Researchers from Stanford University analysed 237 existing studies, 17 of which were ‘human’ studies of organic and conventional diets – including six randomised trials – and the rest of which compared nutrient and contamination levels in organic and conventional foods.
They found that there was no strong evidence that organic foods “are more nutritious or carry fewer health risks than conventional alternatives”.
“Some believe that organic food is always healthier and more nutritious,” said co-author Crystal Smith-Spangler MD, MS, an instructor in Stanford’s Division of General Medical Disciplines. “We were a little surprised that we didn’t find that.”
Looking at meat and poultry products, the report’s authors said there was no significant difference between vulnerability to symptomatic campylobacter infection among populations that consumed organic meat and those that consumed conventional meats.
Bacterial contamination of retail chicken and pork was found to be “common but unrelated to farming methods”, while E.coli contamination risk did not differ between organic and conventional produce.
Researchers did find there was a lower risk of antibiotic-resistant bacteria in organic chicken and pork, but said the clinical significant of this was “unclear”.
Co-author Dena Bravata, MD, MS, a senior affiliate with Stanford’s Center for Health Policy, said that by publishing the findings, Stanford was not intending to discourage people from buying organic produce. “If you look beyond health effects, there are plenty of other reasons to buy organic instead of conventional,” she said, pointing out that concerns over the environment and animal welfare might be other reasons to choose organic products.
The researchers also admitted that their report may be limited by the heterogeneity of the studies they reviewed, due to differences in testing methods, physical factors affecting the food – such as weather and soil types – and big variations in organic farming methods.
“What I learned is there’s a lot of variation between farming practices,” said Smith-Spangler. “It appears there are a lot of different factors that are important in predicting nutritional quality and harms.”