Sales of organic foods are growing by 10 to 20 percent each year in the United States. More than 10 percent of fruits and vegetables sold are now organic. By any measure, organic foods are starting to enter the mainstream American diet.
And with good reason. Organic produce often has higher levels of potentially healthy compounds. And organic farms may fare better in droughts, don't use synthetic fertilizers that contaminate groundwater, and are more hospitable to critical pollinators like bees and butterflies.
What's more, "the data show that you reduce your exposure to pesticide residues when you buy organic foods," says organics expert Charles Benbrook.
Q: Do organic foods have higher levels of nutrients and phytochemicals?
A: Yes. In about 60 percent of the studies, organic food is higher in some nutrients than conventionally produced food. About 30 to 35 percent of the time, there's no statistical difference, and in 5 to 10 percent of the studies, the nutrient levels are higher in the conventional food. That's based on studies that compare the same varieties of fruits and vegetables grown in similar locations, which is the ideal way to do these comparisons.
In a recent Stanford University review—which claimed that organic produce isn't more nutritious than conventional—only half the studies were done that way.
Q: How much higher are the levels in organic foods?
A: Generally about 5 to 15 percent, but they can be 30 or even 100 percent higher. In a two-year study of tomatoes purchased in Barcelona markets published this spring, organic tomatoes had twice the level of some polyphenols as conventionally grown tomatoes.1 Polyphenols are antioxidants and may be one of the main reasons fruits and vegetables are healthy for us.
Q: Why do organically grown plants have more beneficial compounds?
A: The two key factors are the stronger natural defenses of organic plants and a dilution effect in conventional plants.
Plants in an organic field have to fend off a range of insects, so their natural defense mechanisms are turned on earlier and more fully manifest themselves. As a result, they have higher concentrations of defensive compounds that may keep us healthier.
Q: And the dilution effect?
A: If you keep putting on more and more nitrogen fertilizer the way conventional farms do, you drive yields up and produce bigger plants. But this dilutes the plants' levels of vitamins, minerals, and polyphenols.
For example, in the fall you see beautiful, huge apples in stores that are incredibly juicy and very sweet. Those apples were grown in conventional orchards where farmers have pushed up yields and pushed up sugar concentrations by using a lot of nitrogen and irrigation water.
The trees have to do something with the extra nutrients, and the easiest thing is to convert them into sugars. These apples are juicy and sweet, yes, but the concentration of vitamins, minerals, and phytonutrients in them goes down. That's a classic example of the dilution effect.
Q: Does that affect shelf life?
A: Yes. Take apples. Organic apples store longer, and this has been shown all over the world. It's because they’ve got a higher concentration of antibacterial phenolic acids right under their skin, which helps to retard the growth of molds and bacteria that lead to spoilage.
Conventionally grown apples have diluted levels of these natural antibacterial antioxidants. Plus their extra nitrogen and sugar is exactly what spoilage bacteria and molds need to grow.
Q: What about contaminants that cause food poisoning?
A: Both organic and conventional foods can be a source of food poisoning outbreaks. However, in an organic system, there's a much higher level of microbial biodiversity, so there are more naturally beneficial microbes in the system and soil.
Studies show that when you introduce pathogens into an organic system, they often don't survive very long because the biologically rich community of organisms that's naturally there either competes effectively with them or uses them for lunch.
Q: And in conventional plants?
A: Pesticide use in conventional agriculture tends to reduce microbial biodiversity, both in the soil and on the surfaces of the plant. So when a pathogen does take hold, there's more of an ecological vacuum there, and the pathogen populations can grow.
Most bacteria need nitrogen, and a ready source of nitrogen can fuel spikes in their levels. So in conventional systems that have an excess of nitrogen, there's extra "gas" that can drive up pathogen levels.
Q: Are organic foods pesticide-free?
A: No. Although organic foods are grown without the use of synthetic pesticides, they can pick up traces blown in the air from conventional farms or from water or packing materials in processing plants.
Q: Are pesticide levels on organic produce much lower than on conventional?
A: Yes, but if you measure the difference only in terms of the number of residues found, it's not nearly as dramatic as when you take into account the levels of the pesticides found and how toxic they are.
We developed and computed a Dietary Risk Index, or DRI, for the residues found in conventional versus organic strawberries, apples, grapes, blueberries, nectarines, pears, and peaches grown in the U.S. The conventional fruit's DRI averaged 24, while the organic fruit's DRI was only 3. That's impressive.
Since most consumers first seek out organic food to reduce pesticide risks, this shows that people get what they pay for.
Q: Is imported produce riskier?
A: Yes. One of the big changes in pesticide risk over the past decade is that the difference between domestic and imported produce has grown. When Congress passed the Food Quality Protection Act [FQPA] in 1996, which reformed pesticide use, about three-quarters of the dietary risk from pesticides in the food supply was from fruits and vegetables grown in the United States and one-quarter was from imports.
Now probably 80 percent of the risk is from imports and only about 20 percent is from domestically grown food. Today, the highest-risk fresh fruits and vegetables almost across the board are imported. Consumers are exposed to these mostly from December through April.
Q: Why the change?
A: The Environmental Protection Agency implemented the FQPA mostly by restricting the use of pesticides in the United States. It reduced the numbers and rates of pesticide applications and lengthened the interval between the last application and the harvesting of food.
These changes lowered the dietary risk of domestically produced food, but they had no impact on imports.
Q: How significant are the differences?
A: Some are dramatic. The last time the government analyzed domestic and imported peaches for pesticides was in 2008. If you calculate the DRIs for each sample it tested, 98 of the 100 most risky peach samples were imported from Chile, one was from Argentina, and the other was from the United States. Of the 100 peaches with the lowest DRIs, 99 were grown in the U.S.
