the organic buying guide.

So, here's a pretty complete answer to the question we've been pushing quite a bit: [Thanks to Martha Stewart: Body and Soul and Lindsey's tip..]

What are you really getting when you pay a little extra for organic? It depends on the food. Here's an expert list of what to buy organic -- and when.

Fruits and Vegetables
Why Buy Organic? When you eat conventional produce, pesticides and chemicals tend to show up in your body. The long-term health effects are unclear, but why risk it? The nonprofit Environmental Working Group studied 43 fruits and vegetables and ranked them according to contamination. Choose organic versions of the 12 worst offenders and you'll reduce your exposure by almost 90 percent: peaches, apples, bell peppers, celery, nectarines, strawberries, cherries, pears, grapes (imported), spinach, lettuce, potatoes.
Did You Know? A diet containing the 12 most contaminated fruits and vegetables exposes a person to an average of 15 pesticides a day.
Peanuts, Soybeans, and Corn
Why Buy Organic? Peanuts rank among the top 10 foods contaminated with persistent organic pollutants, says the Pesticide Action Network. These chemicals linger in the environment for years and can also build up in the body's fatty tissues. As for soybeans, 85 percent of the 2004 crop was genetically modified (GM). Experts warn against buying GM foods since their effects haven't been adequately studied -- on us or the earth. The same warning goes for corn: Nearly half of all corn planted in America in 2004 was GM.
Did You Know? Americans eat about 2.4 billion pounds of peanuts every year -- about half as peanut butter. From 2000 to 2005, more than 2,100 new foods containing soy hit the U.S. market.
Beef
Why Buy Organic? To enhance growth, conventional farmers often give their cows hormones. The FDA says they're safe, but the European Union disagrees -- and has banned their use. Farmers also give cows antibiotics even when they're not sick, contributing to antibiotic resistance. Cows excrete antibiotics and hormones into the environment, too, potentially harming local ecosystems. Finally, the "food" conventional cows eat (like manure) would make your stomach turn. Organically raised cows eat organic feed and grass.Did You Know? In 2004, consumers spent more than $70 billion on beef. In 2005, sales of organic beef totaled nearly $49 million, according to the OTA.
Dairy
Why Buy Organic? The red flag here is recombinant bovine growth hormone (rBGH), a synthetic drug given to cows to increase milk production. Milk from these cows contains higher levels of a natural growth factor called IGF-1. Some experts link excess levels of it in humans to breast and prostate cancers. Although the FDA says it's safe, the European Union has banned the drug. Use of rBGH also increases infections in cows, prompting farmers to administer even more antibiotics.Did You Know? Large farms with 500 or more milk cows represented less than 4 percent of all dairy farms in 2004 but produced nearly half of America's milk.
Pork, Poultry, and Eggs
Why Buy Organic? Farmers use antibiotics on these animals in the same preventive way as with cattle, again contributing to the rise of resistant bacteria and potentially harming local ecosystems. And, like cattle, conventional hogs and poultry eat a range of stomach-turning "foods." In a 2006 study by the Institute for Agriculture and Trade Policy (IATP) of supermarket chicken products, more than half of the samples tested positive for arsenic. One of the IATP's recommendations? Buy organic.Did You Know? Healthy U.S. hogs and poultry ingest about 20 million pounds of antibiotics annually; in comparison, 3 million pounds treat sick people.
Chocolate and Coffee
Why Buy Organic? Both crops naturally grow in the shade. But to meet increasing demand, farmers favor sun-loving varieties, resulting in clear-cutting and heavy pesticide use. Cacao, which is used to make chocolate, is one of the world's most heavily sprayed crops, according to the United Kingdom's Soil Association. The Commission for Environmental Cooperation tells us that if half of North America's 15 million college students chose organic, shade-grown coffee, they would prevent 3,885 tons of chemical fertilizers and 660 tons of pesticides from poisoning the earth.Did You Know? The organic standard doesn't cover fair trade. To ensure just compensation for farmers, look for both the Fair Trade Certified label and organic seal on chocolate and coffee.

Text by Mary Carmichael; photography by Jonathan Kantor. Mary Carmichael is a contributing writer at Newsweek.