A TYPICAL SUPERMARKET sells 30,000 to 40,000 products, and each of them puts the environmentally conscious shopper to the test. Organic or conventional? Local or distant? Bulk or packaged? It's not made any simpler by the fact that the finest minds in marketing are trying to sweet-talk you into buying their wares. With all the competing health, nutrition, and environmental claims, you may feel like you need a personal consultant pushing the cart along with you.

Meet Marion Nestle. A professor of food studies, nutrition, and public health at New York University, she's the author of Food Politics (2002), Safe Food (2003), and, most recently, What to Eat: An Aisle-by-Aisle Guide to Savvy Food Choices and Good Eating (North Point Press, 2006). This summer, Nestle helped Sierra decode a midsize Safeway in Berkeley, California.

Here we are inside the sliding doors. Is this a typical supermarket layout?
This is absolutely standard. Fresh foods are on the perimeter of the store; the milk is always in the back. That makes it easier to stock, but to get it you have to walk through the center aisles, which are where most of the impulse buys are. The store is organized for you to buy impulsively.

The produce department is the first thing we see. Why start with produce?
Every single aspect of the supermarket is researched, and the research is unambiguous: That's what brings shoppers into the store. Produce or flowers are pretty much always near the door or to the immediate right or left. The more beautiful the produce section is, the more people are enticed in. And look at all these bins with gorgeous asparagus, apples, and strawberries, all beautifully arranged. Organic on one side and "garden produce" on the other. Michael Pollan has a name for this in his new book, The Omnivore's Dilemma. He calls it "supermarket pastoral."

The first thing we come to is asparagus: 99 cents a pound, pretty nice, they look beautiful. I assume they're local, but without country-of-origin labeling, how would we know? Congress passed a law requiring country labeling by 2004, but the food industry forced postponement of everything except fish until 2008, claiming it would cost too much. You would think that everyone would be proud of buying American, but country labeling would reveal how much of our food is imported.

Why do we care what country our food comes from?
Other than the high price and lack of freshness? Food ecologists call the distance a food travels "food miles." What you see in this store is the product of a global food supply, where goods are brought in from huge distances, which means burning an enormous amount of fossil fuel.

If you want to know where produce comes from, you have to go to Whole Foods; it's the only chain that consistently labels origins. It's part of their shtick, and I think it's a great contribution. But in this store, it's a mystery.

Let's tour the packaged vegetables.
I never buy bagged salads because by the time they get from California to New York, they're a little squeamish-looking. Californians are so lucky. These salads look fresh and undoubtedly are much fresher than we get in New York.

Why salad in a bag?
For convenience. People love it. If you ask people why they don't eat salads or buy salad vegetables, they say it's too much trouble, they have to throw too many leaves away, and it takes too much time to wash and cut. People assume that these are beautifully washed and can be used exactly as is. My advice is to always wash vegetables. There've been several really nasty incidents with contaminated bagged salads making people sick.

Can we assume that any of this produce is local?
You don't really know. It's easier for Safeway to buy it all from the same place. Let's look at these berries from Driscoll's, the big berry producer. Gorgeous! They're from Watsonville, about 90 miles away. Stores in upstate New York sell Driscoll's raspberries from California because the supply is reliable, even when there are terrific raspberries growing ten miles up the road.

Here's the organic section.
And look at what they've got! Safeway has a new organic line, elegantly labeled with a big O. Here are some organic, peeled mini carrots, priced quite favorably. (They aren't really baby carrots, by the way--they're milled from whole carrots.) And this store also has little packages of carrots with SpongeBob SquarePants on the label. Whether SpongeBob makes kids think carrots are cooler or not, I don't know, but this looks to me like direct marketing to kids. Not a good idea.

Let's talk about tomatoes.
The sign on this bin says they're a "great source of cancer-fighting lycopene and vitamins A and C." So now it's not enough to eat tomatoes because they taste good; you've got to eat tomatoes because they've got cancer-fighting lycopene. How well lycopene fights cancer is something scientists will be debating forever. It is said to prevent prostate cancer, so you guys are supposed to be eating them.

Isn't it good for people to know about a product's health effects?
I think it makes people crazy. It's misleading nutritional information, because all tomatoes have lycopene and vitamins A and C. You don't know whether these have any more or less than the others. The deep, dark secret of nutrition in America is that the USDA doesn't have that information either. Getting this information is expensive, and nobody wants to pay the USDA to get it.

We're in the milk section now. It's getting harder and harder to find plain old milk.

Look--fat-free half-and-half! Half what and half what?
Good question. Here's the label: "nonfat milk, milk, corn-syrup solids, artificial color"--yuck!--"sugar," and then assorted junk.

Corn syrup in milk?
It's to make it seem like half-and-half when it is actually creamless. This is a sweetened milk product, just like nearly all yogurts these days. They're just dairy desserts with a health mystique.

