Demand for organic foods is partially driven by consumers' perceptions that they are more
nutritious. However, scientific opinion is divided on whether there are significant nutritional
differences between organic and non-organic foods, and two recent reviews have concluded that
there are no differences. In the present study, we carried out meta-analyses based on 343
peer-reviewed publications that indicate statistically significant and meaningful differences
in composition between organic and non-organic crops/crop-based foods. Most importantly, the
concentrations of a range of antioxidants such as polyphenolics were found to be substantially
higher in organic crops/crop-based foods, with those of phenolic acids, flavanones, stilbenes,
flavones, flavonols and anthocyanins being an estimated 19 (95 % CI 5, 33) %, 69 (95 % CI 13,
125) %, 28 (95 % CI 12, 44) %, 26 (95 % CI 3, 48) %, 50 (95 % CI 28, 72) % and 51 (95 % CI 17,
86) % higher, respectively. Many of these compounds have previously been linked to a reduced
risk of chronic diseases, including CVD and neurodegenerative diseases and certain cancers, in
dietary intervention and epidemiological studies. Additionally, the frequency of occurrence of
pesticide residues was found to be four times higher in conventional crops, which also
contained significantly higher concentrations of the toxic metal Cd. Significant differences
were also detected for some other (e.g. minerals and vitamins) compounds. There is evidence
that higher antioxidant concentrations and lower Cd concentrations are linked to specific
agronomic practices (e.g. non-use of mineral N and P fertilisers, respectively) prescribed in
organic farming systems. In conclusion, organic crops, on average, have higher concentrations
of antioxidants, lower concentrations of Cd and a lower incidence of pesticide residues than
the non-organic comparators across regions and production seasons.
