Does an organic strawberry contain more vitamin C than a conventional one?
Maybe -- or maybe not.
Stanford University scientists have weighed in on the "maybe not" side of the debate after an extensive examination of four decades of research comparing organic and conventional foods.
They concluded that fruits and vegetables labeled organic were, on average, no more nutritious than their conventional counterparts, which tend to be far less expensive. Nor were they any less likely to be contaminated by dangerous bacteria like E. coli.
The researchers also found no obvious health advantages to eating organic meats.
Conventional fruits and vegetables did have more pesticide residue, but the
"When we began this project, we thought that there would likely be some findings that would support the superiority of organics over conventional food," said Dr. Dena Bravata, a senior affiliate with Stanford's Center for Health Policy and the senior author of the paper, which appears in Tuesday's issue of the Annals of Internal Medicine. "I think we were definitely surprised."
The conclusions will almost certainly fuel the debate over whether organic foods are a smart choice for healthier living or a
The findings seem unlikely to sway many fans of organic food. Advocates for organic farming said the Stanford researchers failed to appreciate the differences they did find between the two types of food -- differences that validated the reasons people usually cite for buying organic. Organic produce, as expected, was much less likely to retain traces of pesticides. Organic chicken and pork were less likely to be contaminated by antibiotic-resistant bacteria.
"Those are the big motivators for the organic consumer," said Christine Bushway, executive director of the trade association.
The study also found that organic milk contained more omega-3 fatty acids, which are considered beneficial for the heart.
"We feel organic food is living up to its promise," said Sonya Lunder, a senior analyst with the Environmental Working Group, which publishes lists highlighting the fruits and vegetables with the lowest and highest amounts of pesticide residues.
The Stanford researchers said that by providing an objective review of the current science of organic foods, their goal was to allow people to make informed choices.
In the study -- known as a meta-analysis, in which previous findings are aggregated but no new laboratory work is conducted -- researchers combined data from 237 studies, examining a wide variety of fruits, vegetables and meats. For four years, they performed statistical analyses looking for signs of health benefits from adding organic foods to the diet.
The researchers did not use any outside financing for their research.
"I really wanted us to have no perception of bias," Bravata said.
One finding of the study was that organic produce, overall, contained higher levels of phosphorus than conventional produce. But because almost everyone gets adequate phosphorus from a wide variety of foods, they said, the higher levels in the organic produce is unlikely to confer any health benefit.
The organic produce also contained more compounds known as phenols, believed to help prevent cancer, than conventional produce. While the difference was statistically significant, the size of the difference varied widely from study to study, and the data was based on the testing of small numbers of samples.
Other variables, like ripeness, had a greater influence on nutrient content. Thus, a lush peach grown with the use of pesticides could easily contain more vitamins than an unripe organic one.
The study's conclusions about pesticides did seem likely to please organic food customers. Overall, the Stanford researchers concluded that 38 percent of conventional produce tested in the studies contained detectable residues, compared with 7 percent for the organic produce. (Even produce grown organically can be tainted by pesticides wafting over from a neighboring field or during processing.) They also noted a couple of studies that showed that children who ate organic produce had fewer pesticide fragments in their urine.
The pesticide factor
Bravata agreed that people purchased organic food for a variety of reasons -- concerns about the effects of pesticides on young children, the environmental impact of large-scale conventional farming and the potential public health threat if antibiotic-resistant bacterial genes jumped to human pathogens.
"Those are perfectly valid," she said.
The analysis also did not take factors like taste into account.
But if the choice were based mainly on the hope that organic foods would provide more nutrients, "I would say there is not robust evidence to choose one or the other," she said.
The argument that organic produce is more nutritious "has never been a major driver" in why people choose to pay more, said Lunder, the Environmental Working Group analyst.
Rather, the motivation is to reduce exposure to pesticides, especially for pregnant women and their young children. Organic food advocates point to three studies published last year that identified pregnant women exposed to higher amounts of pesticides known as organophosphates, then followed their children for years. In elementary school, those children had, on average, IQs several points lower than those of their peers.