In 2010, The market for organics in the United States grew to $26.7 billion dollars, a spike from $3.7 billion in 1997. Some consumers turn to organic foods because of the perception that organically produced foods are more nutritious than conventional alternatives, but a study conducted by scientists at Stanford University did not find robust evidence to support this perception.
After analyzing 17 human studies and 223 studies on nutrient density and contamination levels, the study concluded that published literature lacks strong evidence that organic foods are significantly more nutritious. Choosing to consume organic foods, however, may reduce exposure to pesticides and antibiotic-resistant bacteria. According to the review, organic produce is 30% less likely to contain detectable pesticides compared to conventional produce. Still, the vast majority of all produce tested fell below government safety tolerances.
Five of the studies reviewed directly compared the rate of E. coli contamination, and the Stanford reviewers found no statistically significant difference between produce; 7% for organic and 6% for conventional. The differences in contamination between organic and conventional animal products were also statistically insignificant. The reviewers found that 67% of organic chicken samples and 64% of conventional samples were contaminated with Campylobacter (one of the most common causes of food poisoning), while 35% of organic and 34% of conventional samples were found to be contaminated with Salmonella. Additionally, the Stanford scientists found that 65% of organic and 49% of conventional samples of pork were contaminated with E. coli.
If there was one major difference, according to the study, it was contamination of conventional animal products with pathogens that were resistant to three or more antibiotics. The study found conventional samples of chicken and pork were 33% more at risk. The authors of the study write that the increased prevalence of antibiotic resistance may be related to the routine use of antibiotics in conventional animal husbandry, but add that the extent to which antibiotic use for livestock contributes to antibiotic-resistant pathogens in humans continues to be debated because inappropriate use of antibiotics is the major cause of antibiotic-resistant infections in humans.
The authors of the review advise that their results should be interpreted with caution, noting there have been no long-term studies of health outcomes for people who eat primarily organic food versus those who eat primarily conventional. As a result, they say drawing broad conclusions is difficult.