September 5, 2012 — Although eating organic foods may reduce exposure to pesticides and antibiotic-resistant bacteria, there is no conclusive evidence that they are more nutritious than conventional foods, according to a new systematic review.
Crystal Smith-Spangler, MD, from the Center for Health Policy and Center for Primary Care and Outcomes Research, Stanford University, California, and colleagues report their results in the September 4 issue of the Annals of Internal Medicine.
The researchers identified 223 studies that evaluated the nutrient and contaminant levels in foods and 17 studies in humans conducted between 1966 and 2011. The researchers found no differences in vitamin and nutrient levels (eg, ascorbic acid, calcium, fiber) between organic and conventional plant and animal products. Phosphorous was the only nutrient found to be higher in organic produce compared with conventional produce (standardized mean difference, 0.82; 95% confidence interval [CI], 0.44 - 1.20; P < 0.001); however, the authors note that this was of little clinical significance.
The risk for contamination with Salmonella and Campylobacter was the same between organic and conventional chicken and pork, but the risk for exposure to antibiotic-resistant bacteria was higher in conventionally farmed chicken and pork (risk difference [RD], 33%; 95% CI, 21% - 45%; P < .001). In addition, the risk for pesticide contamination was lower among organic vs conventional produce (RD, 30%; 95% CI, −37% to −23%; P < .001). However, pesticide levels fell within allowable safety limits for all foods in all but 3 studies.
Overall, the risk for contamination with Escherichia coli was similar between organic and conventional produce (RD, 2.4%; 95% CI, −1.5% to 6.2%; P = 1.00) in the 5 studies that evaluated the outcome. However, when the single study that found that a higher risk for contamination in conventional produce was removed in the sensitivity analysis, the researchers found a 5% greater risk for contamination among organic produce (RD, 5.1%; 95% CI, 2.92% - 7.18%; P < .001).
"Consumers purchase organic foods for many reasons. Despite the widespread perception that organically produced foods are more nutritious than conventional alternatives, we did not find robust evidence to support this perception," Dr. Smith-Spangler and colleagues write.
The study authors conducted a literature search of 6 databases (MEDLINE, EMBASE, CAB Direct, Agricola, TOXNET, and Cochrane Library) to find peer-reviewed studies. Studies were eligible for inclusion "if they reported a comparative evaluation of populations consuming diets of foods grown organically and conventionally or a comparative evaluation of nutrient levels or bacterial, fungal, or pesticide contamination of fruits, vegetables, grains, meats, poultry, milk (including raw milk), or eggs grown organically and conventionally." Studies that evaluated samples from livestock feces or gastrointestinal tracts, studies of processed foods, and studies that did not report statistical tests or report information about variance were excluded.
Overall, the researchers found highly heterogeneous results of estimates of differences in nutrient and contaminant levels in foods. Two studies reported lower urinary pesticide levels among children receiving organic vs conventional diets.
The authors acknowledge that the heterogeneous nature of the study methods, physical factors (eg, season or soil type), and variation within organic practices makes drawing definitive conclusions from these data difficult. The researchers also note that there have been no long-term studies evaluating the health benefits of consuming a predominately organic vs a conventionally farmed diet.
"The evidence does not suggest marked health benefits from consuming organic versus conventional foods, although organic produce may reduce exposure to pesticide residues and organic chicken and pork may reduce exposure to antibiotic-resistant bacteria," the study authors conclude.
The authors have disclosed no relevant financial relationships.
Ann Intern Med. 2012;157:348-366. Full text
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Cite this: Organic Foods: Less Pesticide Exposure, Same Nutrition - Medscape - Sep 05, 2012.