Stanford Study: Little Evidence of Health Benefits from Organic Foods

No consistent differences were seen in the vitamin content of organic products, and only one nutrient — phosphorus — was significantly higher in organic versus conventionally grown produce.


You’re in the supermarket eyeing a basket of sweet, juicy plums. You reach for the conventionally grown stone fruit, then decide to spring the extra $1/pound for its organic cousin. You figure you’ve just made the healthier decision by choosing the organic product — but new findings from Stanford University cast some doubt on your thinking.

“There isn’t much difference between organic and conventional foods, if you’re an adult and making a decision based solely on your health,” said Dena Bravata, MD, MS, the senior author of a paper comparing the nutrition of organic and non-organic foods, published in the Sept. 4 issue of Annals of Internal Medicine.

A team led by Bravata, a senior affiliate with Stanford’s Center for Health Policy, and Crystal Smith-Spangler, MD, MS, an instructor in the school’s Division of General Medical Disciplines and a physician-investigator at VA Palo Alto Health Care System, did the most comprehensive meta-analysis to date of existing studies comparing organic and conventional foods. They did not find strong evidence that organic foods are more nutritious or carry fewer health risks than conventional alternatives, though consumption of organic foods can reduce the risk of pesticide exposure.

The popularity of organic products, which are generally grown without synthetic pesticides or fertilizers or routine use of antibiotics or growth hormones, is skyrocketing in the United States. Between 1997 and 2011, U.S. sales of organic foods increased from $3.6 billion to $24.4 billion, and many consumers are willing to pay a premium for these products. Organic foods are often twice as expensive as their conventionally grown counterparts.

Although there is a common perception — perhaps based on price alone — that organic foods are better for you than non-organic ones, it remains an open question as to the health benefits. In fact, the Stanford study stemmed from Bravata’s patients asking her again and again about the benefits of organic products. She didn’t know how to advise them.

So Bravata, who is also chief medical officer at the health-care transparency company Castlight Health, did a literature search, uncovering what she called a “confusing body of studies, including some that were not very rigorous, appearing in trade publications.” There wasn’t a comprehensive synthesis of the evidence that included both benefits and harms, she said.

“This was a ripe area in which to do a systematic review,” said first author Smith-Spangler, who jumped on board to conduct the meta-analysis with Bravata and other Stanford colleagues.

For their study, the researchers sifted through thousands of papers and identified 237 of the most relevant to analyze. Those included 17 studies (six of which were randomized clinical trials) of populations consuming organic and conventional diets, and 223 studies that compared either the nutrient levels or the bacterial, fungal or pesticide contamination of various products (fruits, vegetables, grains, meats, milk, poultry, and eggs) grown organically and conventionally. There were no long-term studies of health outcomes of people consuming organic versus conventionally produced food; the duration of the studies involving human subjects ranged from two days to two years.

After analyzing the data, the researchers found little significant difference in health benefits between organic and conventional foods. No consistent differences were seen in the vitamin content of organic products, and only one nutrient — phosphorus — was significantly higher in organic versus conventionally grown produce (and the researchers note that because few people have phosphorous deficiency, this has little clinical significance). There was also no difference in protein or fat content between organic and conventional milk, though evidence from a limited number of studies suggested that organic milk may contain significantly higher levels of omega-3 fatty acids.

The researchers were also unable to identify specific fruits and vegetables for which organic appeared the consistently healthier choice, despite running what Bravata called “tons of analyses.”

“Some believe that organic food is always healthier and more nutritious,” said Smith-Spangler, who is also an instructor of medicine at the School of Medicine. “We were a little surprised that we didn’t find that.”

The review yielded scant evidence that conventional foods posed greater health risks than organic products. While researchers found that organic produce had a 30 percent lower risk of pesticide contamination than conventional fruits and vegetables, organic foods are not necessarily 100 percent free of pesticides. What’s more, as the researchers noted, the pesticide levels of all foods generally fell within the allowable safety limits. Two studies of children consuming organic and conventional diets did find lower levels of pesticide residues in the urine of children on organic diets, though the significance of these findings on child health is unclear. Additionally, organic chicken and pork appeared to reduce exposure to antibiotic-resistant bacteria, but the clinical significance of this is also unclear.

As for what the findings mean for consumers, the researchers said their aim is to educate people, not to discourage them from making organic purchases. “If you look beyond health effects, there are plenty of other reasons to buy organic instead of conventional,” noted Bravata. She listed taste preferences and concerns about the effects of conventional farming practices on the environment and animal welfare as some of the reasons people choose organic products.

“Our goal was to shed light on what the evidence is,” said Smith-Spangler. “This is information that people can use to make their own decisions based on their level of concern about pesticides, their budget and other considerations.”

She also said that people should aim for healthier diets overall. She emphasized the importance of eating of fruits and vegetables, “however they are grown,” noting that most Americans don’t consume the recommended amount.

In discussing limitations of their work, the researchers noted the heterogeneity of the studies they reviewed due to differences in testing methods; physical factors affecting the food, such as weather and soil type; and great variation among organic farming methods. With regard to the latter, there may be specific organic practices (for example, the way that manure fertilizer, a risk for bacterial contamination, is used and handled) that could yield a safer product of higher nutritional quality.

“What I learned is there’s a lot of variation between farming practices,” said Smith-Spangler. “It appears there are a lot of different factors that are important in predicting nutritional quality and harms.”

