Once upon a time, organic food was available only at health food stores, marketed to "tree-hugging" consumers willing to pay extra for "natural," environmentally friendly foods. Today, organic foods are undeniably mainstream. Not only can they be found at most every neighborhood grocer, but even giants like Wal-Mart are getting into the act.

People who buy organic are seeking assurance that food production is gentle to the earth, and/or looking for safer, purer, more natural foods. But are organic foods really worth the added expense?

"If you can afford them, buy them," recommends New York University professor Marion Nestle, PhD, MPH. "It really is a personal choice but how can anyone think substances, such as pesticides, capable of killing insects, can be good for you?"

But American Dietetic Association spokeswoman Keecha Harris, DrPH, says, "There is no evidence that organic foods are superior over traditional foods."

Food does not have to be organic to be safe and environmentally friendly, she says. She recommends focusing on eating food grown close to where you live. She notes that some organic foods come from multinational companies and have been trucked across the country.

"They may be organic, but the … environmental footprint includes lots of petrochemicals used in transportation, whereas if you buy produce from your local farmers market, it may not be organic but it is farm-fresh and less impactful on the environment," says Harris

One thing the experts agree on: Regardless of whether you choose locally grown, organic, or conventional foods, the important thing is to eat plenty of fruits and vegetables. The health benefits of such a diet far outweigh any potential risks from pesticide exposure.

The Price of Buying Organic Food Just how much more expensive is it to go organic? You can expect to pay 50%-100% more for organic foods. That's because, in general, it is more labor-intensive, and without the help of pesticides, the yield is not always as favorable.

To maximize your organic food dollar, the Environmental Working Group, a nonprofit organization based in Washington, D.C., recommends going organic on the "dirty dozen" -- types of produce that are most susceptible to pesticide residue: Peaches Apples Sweet bell peppers Celery Nectarines Strawberries Cherries Pears Grapes (imported) Spinach Lettuce Potatoes

And which organic produce is probably not worth the added expense? The group lists these 12 items as having the least pesticide residues: Papayas Broccoli Cabbage Bananas Kiwifruit Sweet peas (frozen) Asparagus Mangoes Pineapple Sweet corn (frozen) Avocados Onions

You can help keep costs down by shopping for sale items, comparing prices, buying locally grown products either at farmers' markets or via a co-op. The sale of organic foods in large grocery store chains is also likely to help keep prices down in the long run.

Reduce Pesticide Residues Whether or not you buy organic, you can do your part to reduce pesticide residues on foods with the following tips: Wash and scrub produce under streaming water to remove dirt, bacteria and surface pesticide residues, even produce with inedible skins such as cantaloupe. Do not use soap Remove the peel from fruits and vegetables. Remove the outer leaves of leafy vegetables. Trim visible fat and skin from meat and poultry because pesticide residues can collect in fat. Eat a variety of foods from different sources. Join a co-op farm that supports community agriculture.