Author(s): Charles Benbrook, Ph.D. Chief Scientist, The Organic Center
Donald R. Davis, PhD. Retired Research Scientist, University of Texas at Austin
Preston K. Andrews, Department of Horticulture and Landscape Architechture, Washington State University
An advance copy of a study appeared today that will be published in the September edition of the "American Journal of Clinical Nutrition." The published paper, "Nutritional quality of organic foods: a systematic review," was written by a team led by Alan Dangour, at the London School of Hygiene and Tropical Medicine and funded by the United Kingdom's Food Standards Agency (FSA).In their written report, the London team downplayed positive findings in favor of organic food. In several instances, their analysis showed that organic foods tend to be more nutrient dense than conventional foods. Plus, their study omitted measures of some important nutrients, including total antioxidant capacity. It also lacked quality controls contained in a competing study released in 2008 by The Organic Center (TOC). Last, the FSA-funded team also used data from very old studies assessing nutrient levels in plant varieties that are no longer on the market.
The London team reported finding statistically significant differences between organically and conventionally grown crops in three of thirteen categories of nutrients. Significant differences cited by the team included nitrogen, which was higher in conventional crops, and phosphorus and tritratable acids, both of which were higher in the organic crops. Elevated levels of nitrogen in food are regarded by most scientists as a public health hazard because of the potential for cancer-causing nitrosamine compounds to form in the human GI tract. Hence, this finding of higher nitrogen in conventional food favors organic crops, as do the other two differences. Despite the fact that these three categories of nutrients favored organic foods, and none favored conventionally grown foods, the London-based team concluded that there are no nutritional differences between organically and conventionally grown crops.
A team of scientists convened by The Organic Center (TOC) carried out a similar, but more rigorous, review of the same literature. The TOC team analyzed published research just on plant-based foods. Results differ significantly from the more narrow FSA review and are reported in the study "New Evidence Confirms the Nutritional Superiority of Plant-Based Organic Foods."
The TOC findings are similar for some of the nutrients analyzed by the FSA team, but differ significantly for two critical classes of nutrients of great importance in promoting human health – total polyphenols, and total antioxidant content. The FSA team did not include total antioxidant capacity among the nutrients studied, and it found no differences in the phenolic content in 80 comparisons across 13 studies.
Unlike the London study, The Organic Center review focused on nutrient differences in "matched pairs" of crops grown on nearby farms, on the same type of soil, with the same irrigation systems and harvest timing, and grown from the same plant variety. It also rigorously screened studies for the quality of the analytical methods used to measure nutrient levels, and eliminated from further consideration a much greater percentage of the published literature than the FSA team.
While the FSA team found 80 comparisons of phenolic compounds, the TOC team focused on the more precise measure of total phenolic acids, or total polyphenols, and found just 25 scientifically valid "matched pairs." By mixing together in their statistical analysis the results of several specific phenolic acids, the FSA team likely lost statistical precision. Instead, the TOC team focused on studies reporting values for total phenolic acids, and also applied more rigorous selection criteria to exclude poorer quality studies.
The TOC team found –
Twenty-five matched pairs of organic and conventional crops for which total phenolic acid data was reported. The levels were higher in the organic crops in 18 of these 25 cases, conventional crops were higher in 6. In five of the matched pairs, phenolic acid levels were higher in organic crops by 20% or more. On average across the 25 matched pairs, total phenolics were 10% higher in the organic samples, compared to conventional crops.
In seven of eight matched pairs reporting total antioxidant capacity data, the levels were higher in the organically grown crop. Of 15 matched pairs for the key antioxidant quercetin, 13 reported higher values in the organic food. In the case of kaempferol, another important antioxidant, the organic samples were higher in six cases, while five were higher in the conventional crops.
In the TOC study, there were an ample number of matched pairs to compare the levels of 11 nutrients, including five of the nutrients in the FSA review. For the five nutrients covered in each review, the TOC team was in general agreement with the FSA findings for two (nitrogen and phosphorus).The London team did not assess differences in key individual antioxidants, nor in total antioxidant activity, important nutrients that have been measured in several more recent studies.
Across all the valid matched pairs and the 11 nutrients included in the TOC study, nutrient levels in organic food averaged 25% higher than in conventional food. Given that some of the most significant differences favoring organic foods were for key antioxidant nutrients that most Americans do not get enough of on most days, the team concluded that the consumption of organic fruits and vegetables, in particular, offered significant health benefits, roughly equivalent to an additional serving of a moderately nutrient dense fruit or vegetable on an average day.
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