Other Stanford co-authors are Margaret Brandeau, PhD, the Coleman F. Fung Professor in the School of Engineering; medical students Grace Hunter, J. Clay Bavinger and Maren Pearson; research assistant Paul Eschbach; Vandana Sundaram, MPH, assistant director for research at CHP/PCOR; Hau Liu, MD, MBA, clinical assistant professor of medicine at Stanford and senior director at Castlight Health; Patricia Schirmer, MD, infectious disease physician with the Veterans Affairs Palo Alto Health Care System; medical librarian Christopher Stave, MLS; and Ingram Olkin, PhD, professor emeritus of statistics and of education. The authors received no external funding for this study.

Information about Stanford’s Department of Medicine, which supported the work, is available at http://medicine.stanford.edu. The Center for Health Policy is a unit of the Freeman Spogli Institute for International Studies at Stanford.

--Michelle Brandt, Stanford News Service


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Amy Zucker Morgenstern September 05, 2012 at 02:02 PM
Two years? They looked at the health effects of consuming more pesticides and antibiotics and concluded that you'll be fine at the end of two years? That is not what I want to know. I want to know whether my daughter is more likely to get cancer at 40 if she eats non-organic food. Until researchers can answer that, I'm going to keep buying her the least toxic food available. Nutrition doesn't enter into it at all for me, and I'm always a little surprised that anyone thinks organic food will be higher in vitamins. Is this a claim producers often make? I appreciate Bravata's pointing out reasons that for me are the most important. I would add the welfare of workers. No one should be handling pesticide-covered fruit all day, or working in a field as crop dusters spray it.
Scott Van Duyne September 05, 2012 at 02:16 PM
A puzzling study. Why would anyone think organically-grown food would have more nutrients in it? The point is, it has less carcinogenic pesticides in it by construction. The study confirms this obvious point: "...can reduce the risk of pesticide exposure." I hope they didn't pay much for this ground breaking work.
commuter September 05, 2012 at 03:40 PM
I buy organic fruits and vegetables because they taste noticeably better than most department store produce. Don't know if this is because of fewer chemicals or better production values in general.
Beatrice Karnes September 05, 2012 at 03:53 PM
I agree with Scott that the most pertinent comment is "...can reduce the risk of pesticide exposure." I have fruit trees in my yard and a large vegetable garden--all grown organically. I take it a step further by purchasing fresh, ocean-caught fish from fishermen in Santa Cruz and Half Moon Bay. Can anyone recommend a rancher on the peninsula or in the south bay who raises grass-fed beef without hormones? I'd love to purchase directly from the rancher, putting more money into the pocket of the person responsible for raising the beef in a responsible manner.
Andreas Ramos September 05, 2012 at 04:10 PM
The only reason I choose organic food is because it doesn't have pesticides or hormones.
Phil Bordeaux September 06, 2012 at 04:07 AM
This had to do with nutrition value only looks like. The health effects of ingesting pesticide laden food is a long term affair. In addition it makes no measure of the social costs of massive pesticide use, the economic destruction wreaked on small farms by frankenfood or the fact that mass produce crap has little or no taste. I'm not a fanatical organic grower but I grow most of my own food. I try to coexist and share with the bugs when possible and minimize the use of chemical poisons. My food tastes better, I no longer need or take supplements and I lost 30 lbs so far without exercise. Eat what you want. I'm sold on at least making an effort to eat healthy.
Phil Bordeaux September 06, 2012 at 04:11 AM
Then again..looking at the credentials, these are the people who think pharmaceuticals are the panacea for the ills of humanity. Guess it's not surprise that legalized dope peddlers would be doing the scut work for Monsanto and Dowm corporate agribusiness and the like, after all.
Beatrice Karnes September 06, 2012 at 09:39 AM
Hi Phil, I repeat my earlier question--do you know a local rancher who raises grass-fed beef without hormones or antibiotics? Grass-fed tastes sooooo much better. I read a study years ago by the University of Wisconsin which found that grass fed beef had as many Omega 3s as fish! I was stunned. Beef is as healthy as wild-caught fish if we only allow the cattle to graze naturally.
Sherri Bohan September 06, 2012 at 05:29 PM
There are a couple that I know of http://www.morrisgrassfed.com/ is south of Gilroy. Also contact Santa Clara County Cattlemen Association (there are alot of cattlewomen in the association too)
Beatrice Karnes September 06, 2012 at 10:51 PM
Thank you, Sherri. I'll check them out!
Bob Silvestri September 18, 2012 at 10:58 PM
Chuck Benbrook of the Organic Center published a response to the Stanford study: http://www.organicconsumers.org/benbrook_annals_response2012.pdf, and Common Dreams reported today on Cornucopia Institute research on the funders of the Stanford study, which include Monsanto and the industrial agriculture conglomerate Cargill. http://www.commondreams.org/newswire/2012/09/12-8
Bob Silvestri September 18, 2012 at 10:59 PM
Why the Stanford Organic Food Meta-Analysis is 'Scientific' Nonsense http://millvalley.patch.com/blog_posts/the-stanford-organic-food-meta-study-is-scientific-nonsense
Bob Silvestri September 19, 2012 at 05:02 PM
Reuters - Study finds multiple types of tumors in rats fed on Monsanto's GM corn http://www.reuters.com/article/2012/09/19/us-gmcrops-safety-idUSBRE88I0L020120919
Beatrice Karnes September 19, 2012 at 05:18 PM
Hi Bob, You should sign up to blog on Palo Alto Patch.


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