Once confined solely to health food stores, farmer's markets and food co-ops, organic food has gone mainstream: In 2000, more than half of the $7.8 billion of organic food purchased in the United States was bought in conventional supermarkets, according to the Economic Research Service of the U.S. Department of Agriculture (USDA).

There's wide agreement that organic food has fewer pesticides than conventionally grown fare. And there are certainly environmental and even ideological arguments to support organic agriculture. But what about nutrition? Is organic food better for you? Does eating it reduce the risk of disease and death?

No studies have systematically compared organic food regimens against conventional fare to examine either short-term or long-term health. The research is simply too expensive, time-consuming and difficult to do.

But a few studies have found that some organic foods may have an edge in some nutrients, mostly vitamin C and other antioxidants. Last year, University of California researchers in Davis reported that organic strawberries, marionberries and corn beat out the same varieties grown conventionally or with sustainable agricultural practices on vitamin C and on compounds called phenols, which are health-promoting phytonutrients.

So is there a health advantage to eating organic?

"We can't say one way or another," said Joseph Spence, director of the USDA's Beltsville Nutrition Center and the department's acting deputy administrator for nutrition, food safety and quality. "We haven't seen benefits demonstrated [from organic food] and we have looked. . . . Despite all the claims that have been made, it's really difficult to find any studies that show different nutritional content of organically grown foods."

Nor is there any definitive evidence to suggest that eating organic food, which usually carries less chemical residue than conventional fare, is directly linked to a lower risk of cancer, heart disease or other common ailments. "But if you want to pick a set of chemicals to avoid, pesticides would be at the top of the list," said Richard Wiles, senior vice president of the Environmental Working Group, a consumer group and advocate for organic food. "What we're talking about is a pretty significant reduction in exposure to pesticides which are designed to be toxic. . . . When you eat organic food, you're getting food without added chemical pesticides, and the more we look at them, the more hazardous they seem to be, particularly for infants and children."

Both the American Chemical Society and the Organic Center for Education and Promotion have scientists looking at ways to investigate potential differences in organic vs. conventional food. Until they sort out the questions, here's what you need to know when considering the choice of organic vs. conventional food:

Organic doesn't mean pesticide-free. It simply refers to an "agricultural production system that maintains and improves the soil and agricultural conditions," notes Cathy Greene, a USDA economist. "It also fosters cycling of resources, promotes ecological balance and conserves biodiversity." By definition, organic food can't have added pesticides, but it may contain residues of pesticides from the soil where conventional crops have been grown in the past. Even so, organic pesticide levels are limited to 5 percent or less of that allowed in conventional crops by the Environmental Protection Agency.

Aim for variety in all foods, including organic. It's the best way both to increase intake of vitamins, minerals and other phytonutrients and to reduce the risk of potentially harmful substances, from man-made pesticides to naturally occurring mycotoxins. Plus, the studies that underscore health benefits from eating more fruit and vegetables have almost entirely been done with conventional -- not organic -- food. "We know that it is important to eat fresh fruit and vegetables and that the value of eating those fruits and vegetables, whether conventionally grown or organic, is very strong," said Katherine DiMatteo, executive director of the Organic Trade Association. "But there are certain vulnerable populations, like children, who may be affected for the long term, because of the pesticide residues that are on conventionally grown fruit and vegetables."

Go for less than perfect. Most people choose plump, blemish-free produce. But it turns out that stress prompts plants to protect themselves by producing more phytonutrients, the very substances that may also have beneficial effects for human health. "The reality is that the beat-up-looking ones may be the richer ones in phytonutrients," Spence said.

Find balance. Even the most ardent supporters of organic food acknowledge that it's not always available and may be too pricey for some. Plus there are trade-offs, notes Nancy Creamer, director of North Carolina State University's Center for Environmental Farming Systems. Is it better for the environment to buy organic raspberries that have been flown in from California or to purchase berries from a local farmer who grows conventionally? "It's not an easy question to answer," said Creamer, who buys both types for her family.

Read the fine print. Just because it's organic doesn't mean it's nutritious. Example: the organic, chocolate-covered, frozen soy dessert bars cited by the Nutrition Action letter of the Center for Science in the Public Interest (CSPI). The bars, whose ingredients include organic coconut oil, contain a third of a day's worth of saturated fat. "Just because foods are organically grown, they still could be loaded with organic fat and organic sugar, and they still could be contaminated with dangerous bacteria," noted CSPI director Michael Jacobson when organic certification began being implemented in 2002.

Prepare to pay more. A 2000-2001 survey of wholesale market prices in Boston found that buyers spent 30 percent more for organic broccoli compared with conventionally grown; 25 percent more for organic carrots and 10 percent more for organic mesclun lettuce. Organic foods tend may have a shorter shelf life than conventionally grown food, which is often bred to be picked green and then slowly ripen during shipping and sales.

Free-range doesn't mean organic. When it comes to livestock foodstuffs -- meat, dairy, eggs and poultry -- there's no official definition of "free-range." But producers of organic meat, dairy and poultry items are required to use 100 percent organically grown feed or pasture land and are prohibited from using antibiotics and growth hormones. By comparison, products labeled simply "natural" or "free-range" don't have to meet those standards.

Grow your own. No back yard or time to till? Then practice urban "farming" in large pots on your balcony or deck. They're great for small crops of lettuce or tomatoes.

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