The levels of pesticides that linger on fruits and vegetables are much less of a health threat than eating too little produce, argued a scientist at this week's meeting of the American Chemical Society in Denver.
According to growing evidence, said Bruce Ames, senior scientist at the Children's Hospital Oakland Research Institute in California, even slight nutrient deficiencies can lead to chronic health problems. With less access to affordable produce, low-income populations face the biggest risks.
It's a controversial theory, partly because there are still many unknowns about how the wide variety of chemicals we encounter in our daily lives may affect our health. Some recent studies have also linked certain pesticides with developmental problems in children, though it's still unclear if exposure through food actually contributes much to the problem.
"If you ask the public what is causing cancer, they'll say it's the pesticides on fruits and vegetables, but that's the wrong message to give people," Ames said. "To me, the real risks are eating a bad diet, even if you just take obesity."
As debates continue about the ability of regulators to accurately weigh health risks of chemical exposures, most experts agree that eating fruits and vegetables remains essential, even if consumers can't afford organics.
"Environmentalists hate me because I'm saying everything they've been passionate about for years is wrong," he added. "I think pesticides are good for the environment because you're getting more food out of less land and they're not giving you cancer at the level you're getting them."
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Bruce Ames first made a name for himself in the early 1970s, when he developed a now widely used method -- called the Ames Test -- for assessing the likelihood that chemicals will cause DNA damage, which can lead to cancer. Eventually, he started to question growing concerns about pesticide residues on food.
Every plant, Ames said, is full of 100 or more chemicals, including "natural pesticides," which the plants make to defend themselves against predators. These compounds account for more than 99 percent of the chemicals we consume. And in tests, Ames said, studies show that the natural chemicals have just as much cancer causing potential as synthetic pesticides do.
"When you eat broccoli, you make compounds that work the same as dioxins" and bind the same receptor, Ames said. "When you compare the amounts, it seems like you should worry about broccoli. The whole thing didn't seem plausible."
In rodent studies, he added, the levels of chemicals required to cause cancer are orders of magnitude higher than what regulations allow on produce in the United States. It's not ethical to do the same kinds of experiments on people, so no one knows for sure exactly how pesticides affect human health at various levels. But epidemiological studies that look for correlations have failed to show a link between eating larger portions of conventional produce and higher risks of cancer.
Instead, Ames argued, common nutritional deficiencies are far more likely to accelerate aging and lead to cancers, among other diseases. As an example, he pointed to research that has linked low levels of folic acid with DNA damage. Ten percent of Americans and half of people in the lowest-income brackets, he said, have levels low enough to be concerned about.
According to his Triage Theory of nutrition, when the human body gets low on any of the 30 essential vitamins and minerals, it prioritizes survival by fueling the proteins needed for daily functioning. But the trade-off is a decline in long-term health.
"A focus on nutrition in general would be much more beneficial to human health than this misguided focus on extraordinarily small contamination levels of pesticides," said Samuel Cohen, a pathologist with expertise in toxicology and carcinogenesis at the University of Nebraska Medical Center in Omaha. "Every chemical has toxicity, but it’s all in the dose. The amount of pesticides present as residues on food is miniscule."
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Part of the problem, Cohen said is that analytical chemistry techniques have become so refined that scientists are able to detect much lower levels of chemicals in food and water than they could just a decade ago.
Still, some experts remain cautious. For one thing, the process of setting safe levels for chemicals in the food supply involves just as much policy and art as it does science, said Betsy Wattenberg, a toxicologist at the University of Minnesota, Twin Cities. Of the 80,000 or so chemicals that people are regularly exposed to, she estimated that data on people is available for fewer than 100.
To account for a large number of uncertainties, regulatory agencies build in huge margins of safety. But there is no definitive evidence to say for sure that those levels are safe, especially considering that people are exposed to so many chemicals at the same time.
"It's very rare to have a human study where you can see that this caused that," Wattenberg said. "If you're a person who's eating food and in general, you want to be protected, ideally you wouldn’t want any pesticides in your food because who wants to take that risk? People don’t want to be exposed to something they don't have a choice about."
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Today, some of the biggest concerns surround a class of pesticides called organophosphates, which are designed to attack molecules in the nervous systems of insects. We have similar molecules in our bodies. And three recent studies by three different groups of researchers showed that mothers who are exposed to higher levels of organophosphates while pregnant give birth to children who score lower on intelligence tests at age seven.
The studies relied on blood and urine tests, so no one can say for sure what the major source of exposure was for the women, though researchers suspect that eating produce contributes far less risk than does spraying your home with pesticides or living near agricultural fields.
For now, public health experts continue urge people to eat the recommended two to six and a half cups of fruits and vegetables a day. And since many people can't afford organics, just make sure to wash your produce well, said Kim Harley, an epidemiologist at the University of California, Berkeley.
"We really stress that we don't want people to stop eating fruits and vegetables," Harley said. "We're just saying there are unanswered questions and some concerns about pesticide exposure. There is starting to be evidence that pesticides may impact children’s development, and we need proper risk assessment to answer this question."