re going to find out that butter is better for you than margarine” (laughter).

Well, she was right. Butter is better for you than margarine. These supposedly unhealthful saturated fats in butter were replaced with what we now know is this demonstrably lethal fat, trans fat. That’s how they kept the vegetable oil rigid at room temperature — they shot it full of hydrogen, creating these trans fats that we now know are really bad and we have that on very good authority.

So why did my mother do that? Well, her cultural wisdom had been undermined by some really lousy science. And we didn’t know it. It seemed like a good idea.

So my rules, which I’ve boiled down in this book to seven words that I’ve put right on the cover of In Defense of Food: Eat food. Not too much. Mostly plants.

So no one has to buy this book (laughter). Just get an index card. But if you think about it, you do need to buy this book (laughter).

So actually I spent 14 pages in this new book defining food, because we’re not eating food, we’re eating a lot of edible food-like substances. So I’ve come up with some rules to help you distinguish between food and food-like substances. For instance: Don’t eat anything your great grandmother wouldn’t have recognized as food.

Just imagine your great-grandmother, rolling down the aisle at the supermarket, she’s with you, she’s at your side, and you get to the aisle that has the Go-gurt portable yogurt tubes (laughter). And she picks up this box and she looks at it, and she pulls one out like a toothpaste tube — “Well, what do you with this? How do you get it into your body?” And then she looks at the ingredients.

And yogurt, yogurt’s a very simple food, it’s one and a half ingredients. Milk and a little bit of bacterial culture are all you need to make yogurt. So what are those 15 other things in Go-gurt? What’s the xanthan gum doing there? What’s carrageenan? What are the red dye No. 40s — all this good stuff?

So that suggests another one: Don’t eat any foods that have more than five ingredients, or have any ingredients a fifth grader can’t pronounce. That’s a pretty good rule of thumb.

So I have a whole bunch of rules to guide you with shopping. Another one is buy all your food from the periphery of the store and stay out of the middle. Every food stores is laid out pretty much the same way. The perishable real foods, in all these stores built in the last 75 years, are on the perimeter. Why is that? Because they’re perishable, they have to be resupplied a lot, so they want to be near the loading dock at the back of the store. Whereas the stuff in the middle never goes bad (laughter).

And that suggests another rule, which is: Don’t eat any food that won’t eventually rot. There’s one exception, there’s one good food that doesn’t rot, and that’s honey. They’ve eaten honey from pharoahs’ tombs that’s been OK. But in general, food should be alive, and therefore it should die.

I have this pair of Twinkies that I bought in 2006 during the book tour for Omnivore’s Dilemma, and when I got home, nobody would take them — I think I made people too self-conscious to want them. So I put it on my bookshelf right near my desk, and every now and then when I’m on the phone, distracted, I’ll just give them a little squeeze(laughter). The Twinkies are as soft and spongy as the day I bought them.

And you have to think, why is that? What does it mean for something to rot? What it means is that the microbes we share this planet with, that we complete with for nutrition, are not interested in those Twinkies (laughter and applause). The microbes leave them alone and probably we should too.

If you have any good cultural rules for eating, I want to put them up on my Web site — please send them to me at michaelpollan.com. I would really appreciate it. There are rules that I came up with for how to tell the food from the non-food, but you also learn when you study nutrition that it’s not just about the food — and it’s definitely not about the nutrients — but it’s also not just about the foods, it’s about the culture that surrounds the foods, it’s about how we eat. It’s about, are we eating alone, are we eating in the car? It’s about the portion size.

And so there’s a whole set of rules a culture has to govern appetites. We will eat too much without some sort of cultural check. We know this. Portion size is one of the great predictors of how much you eat — we have a unit bias. So that when you are fed a supersize portion, you eat 30 percent more.

There was a test at Cornell a few years ago in the dining hall where they where they set up these soup bowls of tomato soup. They set it up with a pipe on the bottoms, so they would refill as you ate. And these students would come in there and eat their soup, and the ones who had the refilling one would eat 30 percent more soup that people who were eating what their bowl told them they should eat, they would finish it to the end.

And they asked them after, what’d you think of the soup? And the ones with the refilling bowls said, “That’s a hearty soup, man” (laughter).

So the size of your plate matters. There’s a rule the Japanese help and many other cultures have this as well, called hara hachi bu, which means eat until you are 80 percent full. Kind of a weird concept. I mean you have to go all the way, and then double back (laughter). But you do that once and then you kind of get it. Stopping before you are really full is a distinctly un-American idea, but many other cultures cultivate it. There’s a German saying, you must tie off a sack before it’s full, and Muhammad actually spoke about this issue, stop eating before you’re full. We’re very manipulated by portion size.

So those are some of the how-tos. And people who look at the “French paradox” — you’ve heard about this, French people eat these supposedly lethal high fats and triple crème cheese and foie gras, washed down with lots of red wine, and how is it they’re healthier than we are — is it the red wine, is it the foie gras? It may be the way they eat. They don’t like to eat alone. They think eating in the car is really disgusting. Meals are social events, they’re not just transactions. So you need to pay attention to the manners of cultures who perhaps have it right.