The study looked at fruits, vegetables, eggs, grains, dairy, poultry and… (Sergio Dionisio / Bloomberg )
Many people shell out extra money for organic food in the belief that it's safer and more nutritious. What are the facts? Scientists at Stanford decided to take a look.
Study first author Dr. Crystal Smith-Spangler said she is often asked by her patients whether organic food is worth the trouble. To get at the answer, she and her colleagues sifted through the scientific literature and found 17 studies comparing effects of organic and conventionally grown foods on human beings and 223 more that didn't involve people but examined the levels of nutrients and contaminants in the items.
The study, published in the Annals of Internal Medicine, included fruits, vegetables, eggs, grains, dairy, poultry and meat. Processed foods weren't part of the review.
Smith-Spangler, who is an instructor at Stanford's medical school and treats patients at the Veterans Affairs Palo Alto Health Care System, said the data didn't reveal too many differences. But there were a few:
Overall, based on three human studies, the scientists found no detectable difference in rates of allergies such as eczema. Very few studies examined clinical outcomes in this way.
In the case of nutrients, most studies were conducted on fruit and vegetables. "We did not find strong evidence that organic foods are consistently more nutritious than conventional foods," Smith-Spangler said. The exception was for levels of phosphorus, which were higher in organically grown produce.
Those differences are not likely to be of any health significance, she said. That's because "basically if you are eating you are getting enough phosphorus."
Organically grown food was also somewhat higher in total phenols, plant compounds that have antioxidant activity. These results varied a lot, however, possibly because of conditions under which plants were grown such as amounts of rainfall, soil type and ripeness at the time of harvesting.
There was also weak evidence that organic eggs and chickens contained higher levels of omega-3 fatty acids. But again, Smith-Spangler said, the data are scant and quite variable.
For pesticides residues, the authors found a 30% lower rate of detectable contamination in organically grown produce. Two studies found that children who ate conventional produce had higher levels of pesticide residues in their urine, and the levels fell when the children switched to organic foods.
But, again, it's not clear whether there would be clinical consequences, Smith-Spangler and coauthors wrote. Studies generally found that levels of contamination were within safe ranges and may not differ much between organic and conventionally grown food.
What about bacteria? The review did find higher rates of microbes resistant to multiple antibiotics in conventionally reared chicken and pork, but when considering non-drug-resistant E. coli, "both organic and conventionally grown foods were at similar risk for contamination," Smith-Spangler said.
"It's important to make clear that the studies included raw fruit and vegetable as well as chicken. Consumers should remember to use the usual safe food handling practices to avoid food-borne illnesses," she said.
And that means organic and conventional, produce as well as poultry. Brush up on the safety tips at the website of the Centers for Disease Control and Prevention.
Bottom line? “There isn’t much difference between organic and conventional foods, if you’re an adult and making a decision based solely on your health,” study senior author Dr. Dena Bravata of Stanford’s Center for Health Policy said in a release from the university.
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