‘Natural’ Holiday Foods Are Not Carcinogen-free

Published November 1, 2002

The holiday season is a good time to remember that the American food supply is by far the best in the world—and the best it has been in the history of this country. It is the best not only in terms of its abundance and variety, but also in terms of its safety.

Our diet—like diets around the world—is made up of water, macronutrients (carbohydrates, proteins, and fats), micronutrients (vitamins and minerals), and tens of thousands of other naturally occurring chemicals. A few of these latter chemicals either have been shown to cause cancer in laboratory rodents in research studies or have been shown to be “mutagens” when tested with bacteria. Mutagens, because they can damage DNA—genetic material—are often thought of as “possible animal carcinogens.” Mutagen tests, such as the Ames test, are often used as quick indicators to predict how likely a chemical is to cause cancer.

Back in 1958, when Congress passed legislation (the so-called Delaney amendment to the 1938 Food, Drug and Cosmetics Act) to keep “carcinogens” out of our processed food supply, it was assumed carcinogens (a) were rarely found in foods and (b) were put there by humans, either purposely, through food additives, or inadvertently, in the form of pesticide residues. The Delaney amendment banned from American food any artificial substance that could be shown to cause cancer in lab animals—no matter how small the amount of the substance in a food or how high the dose given to test animals.

Some progress has been made since 1958, however: In 1996 the Food Quality Protection Act removed the scientifically untenable “zero-risk” requirement from the approval process for pesticides. This narrowed the scope of the irrationally restrictive Delaney clause.

Rodent Carcinogens Abound in Nature

In the 40-plus years since Delaney was passed, it has become clear that many naturally occurring chemicals—chemicals that are plentiful in our food supply—cause cancer in rodents when fed in high doses over a lifetime. Furthermore, scientists Bruce N. Ames and Lois Swirsky Gold have analyzed human exposure to chemicals, both natural and man-made (synthetic), that have been classified as “rodent carcinogens.” The researchers have concluded that when ranked on an index (the HERP Index) that compares human exposure to the dose that increases tumors in rodents, the possible cancer hazard to humans from the background of dietary intake of nature’s own rodent carcinogens ranks high in comparison to the possible hazard from residues of synthetic pesticides or additives.

Human dietary intake of nature’s pesticides is about 10,000 times higher than human intake of synthetic pesticides that are rodent carcinogens. In other words, consumers who choose to worry about eating chemicals shown to cause cancer in rodents (and ACSH does not recommend you worry about this hypothetical risk) should understand that the human diet is full of naturally occurring rodent carcinogens.

Present scientific knowledge suggests that residues of synthetic rodent carcinogens in our diet are unlikely to pose a risk of cancer in the quantities we consume on a daily, monthly, or yearly basis. The data are inadequate to allow us to evaluate human risk at low doses, and the uncertainties are enormous.

We hear much about “carcinogens” in our food. But the media use the designation “carcinogen” most frequently in conjunction with man-made rodent carcinogens—substances such as Alar (a fruit-ripening chemical), saccharin (a synthetic, noncaloric sweetener), and BHA (butylated hydroxyanisole, a synthetic antioxidant).

What ACSH demonstrates with its holiday menu is that chemicals that are rodent carcinogens, or are suspected of being such, abound in nature.

Many of these naturally occurring rodent carcinogens are natural pesticides—chemicals that plants produce to repel or kill predators. Of the approximately 10,000 such natural pesticides occurring in the diet, only about 60 have been tested in rodent experiments. These chemicals are found in a wide variety of our food plants: Brussels sprouts, cantaloupe, cauliflower, cherries, chili peppers, cocoa, garlic, grapes, kale, lentils, lettuce, and radishes—to name just a few that are not in our Holiday Menu.

Lab Rat Doses Are Not Human Doses

The consumption of small doses of rodent carcinogens, whether of natural or synthetic origin, is quite unlikely to pose a cancer hazard to humans. When you understand that carcinogens and mutagens are everywhere in Mother Nature’s own food supply, you can see the absurdity of panicking over tiny levels of synthetic chemicals (such as pesticide residues) that are “carcinogens” when fed in large doses over a lifetime to rodents.

If you chose to believe that every rodent carcinogen was also a potential human carcinogen, and if you then chose to extrapolate directly from rodent to human, the background of naturally occurring chemicals that people consume at levels close to the rodent-carcinogenic dose would still cast doubt on the importance for human cancer of synthetic chemical residues.

Note, for example, on the Holiday Menu that the bread in the stuffing contains furfural, a rodent carcinogen. But when you take into account the difference in body weight between a human and a rodent, based on the carcinogenicity data available from the laboratory, a person would have to eat 82,600 slices of bread to consume an amount of furfural equal to the amount that increased the risk of cancer in rodents.

When looking at this example, remember the conditions of the animal studies: Doses are fed every day of the rodent’s life (usually two years). To get an equivalent carcinogenic dose, a human would have to consume those 82,600 slices of bread every day for years.

Too Much of a Good Thing

The primary risk factor in holiday meals—other than the risk of food poisoning from the improper handling or preparation of food—is getting too much of a good thing. A hungry holiday eater can easily consume 2,000-plus calories at one sitting. A consistent intake of excessive calories contributes to obesity, with its attendant higher risk of heart disease. Interestingly, excessive caloric intake has been called the “most striking” carcinogen in rodent carcinogenicity studies. Body weight is a good predictor of a rat’s risk of cancer as shown in comparisons of rats on calorie-restricted diets and rats permitted to eat all they want.

In our quest to reduce our cancer risk by manipulating our diet, we should focus on dietary imbalances in what we eat, not on trace chemicals. Numerous epidemiological studies have indicated that people who consume a diet high in fruits and vegetables have a lower risk for various types of cancer. This is true in spite of the fact that natural chemicals that are also rodent carcinogens occur abundantly in many of these same fruits and vegetables. Note that the populations studied lowered their risks even though their food presumably contained synthetic pesticide residues. High fruit and vegetable consumption was still protective against cancer.

The foods on our Holiday Menu are healthful and wholesome despite the presence in them of some of Mother Nature’s own chemicals that have been shown to be carcinogenic in high-dose rodent tests.