The health benefits of organic foods are unclear following a study conducted by researchers at Stanford university. The findings following a systematic review comparing evidence of the health effects of organic and conventional foods, has just been published in the journal, Annals of Internal Medicine, Volume 157, Number 5, 2012.
The study included all the main English language reports of comparisons of organically and conventionally grown food or of populations consuming these foods.
17 studies in humans and 223 studies of nutrient and contaminant levels in foods met inclusion criteria. Only 3 of the human studies examined clinical outcomes, finding no significant differences between populations by food type for allergic outcomes (eczema, wheeze, atopic sensitization) or symptomatic Campylobacter infection.
Two studies reported significantly lower urinary pesticide levels among children consuming organic versus conventional diets, but studies of biomarker and nutrient levels in serum, urine, breast milk, and semen in adults did not identify clinically meaningful differences.
All estimates of differences in nutrient and contaminant levels in foods were highly heterogeneous except for the estimate for phosphorus; phosphorus levels were significantly higher for organic foods than in conventional produce, although this difference was not clinically significant.
The risk for contamination with detectable pesticide residues was lower among organic than conventional produce (risk difference, 30% [CI, −37% to −23%]), but differences in risk for exceeding maximum allowed limits were small.
Escherichia coli contamination risk did not differ between organic and conventional produce. Bacterial contamination of retail chicken and pork was common but unrelated to farming method. However, the risk for isolating bacteria resistant to 3 or more antibiotics was higher in conventional than in organic chicken and pork (risk difference, 33% [CI, 21% to 45%]).
The studies were heterogeneous and limited in number, which may have affected aspects of the study.
The authors of the study concluded that the published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods. However, consumption of organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria.
Commenting on the study, Australian academic Liza Oates in Melbourne said there were still good reasons to eat organic foods. Ms Oates at RMIT University is currently conducting a PhD in the health effects of organic diets.
