By definition, organically grown foods are produced without most conventional pesticides, fertilizers made with synthetic ingredients or sewage sludge. Livestock aren't given antibiotics or growth hormones. And organic farmers emphasize renewable resources and conservation of soil and water.
To compare the nutrient density of organically and conventionally grown grapes, researchers would have to have matched pairs of fields, including using the same soil, the same irrigation system, the same level of nitrogen fertilizer and the same stage of ripeness at harvest, acknowledged Charles Benbrook, chief scientist at the Organic Center, a pro-organics research institution.
Last summer, the American Journal of Clinical Nutrition published a comprehensive review concluding that organic and conventional food had comparable nutrient levels.
The study outraged some members of the organic community, who criticized the study for not addressing pesticide residues, a major reason people choose organic. Nor did the study address the effect of farming practices on the environment and personal health.
Maria Rodale, a third-generation advocate for organic farming, urges consumers to look beyond nutrition to the chemicals going into our soil, our food and our bodies. "What we do to our environment, we are also doing to ourselves," said Rodale, chairwoman and chief executive of Rodale Inc., which publishes health and wellness content.
Here's a closer look at some of the factors that may influence your decision whether to buy organic products.
Fruits and vegetables
Farmers using conventional practices treat crops with pesticides that protect them from mold, insects and disease but can leave residues. Organic fruits and vegetables have less pesticide residue and lower nitrate levels than do conventional fruits and vegetables, according to a 1996 scientific summary report by the Institute of Food Technologists.
The bottom line: Pesticide residue poses little risk to most consumers, health experts say. But fetuses and children are more vulnerable to the effects of synthetic chemicals, which can be toxic to the brain and nervous system, said Dr. Philip Landrigan, director of the Children's Environmental Health Center at the Mount Sinai School of Medicine in New York City.
The Environmental Working Group, a public health advocacy organization, recommends buying organically grown peaches, apples, bell peppers, celery, nectarines, strawberries, cherries, kale, lettuce, imported grapes and pears because conventionally grown versions are the most heavily sprayed. Onions, avocados, sweet corn and pineapples have some of the lowest levels of pesticides.
As for nutrition, one French study found that, in some cases, organic plant products have more minerals such as iron and magnesium and more antioxidant polyphenols. But although mounting evidence suggests that soil rich in organic matter produces more nutritious food, "we are never going to be able to say organic is always more nutrient dense; that's going beyond the science," said Benbrook of the Organic Center.
Dairy and meat
Organic dairy and meat products come from animals not treated with antibiotics or genetically engineered bovine growth hormones, which are used to stop the spread of disease and to boost milk production. Past rules on "access to pasture" were vague and didn't require that the animals actually venture into it. But a new regulation requires that animals graze for a minimum of 120 days. In addition, 30% of their dietary needs must come from pasture.
The bottom line: The dairy cow's diet is key. Organic milk has more vitamins, antioxidants, omega-3 fatty acids and conjugated linoleic acid because the cows eat high levels of fresh grass, clover pasture and grass clover silage. Research published in the British Journal of Nutrition found organic milk can improve the quality of breast milk and may protect young children against asthma and eczema.
Though the FDA says milk from cows treated with bovine growth hormone is safe and indistinguishable from other milk, consumers are spooked. Dean Foods, the nation's largest dairy producer, no longer sells milk from those cows, and Kroger (which owns Ralphs), Wal-Mart, Costco, Starbucks, Dannon, Yoplait and several other companies have pledged not to use it.
As with dairy, organic meat has higher levels of omega-3s because of the higher forage content in the animals' diet. It also has lower fat overall than that from animals fed a high-corn diet, said Benbrook. Eating organic dairy or meat also can help with another issue: The use of antibiotics on farms has contributed to an increase in antibiotic-resistant genes in bacteria, say health and agriculture experts.
"Pushing animals to grow really fast has a cascade of effects on the environment and the health of the animal," said Benbrook. "We need to back off the accelerator and focus on the health of the plant, the health of the animal, as well as the nutrient composition of the food."