Carcinogens au naturel?
Meet Robert J. Scheuplein, a senior toxicologist with the Food and Drug Administration, the agency charged with protecting our food supply from dangerous substances ... including pesticides. Scheuplein recently made headlines when he said that the risk from "natural carcinogens" in the food we eat overwhelms the cancer risk from additives, pesticides, and contaminants. Vegetables, grains, spices, even herbal teas-they're all loaded with chemicals that initiate the cancer process, says Scheuplein, who adds that lowering the risk from these carcinogens "would probably be enormously more useful to human health than... eliminating traces of pesticide residues or contaminants." Is he right?
Like dozens of newspapers across the country, the St. Louis Post-Dispatch carried an article last February 20 by the Associated Press.
"Natural carcinogens in meat, grain and other foods," it read, "are a far greater danger than pesticides and additives, accounting for more than 98 percent of the cancer risk in the diet, a government scientist said Monday." That scientist was Robert J. Scheuplein, who directs the FDA's Office of Toxicological Sciences at its Center for Food Safety and Applied Nutrition. Scheuplein was addressing a meeting of the American Association for the Advancement of Science (AAAS).
Are pesticides, contaminants, and additives really insignificant compared to natural carcinogens? Probably not, despite what Scheuplein would have you believe.
And what about fat? Doesn't it play a role in the development of cancer?
Even Scheuplein thinks so. But he limited his analysis to substances that initiate, rather than promote the cancer process (as fat apparently does). Unfortunately, he never bothered to correct the newspapers when they blamed 98 percent of the cancer risk in the diet on natural carcinogens alone. Oops.
Another thing: Just because some isolated chemicals in our foods may cause cancer, there is no evidence that the foods themselves do. In fact, there is overwhelming data that eating a diet rich in vegetables, whole grains, and fruits-many of which contain so-called "natural carcinogens"-can actually protect us from the disease. Scheuplein took an estimate of the risk of getting cancer from diet, and tried to see how much of that risk comes from carcinogens that occur naturally" in our food, and how much comes from synthetic chemicals like pesticides or animal drugs.
His conclusion: the risk from natural carcinogens is 10,000 times greater than the risk from pesticides or animal drugs. How did he come up with this number? By making three outrageous assumptions: * Assumption: We get 10,000 times more carcinogens from food than from pesticides or animal drugs. When people hear Scheuplein's estimates, they assume that he added up the risk of each natural carcinogen in one column and of each man-made carcinogen in another. Not true. He simply guessed that one-tenth of one percent of the 2.2 pounds of food we eat each day are natural carcinogens.
He had to guess, because nobody has a clue what the real percentage is. Even Scheuplein readily admits that "there is virtually no database worthy of the name on the daily intake of natural carcinogens."
Had he assumed that our intake was one-thousandth rather than one-tenth of one percent, for example, he would have concluded that pesticides and natural carcinogens in food pose the same cancer risk. * Assumption: No substances that are intentionally added to our food cause cancer. What about the artificial sweetener saccharin or the food dye Red 3, which even Scheuplein acknowledges cause cancer in laboratory animals? He doesn't factor them into his calculations.
He also ignores other additives like the preservative BHA or the dye Citrus Red 2, even though there is "sufficient" evidence in animals to label them "possibly" carcinogenic to humans, according to the International Agency for Research on Cancer (IARC).
(IARC rates substances as definitely, "probably," possibly," or "probably not" carcinogenic to humans-or as "not classifiable"-Depending on how good the evidence is.) n Assumption: All carcinogens have the same potency. Scientists know for a fact that this isn't true. Even Scheuplein admits that his assumption could introduce a "significant error." So he made a second calculation, this time assuming that natural carcinogens are a hundred times less powerful than pesticides or animal drugs. But he continued to insist that we eat 10,000 times more natural carcinogens than pesticides.
