Background and methodology:
Organic foods are grown and produced according to specified standards that limit pesticide and herbicide use in crop production and drug use in livestock rearing. Previous reviews have concluded that organically produced foods have a nutrient composition superior to that of conventional foods, although this finding has not been consistent. To date, there has been no systematic review of the available published literature on this topic.
Researchers at the London School of Hygiene & Tropical Medicine conducted a systematic review of all published studies that reported the chemical analysis of foodstuffs produced using organic or conventional methods of cultivation over the past 50 years (between 1958 and 2008). The quality of research and reporting in this area was found to be extremely variable, which raises a question about the validity of the conclusions drawn by these studies. From a total of 52,471 articles, the researchers identified 162 studies related to nutrient content of organic and conventionally produced foods, of which 55 were of satisfactory quality. The contents of nutrients (such as vitamin C, calcium, and zinc) and other nutritionally relevant substances (such as phenolic compounds) reported in studies of satisfactory quality were analyzed, looking at differences between organically and conventionally produced foodstuffs.
When analyzed for their nutrient content, the crops from which the foodstuffs were produced showed no differences between organic and conventional in terms of their vitamin C, magnesium, calcium, potassium, zinc, or copper content. Conventional crops were found to contain more nitrogen than did organic, and organic crops had higher phosphorus and acidity than did conventional crops. When only animal-sourced foods were considered, the review found no evidence of a difference in nutrient content. The authors of this research review concluded that “there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs”. They also suggested that any claims about the benefits to the public and to environmental health from organic growing and processing methods warrant further review.
Dangour, A. D., Dodhia, S. K., Hayter, A., Allen, E., Lock, K., Uauy, R. (2009). Nutritional quality of organic foods: A systematic review. American Journal of Clinical Nutrition, 2009. Available on-line at: http://www.ajcn.org/cgi/rapidpdf/ajcn.2009.28041v1.