Dispelling Myths about the Chemical/Cancer Connection

 Dispelling Myths about
the Chemical/Cancer Connection
July 1996 -- Perspectives

By: Andrea Horwich Allen
Contributing Editor

  You've probably known it all along. Nutritionists and health professionals have been trying to get the message across for years. Now one of the most respected scientific organizations in the world has confirmed it: It's far better to eat your fruits and vegetables than to steer clear because you're afraid of pesticides.  A new report from the National Research Council (NRC), a branch of the National Academy of Sciences, addresses this very issue -- one that has grabbed some of the biggest headlines in recent memory: Do the chemicals in our food supply cause cancer?  One conclusion is certain to surprise many chemo-phobic consumers: Naturally occurring dietary chemicals are more carcinogenic than the synthetic pesticides or additives they tend to fear.  A second conclusion will be equally unexpected among certain quarters: Based on what scientists know now, the risk posed by either group of chemicals pales in comparison to the risk of a diet too high in fat and too low in fiber -- in other words, the risk posed by the typical U.S. consumer's diet.Viewing the dietary picture  The report, "Carcinogens and Anticarcinogens in the Human Diet: A Comparison of Naturally Occurring and Synthetic Substances," states: "Toxic chemicals that occur naturally in foods may pose a greater risk of causing cancer than the residues of synthetic pesticides that people consume in their diet. But the danger of either group of chemicals causing cancer is much smaller than the risk associated with diets containing too much fat, too many calories or an excess of alcohol."  Ronald Estabrook, Ph.D., biochemistry professor at the University of Texas Southwestern Medical Center, Dallas, chaired the NRC committee that produced the report. He told the UT Center for Human Nutrition Newsletter that "while some chemicals in the diet do have the ability to cause cancer, they appear to be a threat only when they are present in foods that form an unusually large part of the diet.  "The varied and balanced diet needed for good nutrition -- including fruits and vegetables -- seems to provide significant protection from the natural toxicants in our food," Estabrook adds.  According to Estabrook, the 20-member committee appointed to take on this task studied about 280 chemicals, both natural and synthetic, over a period of 2-1/2 years. They found a wide range of potencies -- although whether or not a chemical occurred naturally was not a factor.  Equally significant was the committee's finding that the mechanisms by which the chemicals worked was not influenced by its natural or synthetic status. "We concluded that a chemical is a chemical, whether it's synthetic or not," Estabrook says.  A particularly intriguing finding was that concentrations of synthetic chemicals, such as pesticide residues, actually are very low in the average diet. That conclusion is especially timely this year because there has been so much discussion in Washington regarding modifying or even eliminating the Delaney Clause.  Until 1992, the U.S. Environmental Protection Agency had been operating more on a "negligible risk" basis, despite the zero-tolerance policy set forth by Delaney. The EPA recently moved to cancel tolerances on numerous pesticides, under a 1992 court order to enforce the regulation as written.  According to groups such as the National Food Processors Assoc., such cancellations are unnecessary even under current regulations -- and would be moot if the Delaney Clause were reformed.  If that happened, consumer fears about pesticides in the food supply would certainly be stoked. Could this new report help put those fears to rest?  The fact that the report was issued by such a widely respected agency should carry some weight. "It's very helpful to have as balanced an organization as the National Academy of Sciences put (the issue) into perspective," notes Joyce Nettleton, D.Sc., director of science communications at the Institute of Food Technologists.The message on the myth  Depending on how thoroughly this report is covered in the consumer media, it could be helpful in dispelling one myth. "There is a widespread perception that synthetic chemicals are killing us and that we're eating tons of them," Nettleton says. The NAS report makes a strong case that our food supply is far from saturated with synthetic chemicals -- and that naturally occurring substances can be just as safe or just as damaging.  A larger question, though, is exactly what role diet plays in causing cancer. That's one that no single report can answer definitively -- much less address all the theories afloat in the consumer media. "Some questions we don't have answers to," Nettleton notes.  "We don't know what causes cancer, aside from tobacco," she adds. "It's tempting to say that it's something in the food supply. Maybe it is, and maybe it isn't."  According to Estabrook, researchers currently attribute about 30% of cancers to diet -- about the same percentage as can be attributed to smoking. Clearly, much is at stake in the quest to determine how diet and cancer are linked, but the researchers were unable to point their collective finger at any specific chemicals.  "Of that 30%, if we say that very little can be attributed to specific chemicals, then what is the cause?" Estabrook asks. "The only other thing we could come up with was (excess) calories and fat."  As the NAS report concluded, there are some naturally occurring chemicals in foods that induce tumors when fed to rats in very high doses. Also, epidemiological studies have shown that some chemicals have been associated with increased risk of cancer in humans. Still, the presence of these chemicals in the average human diet is very small -- and the researchers concluded that the cancer risk posed by these chemicals probably also is very small.Beyond the chemical connection  The role of macronutrients in either causing or fighting cancer is better understood. Excessive caloric intake has been shown to induce tumors in rats, and numerous studies have linked excess fat consumption to increased risk in animals and humans.  On the flip side, diets high in fruits, vegetables and fiber have been shown, in animal and epidemiological studies, to protect against certain cancers. The mechanisms by which they may do so are not yet understood, but this has become one of the hottest areas of nutrition research in years.  