Not surprisingly, his second calculation still showed that we face a greater risk from natural carcinogens. Aren't statistics wonderful? Scheuplein claims that "ordinary" foods are loaded with natural carcinogens. Which foodsand which carcinogensis he talking about? Here are his examples: * Coltsfoot. Not exactly an "ordinary" food in most kitchens, although it is occasionally sold as an herbal tea. IARC says that the evidence is too limited to consider the petasitenine in coltsfoot even "possibly" carcinogenic. * Comfrey. The symphytine in comfrey tea isn't even "possibly" carcinogenic, says IARC. * Bracken fern. It's apparently sold as a salad green, but have you ever seen it? LARC considers it possibly" carcinogenic to humans, so keep any encounters to a minimum. * Cycads. You cycad fans can relax: properly washing cycad nuts removes the "possibly" carcinogenic cycasin. (Of course, if you don't live in the tropics, chances are you'll never run into a cycad.) * Ragwort or groundsel (Senecio) and rattlebox (Crotolaria). These plants contain pyrrolizidine alkaloids, some of which are suspected carcinogens. But they are mostly used as medicinal herbs in Africa, Asia, or Europe. A few species are found as weeds in the U.S. * Garlic, horseradish, and mustard. These contain allyl isothiocyanate, which doesn't even rate as "possibly carcinogenic, according to [ARC. * Mushrooms. Common store-bought white mushrooms (Agaricus bisporus) contain a chemical called agaritine. While IARC says it's not even possibly" carcinogenic, there is "limited" evidence that two of the substances agaritine breaks down into cause cancer in laboratory animals.
"Washing reduces the levels of agaritine and its breakdown products," says Devra Lee Davis, of the National Academy of Sciences, who adds that cooking destroys them both.
There is better evidence that several chemicals in a MAID mushroom, the false morel, are carcinogenic. So, to play it safe, keep your false-morel foraging to a minimum, and make sure you cook them. * Celery, parsnips, and parsley. IARC says there is "sufficient" evidence to call a chemical in these vegetables, 5methoxypsoralen, "probably" carcinogenic, but only when applied to the skin of laboratory animals in the presence of sunlight. Studies were "inadequate" to determine if the chemical causes cancer when eaten.
So go ahead and enjoy-just don't get kinky math them. * Spinach, beets, lettuce, radishes. These also appear on Scheuplein's list, since they contain nitrate. Nitrate doesn't cause cancer, but it can slowly convert to nitrite, which reacts with other substances in food or in the stomach to form carcinogenic nitrosamines.
Fortunately, the fiber and anticarcinogens like vitamin C in these vegetables seem to counter the risk posed by the nitrate. It's also comforting to know that the types of cancers that are linked to nitrosamines are either declining (stomach) or uncommon esophagal) in the United States. * Fish and shellfish. Scheuplein includes fish and shellfish, since they feed on plankton, which may contain cancer-causing polyaromatic hydrocarbons (PAHs).
But most of the PAHs in seafood are created when we smoke or grill it. [see Jul./Aug. 1989 NAH] It's hardly fair to call these PAHs "natural." (1) * Oranges. A chemical found in the peel of oranges and other citrus fruits (d-limonene), although not evaluated by IARC, showed "clear evidence" of cancer in one study of male rats, but "no evidence" in other studies of mice and female rats. (2) In yet another study, d-limonene acted as an anticarcinogen, inhibiting the formation of tumors in mice. (3) * Hot peppers. Like d-limonene in orange oil, capsaicin (which makes hot peppers hot) has not been evaluated by IARC, but shows both cancercausing and cancer-inhibiting properties.(4)
CLEARING THE SMOKE In his zeal to play up the importance of natural carcinogens in the diet and to minimize the risks from pesticides, Scheuplein encouraged (or at least didn't protest against) newspaper articles that contained some misleadingand potentially dangerous-messages: * A day's protein is more damaging to the genes than five cigarettes. Scheuplein is talking about genetic damage to bacteria, not to people. And tests on bacteria are nothing but a crude indicator of a substance's cancer-causing potential in humans.
But why rely on bacteria when there are mountains of human evidence that cigarettes-and not protein-cause more than 100,000 cancer deaths in the United States each year? * Hazardous urethane ... is in beer, yogurt, bread, and other food. True, but the amount in those products is minuscule compared to how much is in many bourbons, European fruit brandies, cream sherries, port wines, Japanese sakes, and Chinese wines.
That's why we petitioned the FDA to test alcoholic beverages and to recall those that are highly contaminated. (Our petition was denied, although the FDA is prodding the booze industry to lower urethane levels.)
UP THE ANTI'S Although there is not enough evidence now, Scheuplein may turn out to be right: many natural chemicals in foods may be carcinogenic. But does that mean that eating the foods they are in increases your risk of cancer?
