July 30, 2009 -- Organically grown food is no more nutritious than conventionally grown food when it comes to the amount of certain important nutrients, according to a new review of published studies.
"We wanted to answer the question, 'Is there any evidence that organic food is nutritionally superior to conventionally grown food?'" says the study's lead author, Alan D. Dangour, PhD, a public health nutritionist at the London School of Hygiene & Tropical Medicine. "The answer is no. Organic food is not nutritionally superior to conventional food."
The conclusions of the review, published in the American Journal of Clinical Nutrition, drew strong disagreement from U.S.-based food researchers.
The global market for organic foods is estimated to be about $48 billion annually, according to the London researchers. Organic foods are produced under standards that control the use of chemicals in crop production and medicine in animal production, among other regulations.
Organic vs. Conventional Foods: Review
Dangour and his colleagues searched for studies comparing organic and conventionally grown food from January 1958 to February 2008.
They found 55 studies of satisfactory quality to include in their review and evaluated several nutrient categories, including:
• Phenolic compounds (also called polyphenols)
• Total soluble solids
• Acidity content
They found that conventionally produced crops had a higher content of nitrogen, while organically produced crops had higher phosphorous and acidity content. No difference was detected for the other crop nutrient categories analyzed. When they looked only at animal-source foods, the researchers found no difference in nutrient content.
The review, funded by the U.K. Food Standards Agency, didn't look at differences in pesticide residues between the two growing methods.
Organic vs. Conventional: Other Views
Officials from the U.S. organic food industry, not surprisingly, took strong exception to the review, as did some other experts.
''Our stand is it's beyond scientific doubt that that organic foods are higher in vitamins and important trace minerals and there are far fewer toxic residues in them," says Ronnie Cummins, national director of the Organ Consumers' Association. "And that's the reason that millions of American consumers are paying a premium price for organic production."
One problem with the new review is the use of older studies, some done in 1958, says Michael Hansen, PhD, a senior scientist at Consumers Union and a food safety expert. "Newer studies have clearly shown significant differences between organic and nonorganic when it comes to nutrient content," he tells WebMD.
''Most of the studies published before 1980 are flawed for a number of reasons,'' he says, including flawed methodology.
Nutrients as a whole in the food supply are declining, Hansen says, citing another reason not to lump 1958 studies with more current ones.
But Dangour responds that criticism is off base, as the comparisons of organic versus conventionally grown food were done within individual studies. And, he says, "the majority of studies [reviewed] were published since 2000."
Charles Benbrook, PhD, chief scientist for The Organic Center, a Boulder-based industry group, says his center's research has produced different conclusions. "The more contemporary studies and higher quality ones do clearly support nutritional benefit for organically grown foods compared to conventionally grown foods," he says.
He criticizes what he calls a lack of focus on polyphenols and antioxidants, which he says are about 25% higher in organically grown foods. The London team "downplays" the differences they did find between the foods, he says.