Purpose: Although sales of organic foods have skyrocketed, there has been no robust analysis of the evidence comparing the health or safety of organic and conventional foods. This meta-analysis reviews the comparative health benefits and harms of organic and conventional foods.
Method: Searches were limited to English language articles from 1/1966- 05/2011 that compared human populations consuming organic and conventional foods and studies that compared nutrients, pesticides, bacteria, and fungal toxins found in unprocessed organic and conventional fruits, vegetables, grains, meats, milk and eggs. Summary risk differences and standardized mean differences were calculated when possible using random effects models.
Result: 5,908 relevant citations were identified; 237 studies met inclusion criteria: 17 studies of populations consuming organic and conventional diets; 223 studies of fruits, vegetables, grains, meats, milk, poultry, and eggs. Two studies reported significantly lower urinary pesticide levels among children consuming organic diets than conventional ones. The risk of contamination with detectable pesticide residues was 32% lower among organic than conventional produce (RD 95%CI: -37% to -26%; p<0.001; 9 studies), though differences in risk of exceeding maximum allowed limits may be small. Phosphorus levels were statistically (though not clinically) significantly higher in organic than conventional produce (SMD 0.82; 95%CI: 0.44 to 1.2; p<0.001; 7 studies). There was no difference in E. coli contamination risk between organic and conventional produce (RD 4%; 95%CI: -0.2% to 7.5%; p=0.061; 5 studies). Bacterial contamination of retail chicken and pork was common, but unrelated to farming method. However, the risk of isolating bacteria resistant to ≥ 3 antibiotics was 33% lower among organic than conventional chicken and pork (RD 95%CI: 21% to 45%; p<0.002; 5 studies). Many outcomes were reported by fewer than 10 studies, limiting the reliability of pooled results. The included studies were highly heterogeneous likely due to differences in sampling and testing methods, organic practices, and physical factors (e.g., weather, soil type).
Conclusion: The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional alternatives. Consuming organic produce may reduce pesticide exposures. Bacterial contamination of both organic and conventional animal products is common and underscores the need for adherence to food safety practices. Consumption of organic animal products may reduce exposure to antibiotic-resistant bacteria though the clinical significance of this finding is uncertain.
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