In most instances, probably not. That's because other naturally occurring substances, called anticarcinogens, may protect us against cancer. Betacarotene, as well as chemicals with nasty-sounding names like phenethyl isothiocyanate (PEITC), found in cauliflower and broccoli, and ellagic acid, found in strawberries and other fruits and vegetables, may help defend our bodies against carcinogens.
"Parsley, sage, rosemary, and thyme not only made a great song," says the National Academy of Sciences' Devra Lee Davis. "They also prevent some toxic [and potentially cancer- causing] molds from growing.
"Garlic and onions, turmeric, cumin, clove, caraway, and seafood all contain substances shown to reduce the effect of cancer-causing agents," she adds.
Davis argues that one of the reasons stomach cancer rates in developed countries are declining may be that we now eat, year-round, fruits and vegetables that contain anti- carcinogens. She calls the decline in stomach cancer "the strongest evidence that natural carcinogens are not likely to play a major role in causing cancer in the United States."
Clearly, more research is needed to understand the net effect of the natural carcinogens and anticarcinogens, as well as the fat, fiber, and other substances in our foods.
Who knows? In five years we may be telling you to avoid parsnips. But for now, there's plenty of evidence that diet is your best defense against cancer other than quitting smoking.
Most experts, including the Surgeon General, the National Academy of Sciences, the National Cancer Institute, and even Scheuplein, agree that to curb our risk of cancer (as well as heart disease), we should be eating more fruits and vegetables-natural carcinogens and all-and less fat.
DOUBLE STANDARD? It's clear that Scheuplein grossly overestimates the importance of "natural" carcinogens, and that he uses that overestimate to persuade us to not worry about the "unnatural" ones-the chemicals that we spray, sprinkle, or let seep into our food.
Don't fall for it. * Additives. Most food additives don't cause cancer, and are safe. But some, like saccharin and BHA, have been linked to the disease. Also, artificial colors should be avoided because their safety hasn't been clearly established.
True, IARC says that there's not enough evidence to call most artificial colors even "possibly" carcinogenicwhich is just what it said about almost all of Scheuplein's natural carcinogens. So aren't we using a double standard when we tell you to eat vegetables and to avoid artificial colors?
You bet we are. Artificial colors are frivolously added to junk foods that have little nutritional value, while vegetables are critical to a healthy diet. * Pesticides. Many industry groups (as well as the FDA) argue that the tiny amounts of pesticides on foods pose no risk.(5) We wish that were true.
It is true that consumers are in far less danger than the people who make, mix, or apply pesticides. It's also true that eating too much fat or too few vegetables probably puts you more at risk than ingesting pesticide residues. But they are still worth worrying about.
The Environmental Protection Agency (EPA) ranks pesticides as the third most important cancer risk it regulates. Only worker exposure to chemicals and indoor radon are more significant.
What's more, we can do something about pesticides.
"Why not put our efforts into controlling those risks-like pesticidesthat we can control?" asks Judy Bellin, a retired EPA senior toxicologist.
But don't we need pesticides?
"Even though American farmers use over thirty times more pesticides today than in 1945," says Edward Groth III, of Consumers Union, "the portion of the harvest that is lost to pests has increased by 20 percent."
HEY YOU ... EAT YOUR VEGGIES Scheuplein is right that more research is needed to help understand the link between diet and cancer. Hopefully, new studies \,Vill someday yield more specific advice on how to avoid cancer through diet.
But for now, let's not explain away the risks of pesticides, additives, and contaminants in our food by pointing a finger at cycad nuts and mushrooms. Let's avoid the risks we can.
In other words: FDA, do your job. And you ... eat your vegetables. [sup. 1] Toxicol. Environ. Chem. 7:297, 1984. [sup. 2] Nat. Toxicol. Prog., Tech. Report 347, 1990. [sup. 3]I Cancer Res. 49: 2689, 1989. [sup. 4] Anticancer Res. 4: 117, 1984. [sp. 5] Food Marketing Institute, with FDA. A Consumer Guide to Food Quality and Safe Handling: Produce and Pesticides," 1989.
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|Title Annotation:||claims that natural carcinogens outweigh the risks from pesticides|
|Author:||Lefferts, Lisa Y.|
|Publication:||Nutrition Action Healthletter|
|Date:||Jul 1, 1990|
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