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The OTA survey in 2011 found that despite the slow economy, more people were buying organic, at least occasionally.

“It’s clear that with more than three-quarters of U.S. families choosing organic, this has moved way beyond a niche market,” Ms. Bushway said at the time, noting that the trade group’s survey of its members estimated that the U.S. organic industry grew at a rate of nearly 8 percent in 2010 and “is one of the few components of the U.S. economy that continues to add jobs.”

But is organic really more healthy than other foods, Dr. Smith-Spangler and her colleagues wondered.

They reviewed 17 human studies and 223 studies of nutrient and contaminant levels in unprocessed foods, such as fruits, vegetables, grains, milk, eggs, chicken, pork and meat. They compared health, nutritional and safety characteristics or organic and conventional foods.

While there were modest differences in the estimated risks of exposure to pesticide residues or antibiotic-resistant bacteria, evidence “does not suggest marked health benefits from consuming organic versus conventional foods,” they concluded.

Moreover, while eating organic produce reduced the risk of exposure to detectable pesticide residues by 30 percent, “the differences in risk for exceeding maximum allowed limits were small.”