Aha! Here's Safeway's organic milk line. Horizon Organic is underneath. Safeway prices its organic milk so it costs less than Horizon's, so people will get used to the Safeway product.

Everyone asks me whether "certified organic" means anything. It sure does. It means the producers follow the rules set by the USDA to the letter and are inspected to make sure they do. Complaints about organics come from two sides--advocates who wish the rules were stronger, free of loopholes, and more sustainable; and big organic producers who work relentlessly to weaken the rules so they can sell organic food more cheaply. The rules are new; it's going to take some time to work out the problems.

Here's something I've never seen before: reduced-fat Milky Way Chocolate Milk. "Tastes just like a Milky Way bar." Is this a good idea? Just what you should be giving your kids for breakfast: liquid chocolate bars!

And here are the breakfast cereals.
The cereal companies are always on the cutting edge of marketing. Notice that the boxes all sport health claims of one kind or another. Cheerios says it can reduce your cholesterol. If you eat this one, you'll lose ten pounds. A miracle! How do you do that? You replace two meals a day with servings of cereal and low-fat milk, you control portion size on your other meal, and you add more physical activity.

That would do it! But haven't cereals become healthier over the years?
Yes, to some extent. They used to have much more sugar than they do now. But they're still what we call in the trade "rapidly absorbable carbohydrates": They don't have much fiber, and they're presweetened, usually with corn syrup. Corn syrup is a lot cheaper than cane or beet sugar because corn is subsidized. The cheaper the sweetener, the more of it shows up in processed foods, the more of it we eat, and the more calories we take in.

My feeling about cereals is: Look for a short ingredient list (other than the vitamins that have to be added), lots of fiber, and little or no added sugar. Even if you add your own sugar, it will still be less than what the companies put in.

It seems the food industry has reacted to health concerns by putting what appears to be health information on packages without actually changing the products.
Health absolutely sells food products. We're now in the section of the store targeted to what marketers call LOHAS: "lifestyles of health and sustainability." Growth in the food industry has been slow for decades, but foods for LOHAS are the fastest-growing segment. Every company wants to get in on this action. That's why Safeway introduced organics, and that's why Wal-Mart's going in.

Organic standards are set by law, but determining whether all the other claims--natural, fair trade, certified this or that--are real or misleading requires an awful lot of research and critical thinking. I had a year with nothing else to do when researching What to Eat. No average consumer could or would want to do this.

Look, Safeway is making organic frozen dinners! The thing that drives me crazy is putting health messages on things that are not so terrific for you. For example, here's an organic macaroni and cheese dinner. Someone looking at that might think that if it's organic, it must be healthy.

Sierra readers might say if it's between this and the nonorganic one, they'll take the organic.
That raises a key philosophical question: Does a small change in a food make that much difference to health? I'm not convinced. It's clearly good to have fewer pesticides in the soil and water--not to mention in your body and your children's bodies--which is why it's good to buy organic. But organic junk food is still junk food.

Let's talk about convenience foods.
It would be nice if everyone were home cooking, but that's unrealistic. Many people don't want to cook, they feel they don't have time, and maybe they don't care so much about taste. The predominant taste in many convenience foods is salt or sugar. But people must like them well enough to buy them because here they are, and they wouldn't stock them if they didn't sell. Many of them come in fancy boxes and plastic packages that have to be thrown out. That's part of the added value to the manufacturers, but not to the environment.

Let's look at whole-wheat breads. This label says "100 percent whole wheat" and sounds promising. Whole-wheat flour is the first ingredient. Water is second--so far so good. Uh-oh: High-fructose corn syrup is third, and look at the additives that come next. This is whole-wheat bread that's been treated with preservatives to keep it soft.

What does the corn syrup do?
You don't like your bread sweet? Sugar disguises the taste of the bitter additives, and I guess they figure that's the only way they can get people to eat whole wheat.

Where does Safeway fit within the supermarket industry?
A supermarket like this is in a terrible position. It's stuck between Wal-Mart at the low end and Whole Foods at the upper end. Whole Foods is booming because people are willing to pay more for their food--although it's now advertising that its prices are no higher than anyone else's. Wal-Mart is the gorilla in the room. Even though food sales are a fraction of its total sales, they're higher than those of any other grocery chain by billions of dollars a year. (See "Lay of the Land." )

How different is Whole Foods from this Safeway?
This particular Safeway has a big push on organics, but it's just starting. Whole Foods is trying really hard but has to source organic foods from all over the world. I saw organic apples from New Zealand in my local store. We don't grow apples in America? It takes tremendous amounts of fossil fuel to get those heavy apples to New York.

