Adding fuel to the debates over the merits of organic food, a comprehensive review of earlier studies found substantially higher levels of antioxidants and lower levels of pesticides in organic fruits, vegetables and grains compared with conventionally grown produce.
“It shows very clearly how you grow your food has an impact,” said Carlo Leifert, a professor of ecological agriculture at Newcastle University in England, who led the research. “If you buy organic fruits and vegetables, you can be sure you have, on average, a higher amount of antioxidants at the same calorie level.”
However, the full findings, to be published this week in the British Journal of Nutrition, stop short of claiming that eating organic produce will lead to better health. “We are not making health claims based on this study, because we can’t,” Leifert said.
Still, the authors — including a Washington State University professor — note other studies have suggested some antioxidants have been linked to a lower risk of cancer and other diseases.
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The conclusions in the new report run counter to those of a similar analysis published two years ago by Stanford University scientists, who found few differences in the nutritional content of organic and conventionally grown foods. Those scientists said the small differences that did exist were unlikely to influence the health of the people who chose to buy organic foods.
The Stanford study, like the new study, did find pesticide residues were several times higher on conventionally grown fruits and vegetables, but played down the significance, because even the higher levels were largely below safety limits.
Organic farming, by and large, eliminates the use of conventional chemical fertilizers and pesticides. Those practices offer benefits such as healthier soils but produce less bountiful harvests. The Organic Trade Association, an industry organization, estimated organic-food sales last year in the United States at $32.3 billion, or just over 4 percent of the total market.
Many naysayers regard organic as a marketing ploy to charge higher prices.
“The other argument would be, if you just eat a little bit more fruits and vegetables, you’re going to get more nutrients,” said Alan Dangour, a researcher at the London School of Hygiene and Tropical Medicine. Dangour led a review published in 2009 that found no significant nutritional differences between conventional and organic foods.
In the new study, an international team of scientists did not conduct any laboratory or field work of their own. Instead, they compiled a database from 343 previously published studies and performed a statistical procedure known as a meta-analysis, which attempts to ferret robust bits of information from studies of varying designs and quality.
Overall, organic crops contained 17 percent more antioxidants than conventionally grown crops, the new study found. For some classes of antioxidants, the difference was larger. A group of compounds known as flavanones, for example, was 69 percent higher in the organic produce.
Charles Benbrook, a professor at Washington State University and another author of the paper, said the new analysis improved on earlier reviews, in part because it incorporated recent new studies.
The findings fit with the expectation that without pesticides, plants would produce more antioxidants, many of which serve as defenses against pests and disease.
The study also found that organically produced foods, particularly grains, contain lower levels of cadmium, a toxic metal that sometimes contaminates conventional fertilizers. Benbrook said the researchers were surprised by that finding; there was no difference in other toxic metals such as mercury and lead.
The study cost $429,000, which came from the European Union and the Sheepdrove Trust, a British charity that supports organic-farming research. The scientists said the money came with no strings, and their research passed scientific peer review for publication.