Is buying organic food worth the premium?
That depends on your personal priorities … and reliable information about the nutrition, health, and safety distinctions between organic and conventional foods.
Comparisons of the levels of vitamins and minerals in organic and conventional crops have always produced mixed results.
Sadly, most media reports concerning a new evidence review stress that point and downplay its affirmation of key health advantages for organic foods.
Researchers from Stanford University analyzed the existing studies comparing organic and conventional produce, grains, meats, and milk (Smith-Spangler C et al. 2012).
They called the result the most comprehensive “meta-analysis” conducted to date. In general, it echoes the findings of prior evidence reviews.
Unfortunately, their conclusions and press materials focus on the uncontroversial fact that organic produce does not offer consistently higher levels of vitamins and minerals.
Negative spin belied by the full findings
Even though the Stanford team's analysis confirmed that organic foods hold significant health advantages, senior author Dena Bravata, MD, MS put a misleadingly negative spin on their findings:
“There isn't much difference between organic and conventional foods, if you're an adult and making a decision based solely on your health.” (SUMC 2012)
But that assertion rests almost entirely on the lack of a consistent nutritional (vitamin/mineral) advantage for organic produce … although vitamin/mineral levels have as much or more to do with variations in the nutrient levels of differing cultivars and soils as with the farming methods used.
(Phosphorus levels were significantly and consistently higher in organically grown produce, but this may not matter much because few people lack phosphorous.)
But vitamin/mineral content is not the only – or the most critical – difference between organic and conventional crops, meats, and milk … see “Authors confirm key organic advantages” and “Organic foods' safety advantage affirmed”, below.
The researchers admitted the difficulty of comparing the studies due to differences in testing methods, weather conditions, cultivar (i.e., different strains of the same crop), ripeness, and soil type … a problem exacerbated by large variations among organic farming methods.
They noted that specific organic practices – such as the way that manure fertilizer, a risk for bacterial contamination, is used and handled – could yield a safer product of higher nutritional quality.
As co-lead author Crystal Smith-Spangler, M.D., said, “What I learned is there's a lot of variation between farming practices. It appears there are a lot of different factors that are important in predicting nutritional quality and harms.” (SUMC 2012)
For example, certain strains of carrots are always higher in beta-carotene, regardless of the farming method used.
Likewise, the mineral content of a food crop is partly determined by the cultivar being grown and by the mineral content of the soil in which it's grown, regardless of the farming method used.
Let's take a closer look at their findings, and the distortions in the authors' emphases and public statements.
Authors confirm key organic advantages
For their study, the researchers sifted through thousands of papers and identified 237 of the most relevant to analyze (Smith-Spangler C et al. 2012).
Those included 17 studies – six of which were randomized clinical trials – in which people consumed organic and conventional diets.
The other 223 studies 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.
Crucially, the Stanford analysis confirmed that organic produce typically contains more of the “antioxidant” compounds known as polyphenols.
Polyphenols influence gene switches (transcription factors) in ways shown to reduce inflammation and free radicals … and that may help prevent heart disease, dementia, diabetes, and cancer.
(See “Organic Crops Win for Antioxidants ... Again”, “Strawberries Curb Cancer Cell Growth; Organic Berries Called Best”, and “Organic Crops' Nutrition Advantage”.)
And the authors acknowledged the limited evidence suggesting that on average, organic milk provides significantly higher levels of omega-3 fatty acids (though not more protein or other nutrients) ... see “Organic Produce and Milk Offer More Antioxidants and Omega-3s”.
Organic foods' safety advantage affirmed
The reviewers said they found scant evidence that organic foods are safer than conventional products.
However, they based that assertion on the fact that pesticide residues on conventional fruits and vegetables typically fall under the established safety limits.
The shortcomings of U.S. pesticide-residue safety limits are well known. These include a dearth of evidence for many older pesticides, and a virtual absence of studies examining the combined effects of multiple pesticides.
The Stanford team noted that studies find lower levels of pesticide residues in the urine of children on organic diets.
Given that several recent studies have detected brain or developmental deficits linked to pesticide exposure, it seems very odd that the Stanford team chose to downplay the significance of those findings.
Also, as we reported (see “Organic Poultry Farms Curb Drug-Resistant Bugs”,) the Stanford team concluded that organic chicken and pork bear less antibiotic-resistant bacteria … but the clinical significance of this is unclear, since cooking kills bacteria.
Yet, the authors of the Stanford review – and the news media – chose to downplay the positive and accentuate the negative.
Bouchard MF, Chevrier J, Harley KG, Kogut K, Vedar M, Calderon N, Trujillo C, Johnson C, Bradman A, Barr DB, Eskenazi B. Prenatal exposure to organophosphate pesticides and IQ in 7-year-old children. Environ Health Perspect. 2011 Aug;119(8):1189-95. Epub 2011 Apr 13.
Bourn D, Prescott J. A comparison of the nutritional value, sensory qualities, and food safety of organically and conventionally produced foods. Crit Rev Food Sci Nutr. 2002 Jan;42(1):1-34. Review.
Magkos F, Arvaniti F, Zampelas A. Organic food: buying more safety or just peace of mind? A critical review of the literature. Crit Rev Food Sci Nutr. 2006;46(1):23-56. Review.
Perera FP, Rauh V, Whyatt RM, Tang D, Tsai WY, Bernert JT, Tu YH, Andrews H, Barr DB, Camann DE, Diaz D, Dietrich J, Reyes A, Kinney PL. A summary of recent findings on birth outcomes and developmental effects of prenatal ETS, PAH, and pesticide exposures. Neurotoxicology. 2005 Aug;26(4):573-87. Review.
Rauh V, Arunajadai S, Horton M, Perera F, Hoepner L, Barr DB, Whyatt R. Seven-year neurodevelopmental scores and prenatal exposure to chlorpyrifos, a common agricultural pesticide. Environ Health Perspect. 2011 Aug;119(8):1196-201. Epub 2011 Apr 12.
Rauh VA, Perera FP, Horton MK, Whyatt RM, Bansal R, Hao X, Liu J, Barr DB, Slotkin TA, Peterson BS. Brain anomalies in children exposed prenatally to a common organophosphate pesticide. Proc Natl Acad Sci U S A. 2012 May 15;109(20):7871-6. Epub 2012 Apr 30.
Smith-Spangler C et al. Are Organic Foods Safer or Healthier Than Conventional Alternatives?: A Systematic Review. Ann Intern Med. 4 September 2012;157(5):348-366. Accessed at http://annals.org/article.aspx?articleid=1355685
Stanford University Medical Center (SUMC). Little evidence of health benefits from organic foods, Stanford study finds. September 3, 2012. Accessed at http://www.eurekalert.org/pub_releases/2012-09/sumc-le082812.php
Zhao X, Chambers E 4th, Matta Z, Loughin TM, Carey EE. Consumer sensory analysis of organically and conventionally grown vegetables.J Food Sci. 2007 Mar;72(2):S87-91.