Finding in tomatoes supports generally indications; Organics' nutrition advantages appear minor and should not be consumers' main motivation
by Craig Weatherby
Affirming prior reports, a study published in the respected Journal of Agricultural and Food Chemistry shows that organically grown tomatoes contain higher levels of beneficial flavonoids.
Flavonoids are polyphenol-type antioxidants. They occur in virtually all plant foods and are associated with a range of preventive health benefits.
A team of researchers from the University of California-Davis and the University of Minnesota analyzed the levels of two beneficial flavonoid-type antioxidants—quercetin and kaempferol—in dried tomatoes (Mitchell AE et al 2007).
They found that tomatoes grown by certified-organic methods contained 79 and 97 percent more quercetin and kaempferol respectively, compared with tomatoes grown by conventional methods.
What does this say about the nutritional advantage of organic foods? To find out, let's take a closer look at the new study, and the evidentiary context in which it appears.
Plants produce antioxidant compounds in response to stress
The authors hypothesized that “over-fertilization” of the conventionally grown plants resulted in lower levels of flavonoids, which are produced in response to stresses, including nutrient deficiencies that can make plants more vulnerable to infections and pests.
Levels of the flavonoids in the organically grown plants increased over time as soil levels of nitrogen compounds decreased.
As the researchers put it, “This increase [in flavonoid content] corresponds... with reduced manure application rates once soils in the organic systems had reached equilibrium levels of organic matter” (Mitchell AE et al 2007).
Similarly, researchers at Kansas State University reported in 2005 that organic farming produced higher levels of flavonoid antioxidants as a result of the crops' increased vulnerability to insect attack.
As the Kansas team wrote, “…although organic production method alone did not enhance biosynthesis of phytochemicals [flavonoids] in lettuce and collards, the organic system provided an increased opportunity for insect attack, resulting in a higher level of total phenolic agents [flavonoids]...” (Young JE et al; 2005).
Small nutrition advantage not the primary reason for organics
Prior studies comparing the levels of vitamins, minerals, and antioxidant flavonoids in organic and conventional produce have produced mixed results, although they've generally found higher levels of all three in organic produce.
As the authors of recent literature review reported last year, “Organic crops contain a significantly higher amount of certain antioxidants (vitamin C, polyphenols and flavonoids) and minerals… Moreover, there is a lower level of pesticide residues, nitrate and some heavy metal contaminations in organic crops compared to conventional ones” (Gyorene KG et al 2006).
Studies have also found that organic produce contains higher-quality protein compared with conventional crops, albeit in slightly smaller amounts (Magkos F et al 2003; Worthington V 2001).
To be fair, some of the nutrient-density advantage possessed by organic produce stems from the fact that it typically contains less water per ounce, hence higher levels of dry matter, including nutrients, per ounce (Worthington V 1998; Gyorene KG et al 2006).
(The new study compared nutrient levels in dried tomatoes. so that was not the case in this instance.)
The nutritional advantages of meats and dairy products from grass-fed (not grain-fed) animals over their conventional, grain-fed counterparts are actually clearer than the advantages of products from animals fed organic grains.
Meats and dairy products from grass-fed animals—whether organic or conventionally raised—typically offer a better balance of omega-3 to omega-6 fatty acids, and somewhat less saturated fat.
Organic motivations: purity and eco-protection predominate
When demand for organic foods began to rise dramatically in the late 1980's, their alleged nutritional advantages were not among the main reasons why consumers wanted them… nor was enhanced nutrition a main motivation for farmers who adopted organic methods.
Instead, demand for organic agriculture grew fast for four key reasons:
- Cut use of synthetic pesticides
- Protect groundwater and wildlife
- Raise soil fertility and reduce erosion
- Reduce fossil fuel inputs (petroleum-based fertilizers and pesticides)
Even though crop yields tend to be lower on organic farms, they tend to be as or more financially successful as conventional farms because their overhead, in the form of synthetic pesticides and fertilizers, is far lower.
For example, Swiss researchers compared the effects, over 21 years, of three different agricultural techniques—organic, bio-dynamic, and conventional—on the soils and crops from three fields with similar soil compositions, subjected to identical crop rotation schedules (Mader P et al 2002).
And this is what they found in the organic and bio-dynamic systems, compared with the conventional plots:
- Crop yields were 20% lower
- Pesticide use was reduced by 97%
- Input of fertilizer and energy was reduced by 34 to 53%
As the Swiss authors wrote, “Enhanced soil fertility and higher biodiversity found in organic plots may render these systems less dependent on external inputs” (Mader P et al 2002).
- Caris-Veyrat C, Amiot MJ, Tyssandier V, Grasselly D, Buret M, Mikolajczak M, Guilland JC, Bouteloup-Demange C, Borel P. Influence of organic versus conventional agricultural practice on the antioxidant microconstituent content of tomatoes and derived purees; consequences on antioxidant plasma status in humans. J Agric Food Chem. 2004 Oct 20;52(21):6503-9.
- Chassy AW, Bui L, Renaud EN, Van Horn M, Mitchell AE. Three-year comparison of the content of antioxidant microconstituents and several quality characteristics in organic and conventionally managed tomatoes and bell peppers. J Agric Food Chem. 2006 Oct 18;54(21):8244-52.
- Gyorene KG, Varga A, Lugasi A. [A comparison of chemical composition and nutritional value of organically and conventionally grown plant derived foods] Orv Hetil. 2006 Oct 29;147(43):2081-90. Review. Hungarian.
- Mader P, Fliessbach A, Dubois D, Gunst L, Fried P, Niggli U. Soil fertility and biodiversity in organic farming. Science. 2002 May 31;296(5573):1694-7.
- Magkos F, Arvaniti F, Zampelas A. Organic food: nutritious food or food for thought? A review of the evidence. Int J Food Sci Nutr. 2003 Sep;54(5):357-71. Review.
- Mitchell AE, Hong YJ, Koh E, Barrett DM, Bryant DE, Denison RF, Kaffka S. Ten-year comparison of the influence of organic and conventional crop management practices on the content of flavonoids in tomatoes. J Agric Food Chem. 2007 Jul 25;55(15):6154-9. Epub 2007 Jun 23.
- Worthington V. Effect of agricultural methods on nutritional quality: a comparison of organic with conventional crops. Altern Ther Health Med. 1998 Jan;4(1):58-69. Review.
- Worthington V. Nutritional quality of organic versus conventional fruits, vegetables, and grains. J Altern Complement Med. 2001 Apr;7(2):161-73.
- Young JE, Zhao X, Carey EE, Welti R, Yang SS, Wang W. Phytochemical phenolics in organically grown vegetables. Mol Nutr Food Res. 2005 Dec;49(12):1136-42.