Let's look at bottled waters. These are fun. Here's Fiji Water: This has to be the most brilliantly marketed product ever. It really does come from Fiji, where "rainwater filters through volcanic rock over hundreds of years. It's the way nature intended water to be, untouched." Huh? In a plastic bottle?

Then there's Coke's water, which is Dasani. It's tap water that's been filtered and purified. Pepsi's Aquafina is the same.

How did bottled water come to be?
Brilliant marketing, along with a highly successful disinformation campaign about how tap water is not healthy. Yes, there has been a steady deterioration of tap-water quality over the years as industries have been allowed to pollute waterways to their hearts' content, so there's a grain of truth in it. But today people don't even trust decent water supplies. In New York schools, where the water is just fine, kids expect to buy bottled water. I think that's shameful.

Corporations are very smart. Coca-Cola and PepsiCo are in trouble because there's so much competition over soft drinks, and resistance to soft drinks because of the obesity problem. They are happy to sell bottled water. Why not? It costs practically nothing at the tap, and yet look at the prices: $1.29 for bottled water, $1.29 for diet soda, $1.29 for everything.

What about fitness water?
It has vitamins added. If you want vitamins, take a pill. They usually add a little sweetener to cover the yucky taste of the vitamins, and it sells for $1.69. That is one expensive vitamin pill.

Is there anything the food industry hasn't figured out how to add value to?
No, you can add value to anything. There are marketers all over the world who are dreaming up ways to get you to pay more for something that used to be free.

The big environmental issues with water are packaging, and the enormous wastage that comes with that, the distance it travels, and the costs of transportation. I drove partway across the country recently and could not believe how the entire right lane of the interstates is taken up by trucks carrying food. Truck after truck after truck. The amount of fossil fuel that's being consumed to move this stuff from one place to another must be staggering.

Now we're at the fish counter.
Here is one place where the politics of food are as clear as can be. If you want to do something about methylmercury in fish, you have to do something about coal-burning power plants--the source of at least 40 percent of this toxin. I once called one of the big fishing-industry lobbying organizations and asked, "Did you file comments on the latest Bush proposal to postpone restrictions on coal-burning power-plant emissions?" They said, "No." I said, "Why not? Why aren't you in there fighting to have those emissions controlled? It would make the fish healthier, and you would have an easier time selling fish." But they would much rather deny the problem and attack the scientists who say that there's a problem. All they really care about is selling fish now and not at all about the sustainability of fish in the oceans. The shortsightedness of the fish industry is no different from the shortsightedness of any other extraction industry.

Let's check out country-of-origin labeling, which is required on fish. The labels are also supposed to say if they are fresh, frozen, farmed, or wild. Here's Atlantic salmon. "Color added." That tells you it's farmed. Sure enough: "farm-raised from Canada, with feed containing astaxanthin, one of the carotenes found naturally in salmon." Good thing I brought glasses; this has to be six-point type.

The fish counter is the Wild West of the supermarket. You have to know so much about what the fish are, what they eat, where they were caught, and whether they are farmed or wild to know whether they are safe to eat or are endangered species. The big, predatory fish like sharks and sword-fish are loaded with methylmercury and off-limits to children, pregnant women, and women who might become pregnant. Farmed salmon have higher levels of PCBs than wild fish, at least those from some parts of the ocean. And then there are issues of sustainability and how fish are caught. I can't keep it all straight and absolutely depend on fish-advisory cards from the Monterey Bay Aquarium and Environmental Defense.

We're in the freezer aisle now.
Let's count the shelf space for frozen desserts. Let's see ... more than 300 feet of shelf space devoted to ice cream. Add in the frozen cakes and we have 350 linear feet of frozen desserts. And then there are the nonfrozen desserts and all the sugary cereals and yogurts and salad dressings, all increasingly desserty. Dessert has moved into mainstream meals as a normal way of eating. It's no wonder people are gaining weight.

Is the amount of candy and dessert people eat increasing?
Not nearly as much as the candy makers would like it to. They feel there's much room for improvement, particularly the chocolate makers, who are using health in a big way. Chocolate has flavanol antioxidants [naturally occurring chemicals thought by some to prevent diseases], so now they want it to be considered a health food.

How come wine companies haven't gotten into that? Red wine has lots of antioxidants.
Oh, they have and long ago. The Wine Institute has been trying for years to get labels on bottles saying that drinking wine reduces the risk of heart disease. They would love to advertise wine as a health food, but those mean government agencies won't let them.

This all seems pretty complex. You're the one who's supposed to tell us what to eat. What's the bottom line?
Dietary advice isn't all that complicated: Eat less, move more, eat plenty of fruits and vegetables, and don't eat too much junk food. That's really all it takes. Oh, and enjoy your dinner, of course.

Paul Rauber is a senior editor for Sierra.

"Green Cuisine" logo by Greg Mably