Organic Food Study Is Flawed, Conclusions Unsupported by Science

Published November 1, 2008

Charles Benbrook, chief scientist of the Organic Trade Association’s Organic Center, and his colleagues have published a 53-page report misleadingly titled “New Evidence Confirms the Nutritional Superiority of Plant-Based Organic Foods.”

The importance of this work was underscored by a foreword from none other than health guru Andrew Weil, M.D., who also happens to be a member of the Organic Center’s Board of Directors.

Weil considers it “the first in-depth review of the published scientific literature on the nutritional benefits of organic food completed since 2003.”

My own review of the study, however, shows it to be riddled with flaws and its conclusions unsupported.

Reviewed Others’ Research

Benbrook and his colleagues reviewed the literature on research comparing nutritional differences between organically grown fruits and vegetables and their conventionally grown counterparts, using total phenolics (a type of organic chemical compound) content, antioxidant capacity, and concentrations of two naturally occurring antioxidants (quercetin and kaempferol) as indicators of antioxidant activity.

Three vitamins or their precursors (ascorbic acid/vitamin C, beta-carotene, and vitamin E), two minerals (potassium and phosphorous), protein content, and nitrate concentration were also measured. Higher nitrate content was considered “undesirable.”

The authors identified 236 valid matched pairs (on the basis of criteria they set up) and found, on average, essentially no or very little difference—10 percent or less between the two cropping systems for total phenolics, ascorbic acid (vitamin C), beta-carotene, kaempferol, potassium, phosphorous, and protein.

Vitamin E content and antioxidant capacity were 15 percent and 24 percent higher, respectively, in the organically grown crops, but the two largest differences were found for the antioxidant quercetin (which was 140 percent higher, on average, in the organic crops) and the “undesirable” constituent nitrate, which was 80 percent higher in the conventional crops.

Mostly on the basis of these four comparisons, Benbrook and his coauthors concluded organic crops contained about 25 percent more of the nutrients measured in their study than comparable foods produced by conventional farming methods, and that organic plant-based foods were “more nutritious” as “validated by this study’s rigorous methodology.”

Lack of Scientific Rigor

My own review of this study showed it to be neither rigorous nor able to support the 25 percent “more nutritious” claim.

The study suffers from numerous defects, such as inclusion of publications that were not peer-reviewed, studies where the differences in nutrient content between organic and conventional produce were not statistically significant, and publications with insufficient information for statistical analysis.

In some cases the study failed to include results favorable to conventional farming while including data from organically grown food that is unavailable to consumers and/or inedible and thus arguably irrelevant.

Peer review is important in the publication of any new scientific material because it allows other scientists the opportunity to question the methodology, results, and conclusions of the publication’s authors before publication is permitted. While the process is far from perfect, it is at the very least a first line of defense against shoddy scientific research.

Similarly, establishment of statistical significance is important for research scientists who are trying to determine whether the differences they found in their investigations are real or occurred simply by chance.

Conventional Crops Actually Better

Organic consumers choose to spend 50 to 300 percent more for fruits and vegetables, a choice influenced in part by a desire to feed their families more nutritious food. These consumers deserve scientific information that is based on competent, peer-reviewed research that has been determined to be of statistical significance.

In my analysis of the publications Benbrook and his coauthors used, I calculated there were no differences in nutrient content between the organically and conventionally grown crops. In fact, the conventional half of the matched pairs came out 2 percent better.

An explanation of these calculations, plus critiques of some of the original research cited by Benbrook and colleagues, are detailed in my full report on the American Council on Science and Health Web site (see Internet Info below).

Statistical Sleight of Hand

In one example of easily misinterpreted results from organic-vs.-conventional studies, huge increases in quercetrin (a metabolic precursor of quercetin) in five organically grown vegetables were reported by Japanese investigators. These comparisons are invalid, however, because the organic vegetables were sprayed with chitosan whenever there were signs of insect infestation, while the conventional vegetables were not so treated.

Chitosan is a “natural” insect repellent that is extracted from insect exoskeletons and is permitted for use on both organic farms and conventional farms. When this chemical is applied to a plant, the plant “thinks” it is being attacked by insects and thus produces large quantities of its own natural toxins—such as quercetrin—to ward off the bogus insect invasion. The Japanese publication should not have been included in the Organic Center review because a new variable (chitosan) skewed the results.

For vitamin E, Benbrook and his coauthors reported 14 percent more of this vitamin in organic pears, but it was actually the conventional pears that had 14 percent more vitamin E.

Only eight matches for the antioxidant capacity category were found. Three were described in an article that was not peer-reviewed; another publication had data favorable to the conventional component of the matched pair but was not reported in the Organic Center’s review; and a fifth publication included nutrient content from an inedible portion of a fruit, the peel of a kiwi.

Most egregiously, Benbrook and his coauthors designated nitrate as an “undesirable” nutrient even though new research has demonstrated nitrate is in fact a desirable nutrient.

More Important Differences

While some studies have shown differences in nutrient content between organically and conventionally grown crops, more significant nutrient differences are the result of genetic differences in crop variety, the type of soil in which the crops are grown, the geographic locations of the farms, the year the crops are grown, the amount of water received (rainfall and irrigation), the amount of sunlight the crops were exposed to, and, last but certainly not least, freshness.

Even if organic food advocates should eventually turn out to be correct in their assertions that organic food has higher nutrient content than conventional food when tested in some side-by-side experiments, just how is the consumer going to use this information to make a healthy choice?

Except for just a few fruits and vegetables (apples and oranges come to mind), the consumer cannot tell what variety of a crop is being offered for sale, thus making the selection between organic and conventional produce a crapshoot.

Nor does a consumer know if this has been a good year nutrient-wise for organic or conventional production of a particular fruit or vegetable. (Wine connoisseurs, by contrast, are quite aware of year-to-year differences in wine quality.) What type of soil was that organic broccoli grown in? Was it better for nutrition than the soil in which the conventional broccoli in the next bin was grown? How about the geographic location of each organic and conventional farm? Or the amount of sunlight or water? How long ago did the organic choice leave the farm, compared to the conventional choice?

It is quite apparent that the nutrient content of fruits and vegetables is a lot more complicated than a simple choice between organic and conventional. Consumers should consider the economic motivations of those who would have them believe otherwise.

Joseph D. Rosen is an emeritus professor at Rutgers University’s School of Environmental and Biological Sciences and a scientific advisor to the American Council on Science and Health.

For more information …

For a more detailed analysis of the problems with the Organic Center report, see Joseph Rosen’s full-length report for the American Council on Science and Health: