DENVER, Aug. 30, 2011 -- The increasingly prevalent notion that expensive organic fruits and vegetables are safer because pesticides -- used to protect traditional crops from insects, thus ensuring high crop yields and making them less expensive -- are a risk for causing cancer has no good scientific support, an authority on the disease said here today. Such unfounded fears could have the unanticipated consequence of keeping healthful fruits and vegetables from those with low incomes.
Bruce N. Ames, Ph.D., developer of a widely used test for potential carcinogens that bears his name, spoke at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held here this week. With more than 7,500 reports on new advances in science and more than 12,000 scientists and others expected in attendance, it will be one of 2011's largest scientific gatherings.
Ames described his "triage theory," which explains how the lack of essential vitamins and minerals from fruit and vegetables in the diet of younger people can set the stage for cancer and other diseases later in life. A professor emeritus of biochemistry and molecular biology at the University of California at Berkeley, Ames also is a senior scientist at Children's Hospital Oakland Research Institute, where he works on healthy aging. He developed the Ames test, which uses bacteria to test whether substances damage the genetic material DNA and, in doing so, have the potential to cause cancer. He has received the U.S. National Medal of Science among many other awards.
In the presentation, Ames said that today's animal cancer studies unfairly label many substances, including pesticides and other synthetic chemicals, as dangerous to humans. Ames' and Lois Swirsky Gold's research indicates that almost all pesticides in the human diet are substances present naturally in plants to protect them from insects.
"Animal cancer tests, which are done at very high doses of synthetic chemicals such as pesticides -- the "maximum tolerated dose" (MTD) -- are being misinterpreted to mean that minuscule doses in the diet are relevant to human cancer. 99.99 percent of the pesticides we eat are naturally present in plants to protect them from insects and other predators. Over half of all chemicals tested, whether natural or synthetic, are carcinogenic in rodent tests," Ames said. He thinks this is due to the high dose itself and is not relevant to low doses.
At very low doses, many of these substances are not of concern to humans, he said. For example, a single cup of coffee contains 15-20 of these natural pesticides and chemicals from roasting that test positive in animal cancer tests, but they are present in very low amounts. Human pesticide consumption from fresh food is even less of a concern, according to Ames -- the amount of pesticide residues that an average person ingests throughout an entire year is even less than the amount of those "harmful" substances in one cup of coffee. In fact, evidence suggests coffee is protective against cancer in humans.
Unfounded fears about the dangers of pesticide residues on fruit and vegetables may stop many consumers from buying these fresh, healthful foods. In response, some stores sell "organic" foods grown without synthetic pesticides, but these foods are much more expensive and out of the reach of low-income populations. As a result, people -- especially those who are poor -- may consume fewer fruits and vegetables.
But how does a lack of fresh produce lead to cancer and other aging diseases? That's where Ames' triage theory comes in.
In wartime, battlefield doctors with limited supplies and time do a triage, making quick decisions about which injured soldiers to treat. In a similar way, the body makes decisions about how to ration vital nutrients while experiencing an immediate moderate deficiency, but this is often at a cost.
"The theory is that, as a result of recurrent shortages of vitamins and minerals during evolution, natural selection developed a metabolic rebalancing response to shortage," he said. "Rebalancing favors vitamin- and mineral-dependent proteins needed for short-term survival and reproduction while starving those proteins only required for long-term health." Ames noted that the theory is strongly supported by recent work (Am J Clin Nutr. DOI: 10.3945/ajcn.2009.27930; FASEB J DOI:10.1096/fj.11-180885; J Nucleic Acids DOI:10.4061/2010/725071).
For example, if a person's diet is low in calcium -- a nutrient essential for many ongoing cellular processes -- the body takes it from wherever it can find it -- usually the bones. The body doesn't care about the risk of osteoporosis 30 or 40 years in the future (long-term health) when it is faced with an emergency right now (short-term survival). Thus, insidious or hidden damage happens to organs and DNA whenever a person is lacking vitamins or minerals, and this eventually leads to aging-related diseases, such as dementia, osteoporosis, heart trouble and cancer.
And with today's obesity epidemic, resulting largely from bad diets that lack healthful foods containing vitamins, minerals and fiber, aging-related diseases are likely to be around for some time to come.
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Most of the world's population, even in developed countries, has inadequate intake of one or more of the ~30 essential vitamins and minerals (V/M) that a varied and balanced diet should provide. Triage theory (PNAS 2006 103;17589) posits that, as a result of recurrent shortages of V/M during evolution, natural selection developed a metabolic rebalancing response to shortage. The rebalancing favors V/M-dependent proteins needed for short-term survival and reproduction while starving those proteins only required for long-term health. Triage theory predicts that the consequence of moderate shortages of even a single V/M, though insufficient to cause overt clinical symptoms, will impair functions essential for long-term health. This impairment will result in insidious damage (e.g. increased DNA damage) that, over time, leads to the acceleration of age-associated diseases (e.g. increased cancer). Analyses (AJCN 2009 90;889, J Nucleic Acid 2010 doi:10.4061/2010/ 725071, FASEB J 2011 doi:10.1096/fj.11-180885) show that a triage perspective is both correct and useful.
Animal cancer tests, which are done at the maximum tolerated dose (MTD), are being misinterpreted to mean that minuscule doses of synthetic chemicals such as pesticides are relevant to human cancer. 99.99% of the pesticides we eat are naturally present in plants to ward off insects and other predators. Over half of all chemicals tested, whether natural or synthetic, are carcinogenic in rodent tests (Handbook of Pesticide Toxicology 2001, 799-843). A plausible explanation is that the MTD causes chronic cell killing and consequent cell replacement, a risk factor for cancer that can be limited to high doses. Reducing our exposure to traces of dietary synthetic pesticides is expensive and will not plausibly reduce cancer rates. Fruits and vegetables are effective dietary sources of V/M, and making them more expensive, e.g. organic food, could increase cancer in the poor.