Visit our Re-post guidelines
Organic agriculture is booming. More and more people believe organics are better for our health than conventionally grown fruits and vegetables. But what does the science say?
Researchers from Sweden and Pakistan wanted to know whether organically grown produce was in fact better for human health. They undertook a review of all the studies comparing organically and conventionally grown produce.
The researchers looked at whether organics provide better concentrations of certain nutrients. In particular they focused on vitamin A, carotenoids, iron, zinc, selenium, iodine, vitamin E, and phenolic compounds. Phenols and polyphenols are compounds such as anthocyanins and flavonoids that have antioxidant or other human health benefits.
In their results, published in the International Journal of Environmental Research and Public Health, they found the evidence mixed. Still, they concluded there was "a clear indication of a beneficial effect of organic food/extracts as compared to conventional ones."
Pesticides and Heavy Metal Residues Much Higher in Conventional Produce
Not surprisingly, the researchers found conventional crops contain more pesticide residue. When German researchers screened a collection of food samples they found a total of 361 active pesticide substances. Of the samples, 60.2% had residues of at least one pesticide and 40.7% had residues of more than one. Table grapes showed the highest numbers of different pesticide residues with 23 different chemical substances. In apple, orange and pear samples, 10–12 substances were found.
Studies indicate pesticide residues in the food may contribute to the development of Parkinson's disease, cancer and endocrine disorders.
The evidence was not as strong for heavy metals, but the authors noted a number of studies showing higher levels of heavy metals (especially cadmium) from conventionally grown products than from organic ones.
Organic Fruits And Vegetables Are Higher in Health-Promoting Phenols
When it comes to healthy phenolic compounds in foods, organics clearly beat conventional. Many studies have compared total phenols and individual phenolic compounds in organic and conventional wheat, maize, oats, potatoes, marionberries, strawberries, blueberries, black currant, peach, pear, apple, kiwi, tomatoes, leaf lettuce, collards, and bok choy.
The researchers attributed the higher levels of phenols in organically grown crops to the soil. Organic soils have higher microbial biomass and activity, higher biodiversity and more biogeochemical processes. The higher phenol levels are also related to the plants' defense mechanisms against diseases and pests in the organically grown crops.
When it comes to other nutrients, however, the researchers couldn't find a clear benefit in organics. They found that the genes of a particular plant are just as important as farming practices in determining the nutritional content of a crop. Organic farming is just one element among many farming practices.
When drawing comparisons between two crops, the results are often muddied by different locations, natural soil conditions, irrigation, harvesting conditions, and storage methods.
Many studies have tried to compare levels of iron and zinc in organic versus conventional strawberries, tomatoes, green beans, and wheat. Some studies show higher iron and zinc levels in organics. Others show lower levels. In other words, the study results were too inconclusive to say clearly whether organic or conventional is better when it comes to iron and zinc. They found other factors, like type of crop, year, place, environment, and harvest timing seem to be of higher importance than organic cultivation.
Likewise with carotenoids and vitamin A. Studies have compared organic and conventional farming of wheat, green cauliflower, tomatoes, sweet red bell peppers, grapefruit, grapes, apples and carrots. No significant differences were found. Again, weather, environment and genotype of the crop seem to play a larger role for the carotenoid content than whether the crop is raised organically.
The same was true for vitamin E (tocopherols). Studies have compared organic and conventional wheat, barley, rice, strawberries, peach, pears, plums, olives, sunflower, potatoes, and fava beans. There were no significant differences with a few exceptions. Some tocopherols were higher in organic barley, plums and pears.
Do any of these nutritional differences translate to an actual health effect?
Laboratory Studies Show Health Benefits From Organics
In lab studies, animals fed with organically grown feed had better reproductive performance and immune status, and greater fertility and longevity. Several other animal studies report that animals can discriminate between organic and conventional feed in food preference tests. And they prefer organic produce. To date, there are no good human studies. Short-term intervention studies haven't yet shown any significant difference for people eating conventional or organic food. Still, the researchers concluded that eating organic food seems to be positive from a public health point of view. But they're still not sure why. More studies are needed.
In the meantime, choose organics when you can. And check out the Environmental Working Group's list of the Dirty Dozen Plus fruits and vegetables you should definitely buy organic to reduce your pesticide exposure.