The line dividing organically grown foods and conventionally grown foods just got a little blurrier. A study was recently conducted by researchers at the London School of Hygiene and Tropical Medicine and published in the American Journal of Clinical Nutrition (“Nutritional quality of organic foods: a systematic review,” 2009 Jul 29). Suffice to say, their conclusion-that organically grown foods are “unlikely” to “provide any health benefit” to consumers-has effectively re-ignited the debate surrounding the nutritional superiority of organic foods.

The research was led by the school’s Alan Dangour, MSc, PhD, RPH, Nutr, senior lecturer, and was commissioned and funded by Britain’s Food Standards Agency (FSA), the governmental office that regulates food production and sales in Britain. It consisted of a systematic analysis of PubMed, Web of Science and CAB Abstracts-a total of 52,471 articles-spanning a period of 50 years from January 1958 to February 2008. Researchers included peer-reviewed articles with English abstracts in the analysis if they reported nutrient content comparisons between organic and conventional foodstuffs. Two reviewers extracted study characteristics, quality and data and the analyses were restricted to the most commonly reported nutrients.

Researchers pared the 52,471 articles down to 162 studies (which were comprised of 137 crop studies and 25 livestock product studies). Of those 162 studies, 55 were deemed to be of “satisfactory quality.” During the course of the analysis it was noted that conventionally produced crops had a significantly higher content of nitrogen, while organically produced crops had a significantly higher content of phosphorus and higher titratable acidity-a discrepancy that was attributed to differences in fertilizer use. The researchers reported “no evidence of a difference” detected for the remaining 8 of 11 crop nutrient categories analyzed.

Analysis of the more limited database on livestock products found no evidence of a difference in nutrient content between organically and conventionally produced livestock products.

Based on their systematic review, the London School of Hygiene and Tropical Medicine researchers concluded that “there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs. The small differences in nutrient content detected are biologically plausible and mostly relate to differences in production methods.”

The Fallout

Needless to say, the FSA study’s conclusion was swiftly met with criticism. Charles Benbrook, PhD, chief scientist with The Organic Center of Boulder, CO, issued a statement that warned, “Left unchallenged, the UK team’s study and Dr. Dangour’s remarks could erode consumer confidence in the inherent nutritional and health benefits of organic food…Among the multiple missteps in the FSA’s analysis are a failure to properly assess differences in the levels of key polyphenols and antioxidants and not using stringent guidelines to determine whether the studies are scientifically valid.”

Dr. Benbrook went on to refute the claim made by Dr. Dangour and his UK colleagues that the nutritional benefits of organic food are “not important, citing The Organic Center’s March 2008 report, which covered many of the same studies comparing nutrient levels in organic and conventional foods. “We confirmed that organic foods were, on average, 25% higher across 11 key nutrients compared to conventional foods,” said Dr. Benbrook. “Significant new science released since early 2008, the cut-off date for studies included in both the FSA’s and our study, provide additional strong support for the conclusion that organic foods offer nutritional and public health benefits.”

He also touched on the fact that the FSA study neglected to address the health benefits associated with the absence of pesticides in organic foods. In a separate report released in May 2009, The Organic Center analyzed dozens of studies, the majority published in the last three years, which collectively showed exposure to pesticides during pregnancy and the first years of life increases the risk of obesity, neurological problems and diabetes. “With the average American child exposed to 10 to 13 pesticides daily in food and drink and the rate of new diabetes cases doubling in the last decade, reducing pesticides in children’s foods is a top public health priority,” said Dr. Benbrook.

He also called upon government bodies, academic institutions, business leaders and consumers to join them in contesting “this incomplete and flawed analysis” of the benefits of organic food and farming.

In response to the criticism, Dr. Dangour issued statements of his own. “We are neither pro- nor anti-organic,” he said. “We are scientists interested in presenting and evaluating the strength of the existing evidence. Systematic reviews are recognized to be an enormously powerful tool for summarizing and presenting data from large amounts of studies. We are independent of the Food Standards Agency (FSA) and our work has been extensively externally peer-reviewed and has been published in the world’s leading nutrition journal.”

He went on to say that he and his team set out to answer specific questions about the nutrient content of organic foods and the putative nutrition-related health benefits of organic food consumption. “These are important questions from a public health nutrition perspective, and prior to our reports no systematic reviews had been conducted which included all of the available evidence. We clearly define the scope of each review in the opening paragraph of the executive summaries available online,” he explained. “Our reviews did not include information on pesticide and herbicide residue content or the environmental impacts of agricultural production methods. This is clearly stated in the opening paragraph of the executive summaries of the reports available online.”

With regard to The Organic Center’s assertion that pesticide use impacts health, Dr. Dangour stated that the nutritional content and chemical residue content of organic foods are separate questions. “Both questions are worthy of asking,” he said. “In our reviews, we asked only about nutritional content.”

In defense of his team’s systematic study selection process, he countered, “We clearly state in our protocol that the cut-off date for inclusion in our review on nutrient content was 29th February 2008. We posted the review protocol online on 18th April 2008. We informed many relevant stakeholder groups and contacted key academic experts asking them to provide published and in-press articles for inclusion. Any relevant reports published in peer-reviewed journals prior to the 29th February 2008 were included in our review.”

Dr. Dangour concluded by acknowledging that more research into the differences separating organic food from conventional food is warranted. “We heartily agree that more good quality research is needed,” he said. “We were disappointed that only one third of all identified studies met the basic criteria we defined for ‘satisfactory’ quality, and we would welcome an increase in the quality of research in this area.”