Little Evidence of Health Benefits of Organic Foods, Study Finds
You’re at the supermarket looking at a basket of sweet, juicy plums. You search for the conventionally grown stone fruit, then decide to spend an extra $1/pound on its organic cousin. You think you’ve just made the healthiest decision by going organic – but new findings from Stanford University cast doubt on your thinking.
“There’s not much difference between organic and conventional foods, if you’re an adult and you’re making a decision based on your health alone,” said Dena Bravata, MD, MS, lead author of a paper. comparing the nutrition of organic and non-organic foods, published in the September 4 issue of Annals of Internal Medicine.
A team led by Bravata, a senior fellow at 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-scientist at the 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 pose fewer health risks than conventional alternatives, although eating organic foods may reduce the risk of pesticide exposure.
The popularity of organic produce, which is typically grown without pesticides or synthetic fertilizers or the routine use of antibiotics or growth hormones, is skyrocketing in the United States. Between 1997 and 2011, organic food sales in the United States increased from $3.6 billion to $24.4 billion, and many consumers are willing to pay more for these products. Organic foods are often twice as expensive as their conventionally grown counterparts.
Although there is a common perception – perhaps based purely on price – that organic foods are better for you than non-organic ones, the question remains open as to the health benefits. In fact, the Stanford study stemmed from Bravata’s patients asking him again and again about the benefits of biologics. She didn’t know how to advise them.
So Bravata, who is also chief medical officer at healthcare transparency firm Castlight Health, did a literature search, uncovering what she called a “puzzling set of studies, some of which weren’t very rigorous, appearing in trade publications”. There was no comprehensive summary of the evidence including both benefits and harms, she said.
“It was an area ripe for 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 articles and identified 237 of the most relevant for analysis. These included 17 studies (including six randomized clinical trials) in populations consuming organic and conventional diets, and 223 studies comparing either nutrient levels or 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 the health outcomes of people consuming organic foods versus conventionally produced foods; the duration of 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 observed in the vitamin content of organic produce, and only one nutrient – phosphorus – was significantly higher in organic produce compared to conventionally grown produce (and the researchers note that, as few people are phosphorus deficient, it has little clinical significance) . There was also no difference in protein or fat content between organic and conventional milk, although evidence from a limited number of studies suggests that organic milk may contain significantly higher levels. of omega-3 fatty acids.
The researchers also weren’t able to identify specific fruits and vegetables where organic emerged as the healthier choice, despite running what Bravata called “tons of analysis.”
“Some think organic foods are always healthier and more nutritious,” said Smith-Spangler, who is also a medical instructor at the School of Medicine. “We were a little surprised not to find that.”
The review provided little evidence that conventional foods pose greater health risks than organic products. While researchers have found that organic produce has a 30% lower risk of pesticide contamination than conventional fruits and vegetables, organic food is not necessarily 100% pesticide free. Additionally, as the researchers noted, the pesticide levels of all foods were generally within allowable safe limits. Two studies of children consuming organic and conventional diets found lower levels of pesticide residues in the urine of children on an organic diet, although the significance of these findings for children’s 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 results mean for consumers, the researchers said their goal was to educate people, not discourage them from making organic purchases. “If you look beyond the health effects, there are many more reasons to buy organic products over conventional ones,” Bravata noted. She listed taste preferences and concerns about the effects of conventional farming practices on the environment and animal welfare among the reasons people choose organic produce.
“Our goal was to shed light on the evidence,” Smith-Spangler said. “This is information that people can use to make their own decisions based on their level of pesticide concern, budget and other considerations.”
She also said people should aim for healthier eating overall. She stressed the importance of eating fruits and vegetables, “regardless of culture,” noting that most Americans don’t get the recommended amount.
In discussing the limitations of their work, the researchers noted the heterogeneity of the studies they reviewed due to differences in testing methods; physical factors affecting food, such as weather and soil type; and wide variation between organic farming methods. With respect to the latter, there may be specific biological practices (e.g. how manure fertilizer, a risk of bacterial contamination, is used and handled) that could result in a safer, higher quality product. nutritional.
“What I’ve learned is there’s a lot of variation between farming practices,” Smith-Spangler said. “It appears that there are many different factors that are important in predicting nutritional quality and damage.”
Other Stanford co-authors are Margaret Brandeau, PhD, 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, Deputy Director of 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 Palo Alto Veterans Health Care System; medical librarian Christopher Stave, MLS; and Ingram Olkin, PhD, professor emeritus of statistics and education. The authors received no external funding for this study.