This summer saw the publication of a study of the nutritional value of organic versus conventional foods by scientists with the London School of Hygiene and Tropical Medicine. Based on a review of 55 articles they judged of satisfactory quality, the scientists, led by Alan Dangour and funded by the governmental Food Safety Agency, concluded that “there is no evidence of a difference in nutrient quality between organically and conventionally produced foodstuffs.”

Preston Andrews, WSU professor of horticulture and a prominent researcher of nutrient value of organically grown food, is irked by the report, published in the American Journal of Clinical Nutrition, both by its conclusion and its methods.

For one thing, says Andrews, “They don’t understand field research.” Back to this in a moment.

basket of vegetables
Is organically raised food nutritionally superior? As they say, more study is needed. (Photo Robert Hubner)

In spite of the icy response to the report by a good many others than Andrews, a close reading of the article and its allowances detracts somewhat from its conclusiveness.

Dangour and his colleagues write, “We did not address differences in contaminant contents (e.g., herbicide, pesticide, or fungicide residues) or the possible environmental consequences of organic and conventional agricultural practices because that was beyond the scope of our review.”

Given that these factors have been the main focus of many of conventional agriculture’s critics, one might shrug off the impact of the paper.

However, the “nutrient density” of organically produced food has been actively promoted by its proponents, including Andrews and other participants in the Organic Center, which supports some of Andrews’s work. The Organic Center’s mission is “To generate credible, peer-reviewed scientific information and communicate the verifiable benefits of organic farming and products to society.”

In a report similar in scope to the FSA report (though not peer-reviewed), the Organic Center last year assessed 236 “matched pairs” of measurements including an organic and a conventional sample of food in 97 published studies. Andrews was an author of the report along with WSU associate professor of pharmacy Neal Davies, WSU pharmacology and toxicology doctoral student Jaime Yáñez, and other Organic Center scientists.

The Organic Center study found that organic foods were more nutritionally dense in 61 percent of the cases. The conventional foods were more nutritionally dense in 37 percent of the cases. The study considered these nutrients: four measures of antioxidants, three precursors of key vitamins (A, C, and E), potassium, phosphorus, nitrates, and total protein.

In three-quarters of the cases, the organic foods contained higher levels of phytonutrients, including antioxidants and polyphenols.

The FSA study identified 162 studies, 55 of which they considered of satisfactory quality. Their analysis found that conventionally produced crops had a higher content of nitrogen, and organic crops had significantly higher content of phosphorus and titratable acidity. They found no evidence of a difference in the other eight nutrients considered: vitamin C, phenolic compounds, magnesium, calcium, potassium, zinc, total soluble solids, and copper.

Organic Center scientists faulted the FSA study for actually identifying significant differences, then dismissing them. For example, Dangour and his colleagues found conventional foods to contain higher nitrates, which are widely considered a potential health hazard.

They also criticized the FSA for omitting measures of some important nutrients, including total antioxidant capacity.

But the main problem with the FSA report, says Andrews, was their screening methods, in part due to the absence of matched pairs.

All that the FSA study required was that the varieties of food crops or animals had to be named, but not be the same, says Andrews. Different varieties of the same crop can vary wildly in their nutrient levels.

Likewise, matching soils were not required in the FSA study, nor was proximity.

The Organic Center study required that identical varieties grown on identical soils in close proximity be compared.

If the contending studies prove anything, it’s that such a study is difficult at best. According to Andrews, “The claims of health benefits for organic foods are difficult to make conclusively because so few studies have tested the question directly.”

As far as he knows, there has never been a long-term epidemiological study of the health effects of eating organic versus conventional food.

It could be argued that nutrition is a moot point, at least in a society in which, on the one hand, food is plentiful, and on the other, the price of organically raised food places it beyond the reach of those who could most use the increased nutrition.

Michelle McGuire, a nutrition scientist at WSU, is a spokesperson for the American Society for Nutrition, which publishes the American Journal of Clinical Nutrition, and wrote the press release regarding the FSA study. She notes that we have solid data on only a handful of the hundreds of nutrients in our food.

Referring to the Dangour study, she says,“I don’t use that study as evidence that organics aren’t more nutritious; it’s evidence that we don’t have evidence that they are. We really don’t know that much, yet.”

McGuire does say that she often buys organically grown food, not because she’s particularly concerned about nutrient content, but because it tastes better.

Andrews in fact led one of the few studies that has attempted to measure the sensory factor. In a study published in Nature, he and colleagues used blind taste tests which found that organic Golden Delicious apples were sweeter and less tart, especially after long-term storage. A continuation of that study, published in HortScience, found that consumers rated organic Gala apples firmer and with better texture and flavor than conventional Galas.