So if I were a domestic peach grower and saw peaches high on a dirty dozen list, I would be pretty upset. The EPA, the U.S. Department of Agriculture, and Congress need to start driving down the high-risk residues in imported fruits and vegetables, to at least match the reductions achieved by U.S. growers.
Q: How harmful are the traces of pesticides that are on conventional foods?
A: The evidence now is compelling that low-level exposure to organophosphate insecticides from food and the environment has been contributing to a suite of neurological and developmental problems, such as lost IQ points. These problems can be hard to measure in an individual, but are profound for society as a whole.
Q: How extensive has the impact been?
A: David Bellinger of the Harvard Medical School published an important analysis this spring looking at the risk factors that contribute to lower IQs in children.2 He drew on high-quality studies that looked at medical conditions like preterm birth and pediatric bipolar disorders and at the environmental contaminants lead, mercury, and organophosphate insecticides.
From these studies, he estimated that prenatal exposures to organophosphate insecticides were probably causing a greater loss of IQ points among some U.S. children aged five and younger than anything other than preterm births and lead exposure.
While the risk to a given child is small, the exposure is so widespread that the risk to the population is substantial.
Q: The harm is primarily to children?
A: Pound for pound, children are exposed to more pesticides than adults. And their developing bodies are more sensitive to the adverse effects of pesticides.
That's why pesticide regulation must focus on protecting the developing fetus and protecting children, especially during the first two years of life, but also through adolescence. The brain continues to grow and the nervous system continues to develop throughout the teenage years.
Q: What's the evidence of harm?
A: It's challenging to get proof of harm to children or adults. The most compelling evidence is for chlorpyrifos, an organophosphate insecticide. It's almost certainly the riskiest pesticide to humans that's still widely used on food crops.
In two studies published last year, researchers followed 400 children born around the year 2000 to women living in New York City's low-income neighborhoods.3,4 Some of them lived in public housing projects where exterminators used chlorpyrifos to kill insects in the buildings.
When the women gave birth, the researchers collected umbilical-cord blood or urine to measure how much insecticide the fetuses were exposed to in the womb. They’ve been tracking the children for 10 years now.
Q: What impact did chlorpyrifos have?
A: The kids from mothers with the highest levels of chlorpyrifos or other organophosphates during pregnancy were at greater risk for multiple developmental deficits, including slightly lower IQs when they were six to nine years old.
In a similar study of California farmworkers' families, children of mothers with the highest levels of organophosphates during pregnancy had IQs that were 7 points lower than children of mothers with the lowest levels.5
Q: How is that related to food?
A: A quarter of women of reproductive age in the United States in 2000 had average levels of organophosphates in their bodies comparable to the levels found in the high-exposure group of women in the California farmworker study.6
Since then, the EPA has banned nearly all home uses of chlorpyrifos, and has severely restricted most other uses of organophosphates in homes, other buildings, and urban environments. It now permits their use primarily in agriculture. So most of a woman's exposure now comes from food.
It makes sense when you realize that a person eating 3 or 4 servings of vegetables a day is probably exposed to 3 or 5 or 6 organophosphates on a daily basis. It's easy to understand how pregnant women could have these in their bodies. And very low levels may be harming their children.
Q: Hasn't organophosphate exposure decreased since 2000?
A: The EPA has driven down pesticide levels in domestically grown produce, but much less so in imports. We'll have to wait for the next government survey of our health status and levels of contaminants like chlorpyrifos to determine whether there has been a meaningful decline in residue levels in women.
Q: And eating organic foods would lessen the exposure?
A: Yes. When researchers at Emory University in Atlanta gave children organic fruits and vegetables to eat instead of conventional ones, chlorpyrifos fell to almost undetectable levels in their urine in just five days.7
Many experts are both puzzled and disappointed that the EPA has not acted to end all the uses of chlorpyrifos that lead to residues in food or beverages, given our deepening understanding of the many ways that chlorpyrifos exposures can disrupt normal fetal development, leading to cognitive deficits that could have serious lifelong repercussions.
Q: What about adults?
A: Residues in food rarely are high enough to pose acute risks to healthy adults. The concern for adults is with long-term degenerative diseases such as cancer, heart disease, diabetes, and dementia.
Much of the evidence of harm comes from studies on animals or on farmworkers, their families, and others who face the greatest exposures and the greatest risk. But these studies raise concerns about the rest of us, who are exposed to lower levels.
The evidence was strong enough for the President's Cancer Panel to recommend in 2010 that consumers choose, to the extent possible, food grown without pesticides or chemical fertilizers.8
Q: Are people who eat more fruits and vegetables healthier even if they don't eat organic produce?
A: Yes. That's why the single most important diet change you can make is to eat more fruits and vegetables and less bad fat, added sugar, and highly processed foods. The second most important thing is to seek out organic fruits and vegetables.
Q: How hard would it be to lower the pesticide risks in food?
A: The EPA could reduce by one-half or more the dietary risk in the U.S. food supply by selectively targeting just a few pesticides applied to no more than a dozen crops. Of the 200 pesticides found on our food, just six account for 66 percent of the total risk. One of them is chlorpyrifos.
1 J. Agric. Food Chem. 60: 3373, 2012.
2 Environ. Health Perspect. 120: 501, 2012.
3 Environ. Health Perspect. 119: 1182, 2011.
4 Environ. Health Perspect. 119: 1196, 2011.
5 Environ. Health Perspect. 119: 1189, 2011.
6 Environ. Health Perspect. 113: 1802, 2005.
7 Environ. Health Perspect. 116: 537, 2008.
8 deainfo.nci.nih.gov/advisory/pcp/annualreports/pcp08- 09rpt/PCP_Report_08-09_508.pdf.