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A widely reported Stanford University study concluding there is little difference in the healthfulness and safety of conventional and organic foods has been criticized by experts in the environmental health sciences for overlooking the growing body of evidence on the adverse effects of pesticides. Critics take to task the authors’ omission of relevant studies and over interpretation of the data.

The meta-analysis of 237 studies, published in the September 2012
Annals of Internal Medicine, largely focused on nutrient content and viral/bacterial/fungal contamination of organic versus conventionally grown foods. Nine studies reporting pesticide residues, including three of residues exceeding federal limits, were included in summary analysis.

The authors concluded that the studies reviewed do not support what they call the “widespread perception” that organic foods overall are nutritionally superior to conventional ones, although eating an organic diet may reduce exposures to pesticides and antibiotic-resistant bacteria. A Stanford press release quoted senior author Dena Bravata as saying, “There isn’t much difference between organic and conventional foods, if you’re an adult and making a decision based solely on your health.”2 (According to the Stanford Medical Center press office, Bravata is no longer doing interviews about the study.)

In one key finding, the team reported a “risk difference” of 30% between conventional and organic produce, meaning organic produce had a 30% lower risk of pesticide contamination than conventional produce. That number was based on the difference between the percentages of conventional and organic food samples across studies with any detectible pesticide residues (38% and 7%, respectively).

But the concept of risk difference is potentially misleading in this context, as the metric does not refer to health risk, according to Charles Benbrook, research professor and program leader for Measure to Manage (M2M): Farm and Food Diagnostics for Sustainability and Health at Washington State University. Furthermore, says Benbrook, “Pesticide dietary risk is a function of many factors, including the number of residues, their levels, and pesticide toxicity,” not just whether contamination was present.