What Are the Benefits of Organic Food?

A recent study from Stanford University looked at 17 studies comparing people who ate organic or conventional diets, and 223 studies comparing the bacterial, fungal or pesticide contamination of such foods. There were no long-term studies of health outcomes between the two diets in their analysis. The studies showed no consistent differences in the vitamin content of organic products, although there were higher levels of omega-3 fatty acids in organic milk. The study did find that organic produce had a 30% lower risk of pesticide contamination, but the pesticide levels in all food generally fell within the allowable safety limits. They found that children on organic diets had lower levels of pesticide residues in their urine, and organic chicken and pork reduced exposure to antibiotic resistant bacteria, but the clinical significance of all these findings were found to be unclear.

Many people have been confused by these findings from Stanford. Is organic food worth the extra money? Charles Benbrook, a professor at Washington State University’s Center for Sustaining Agriculture and Natural Resources, wrote a compelling answer in the October issue of Nutrition Action Healthletter. Benbrook has worked for the National Academy of Sciences, and consults for The Organic Center. He says that 60% of studies do show a higher nutrient content in organic foods, especially when the comparison is between fruits and vegetable grown in similar locations. The Stanford study did not consistently make such comparisons.

A recent study of tomatoes in Spain showed that organic tomatoes had twice the antioxidant levels as conventional tomatoes. There are two reasons for this. Organic plants have to fend off a range of insects, so they develop more defensive compounds that also keep us healthy. Conventional crops are produced with large amounts of nitrogen fertilizer, which drives up yields and fruit or leaf size, but dilutes the levels of vitamins, minerals and antioxidants.

Contaminants that cause food poisoning can grow more readily in conventional fields, because of extra nitrogen, and the lesser microbial diversity due to pesticide use. In organic fields there is more microbial biodiversity, so pathogens may not last as long or become as numerous.

Organic foods may not be pesticide free, because of traces blown in from conventional fields. However, pesticide levels are markedly lower. Benbrook has devised a scoring system, the Dietary Risk Index (DRI) that measures the number of different pesticide residues and their levels. Looking at organic versus conventional strawberries, blueberries, apples, grapes, nectarines, peaches and pears grown in the US, the DRI was 3 for organics, versus 24 for conventional fruits. Imported conventional fruits from Chile and Argentina have much higher DRIs than those grown in the US, because of more stringent regulations of pesticide use in the US.

According to Professor Benbrook, there is compelling evidence that low level exposure to organophosphate insecticides in food are contributing to neurologic and developmental problems in children, such as lowered IQ. Lead exposure was found to be most harmful in a Harvard study, followed by organophosphate pesticides and methylmercury. The most compelling evidence of harm comes from the insecticide chlorpyrifos, which has been banned by the EPA for home use, but is still permitted in agriculture. Its level in pregnant farmworkers correlated with lower IQs in their children. When researchers at Emory University in Atlanta gave children organic fruits and vegetables, chlorpyrifos levels fell to almost undetectable levels in their urine in 5 days. Chlorpyrifos is made by Dow Chemical. A coalition of farmworker and advocacy groups filed a lawsuit against the EPA in 2007 seeking to ban the use of chlorpyrifos; the suit is still pending.

Professor Benbrook thinks that the most important dietary change we can make is to eat more fruits and vegetables, and less bad fat, added sugar and processed food. I’m going to add – eat with the seasons, so that you avoid imported produce with its higher levels of pesticides. The second most important is – of course - to eat organic produce and organic grains. If you can afford it, this is your most important step.

Subscribe to the Nutrition Action Healthletter if you want to keep up with the science of nutrition in an easy, readable format. It’s easy to find the address on-line, and 10 issues cost only $10!

Finally – let always give thanks to our local organic farmers, and to the Bolinas People’s store with its daily array of luscious, healthy food!

Sadja Greenwood MD back issues at on this blog