IS THERE A DIFFERENCE BETWEEN ORGANIC AND CONVENTIONAL ANIMAL PRODUCTS? A SYSTEMATIC REVIEW OF THE HEALTH BENEFITS AND HARMS

Purpose: Despite costing over twice as much as conventional alternatives, sales of organic meats, milk, and eggs have skyrocketed without detailed evidence of increased safety or higher nutritional quality. We sought to evaluate the health benefits and harms of organic and conventional animal products.

Method: We performed a systematic review of the benefits and harms of organic and conventional animal products. We considered English-language studies (indexed: 1/1966-8/2009) eligible for inclusion if they reported either a comparative evaluation of people consuming animal products raised organically and conventionally or a comparative evaluation of the animal products themselves (we excluded processed foods). When possible, we calculated summary odds ratios using random effects models. 

Result: Searches identified 5,371 potentially relevant citations; 25 studies met inclusion criteria. 2 studies from a Dutch birth cohort directly compared the health outcomes of consumers of principally organic and conventional animal products: There was no association between the overall diet of 2764 pregnant women and their infants and the development of eczema, wheeze, or serum IgE levels. In a subgroup analysis, children who consumed >90% of dairy products from organic sources had lower risk of eczema at age 2 years than children who consumed <50% of diary products from organic sources (OR 0.64; 95% CI 0.44-0.93). Mothers consuming >90% of dietary dairy and meat of organic origin had higher levels of conjugated linoleic acid (p<0.001) and trans-vaccenic acids (p=0.015) in their breast milk than women consuming conventional diets.                                                                                                                                          23 studies evaluated the animal products themselves and found no significant difference in bacterial contamination between organic and conventional meats, milk or eggs (OR 1.10; 95% CI 0.93-1.30). However, Campylobacter, Enterococcus, and Staphlococcus spp and E. coli cultured from organic products were less likely to be antibiotic resistant than bacteria cultured from conventional poultry, beef, pork, and milk (p<0.001). There was no significant difference in heavy metal contamination or vitamin content of organic and conventional meat products.

Conclusion: Too few studies have compared outcomes among consumers of organic and conventional animal products to draw conclusions about their health effects. Although bacterial contamination does not differ significantly between organic and conventional animal products, bacteria cultured from conventional products are more likely to be antibiotic resistant. The clinical significance of this increased antibiotic resistance is unknown.