Sunday, February 19, 2012 at 10:12PM
Gary Leavitt

Numerous published data sets suggest that consumers may also be justified in assuming that organic produce is more nutritious than conventionally grown produce. However, because of the large number of variables involved and the consequent large scatter in the data, it is not yet possible to draw firm conclusions. Nutrients in fruits and vegetables vary with plant variety, soil type, microclimate, time since harvest, and post-harvest handling. If any of these variables differs for a given comparison, interpretation of nutrient differences is open to question. Hence the Organic Farming Research Foundation states on its web site that "the definitive study has not been done."

While the definitive study may not have been done, there have been many suggestive studies. One of the best was reported in the Journal of Alternative and Complimentary Medicine, in a paper by Virginia Worthington entitled "Nutritional Quality of Organic Versus Conventional Fruits, Vegetables and Grains." This paper is an extension of Worthington's doctoral dissertation at Johns Hopkins University. Her conclusion was that "There appearto be genuine differences in the nutrient content of organic and conventional crops." We now present a few key results from Worthington's paper that expand on this conclusion.

Worthington analyzed measurements reported primarily by other investigators. She had concluded that uncontrolled differences in growing conditions and consequent large scatter in reported data made it impossible to draw confident conclusions. Consequently, she collected all available data and performed statistical analyses to find significant trends. In all, she used data of 41 different studies—including one of her own: Comprising 1240 comparisons. Each comparison involved measuring a single nutrient in an organic fruit, vegetable or grain and comparing with the same nutrient in a conventional fruit, vegetable or grain of the same variety grown in the same season.

The 41 studies investigated differences in 21 nutrient minerals, four heavy metals, eight vitamins, nitrates, and protein quality. Of these, only 12 nutrients were measured often enough to permit statistical analysis. Worthington applied a standard test for statistical significance to these 12 and found that measurements on only four nutrients and one toxic substance passed the test. That is, the measured differences between organic and conventional were not statistically significant except for the five substances. The five substances that passed the test were vitamin C, iron, magnesium, phosphorus and nitrates. The first four are desirable nutrients, while nitrates are undesirable.

Worthington's results for these five prove that organic produce on average has significantly more of the desirable nutrients and less of the toxic nitrates, a result very favorable for the organic side.

However, her results showed a large scatter in the individual comparisons. For example, although 83 comparisons showed more vitamin C in the organic food than in the conventional food, 38 showed less and 11 showed no difference. From these discrepancies one can get an idea of how difficult it would be to confidently conclude from the raw data that organic is always better than conventional. Worthington's statistical treatment increases the confidence level but still leaves a nagging uncertainty. Without more definitive measurements it won't be possible to completely dispel the uncertainty.

Despite uncertainties from the large scatter in the comparison data, all measurements indicated that on average organic food has more of the desirable nutrients and less of the undesirable than conventional food. Even though the statistical treatment was unable to confer significance on differences measured for the other nutrients, all the simple averages nevertheless favored organic over conventional. Specifically, the content of all 21 desirable minerals was higher in organic food than in conventional, and organic crops had lower amounts of heavy metals more often than their conventional counterparts. While the amount of protein in organic food was less than in conventional food, the quality of the protein in terms of desirable amino acids was better in the organic food.

Worthington noted that several of the findings make sense in terms of what we know about plants and their responses to soil minerals. Synthetic fertilizers tend to inundate root zones with excess plant nutrients, while organic methods provide a more continuous supply at lower levels. With excess nitrogen a plant is likely to increase nitrate and protein production and reduce carbohydrate production. Vitamin C is made from carbohydrates, so reduced concentrations of carbohydrates will curtail synthesis of vitamin C. Also, potassium fertilizer can reduce the magnesium content and indirectly the phosphorus content of at least some plants.

Overall the data strongly suggest that Organic crops have better nutrients than conventional crops, but we need that definitive experiment before we dare crow too loudly!

Article originally appeared on Growing for the future! (
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