In particular, the phytochemicals found in fruits and vegetables are the subject of innumerable studies investigating their potential cancer-fighting properties. Broccoli, for one, has an especially large complement of phytochemicals that are thought to be beneficial -- yet it also contains nitrates.  This chemical profile illustrates the difficulties of trying to link specific foods, or chemicals in the food supply, with cancer. As Nettleton points out, the nitrates found in food sources such as broccoli can be converted by the body to nitrosamines, which are carcinogenic. Vitamin C can help prevent this conversion, she adds, and broccoli just happens to be rich in that vitamin.  Just about the only dietary chemical that the NAS committee thought was definitively linked to an increased cancer risk was the fungus aflatoxin, which is most commonly associated with peanuts. Even this, however, was not considered a "natural" chemical because it doesn't occur naturally in a food that has been preserved properly, according to Estabrook.  To get a clearer picture of the relationship between dietary chemicals and cancer, the committee made several recommendations. Among these were that epidemiological studies should incorporate improved methods to determine human exposure, susceptibility and cellular damage; that concentrations of natural and synthetic chemicals in foods should be better quantified; and that better animal tests, other than the rodent assay, should be developed to screen for carcinogens and non-carcinogens.  Until these research tools are available, the committee concluded, the best way to reduce cancer risk through diet alone would be to make sure that the diet is varied, balanced and nutritious -- just as you've always known.Technology Tames the Food Allergy "Threat"  Of all the dietary dangers consumers face today, food allergies could well be the most misunderstood -- and the most feared. The same people who appreciate the importance of limiting calorie and fat intake seem just as likely to shun foods like dairy products on the grounds that they're "lactose intolerant," or ingredients like MSG, claiming that they're "allergic."  According to the American Academy of Allergy and Immunology, as many as one-third of adult Americans believe they have food allergies. In fact, however, fewer than 2% of the adult population actually do have true food allergies. About 5% of children are diagnosed with food allergies, but these are often outgrown by adulthood.  A true food allergy is an adverse reaction to a food or food component that is otherwise harmless. The reaction can vary in both nature and severity, ranging from mild to life-threatening, but it always involves the immune system. Most often, the allergenic culprit is a protein.  The widely cited condition called "lactose intolerance" is not an allergy, but a genetic condition in which the body lacks the enzyme lactase to digest the milk sugar lactose. Only an estimated 6% of the Caucasian population is truly lactose-intolerant, whereas that percentage is much greater for other groups -- ranging as high as 60% to 70% among Orientals, according to Steve Taylor, Ph.D., chairman of the food science and technology department at the University of Nebraska, Lincoln.  Some people who are lactose-intolerant actually can consume some milk, notes Taylor. By contrast, "if you're allergic to milk protein, you can't tolerate any dairy products," he adds.  Greg Miller, Ph.D., vice president of nutrition research at Dairy Management Inc., says that when strict diagnostic tests are applied, roughly 1% to 3% of infants and children turn out to be truly sensitive to cow's-milk protein. Unfortunately, parents or health professionals may rush to eliminate dairy products from the child's diet based on a reaction that may or may not be related, he says.  In those cases, the child's health may, in fact, be compromised unnecessarily, according to Miller, who notes that dairy products are primary dietary sources of calcium, as well as several other minerals and vitamins. "Often, that's not the right answer -- or the safe answer," he says.  Like lactose intolerance, "MSG symptom complex" is far less common, and far less dangerous, than many consumers believe. Nor is MSG, or monosodium glutamate, a true allergen, says the American College of Allergy, and Immunology.  MSG, the salt of gIutamic acid, has been used for centuries in Asia to enhance the flavor of foods. "Free" glutamate, which is not chemically bonded to amino acids, is present in many foods and performs the same function.  Late last year, a study by the Federation of American Societies for Experimental Biology reported to the U.S. Food and Drug Administration that MSG should be considered safe for most people at levels normally consumed. Although some people are sensitive to MSG, the report said, their reactions are set off only by very high doses. What's more, their symptoms -- including the headaches, nausea and other reactions commonly cited -- are only temporary.  The report identified one group as being more susceptible: asthmatics, who can experience breathing difficulties brought on by large doses of MSG. Both MSG and hydrolyzed vegetable protein, which is high in free glutamate, must be listed on food labels. Still, because of the reaction in asthma patients, FDA is considering additional labeling regulations for foods that contain significant amounts of MSG.  A potential headache for food designers attempting to comply with such a regulation would be created by the wide range of free glutamate from food to food, notes Mark Meskin, Ph.D., R.D., director of nutrition education programs at the University of Southern California School of Medicine, Los Angeles.  Many popular foods, including some produce, are actually quite high in naturally occurring free glutamate, says Meskin. Among those popular favorites that MSG-phobes would have to avoid are two distinctly non-Asian staples: tomatoes and Parmesan cheese.  Another challenge for food designers is that in the case of foods that some people really are allergic to, "the industry has no way to really control the problem," says Taylor. Although labeling regulations are thorough enough so that consumers can identify allergens in a food product, there is still the potential for cross-contamination of shared equipment.  Peanuts, for instance, are among the most common food allergens. Therefore, any ice cream, bakery, cereal or other plant that turns out peanut-flavored products must be a model of state-of-the-art cleaning procedures.  Beyond good housekeeping, effective testing methods would go a long way, toward preventing consumer complaints -- not to mention product recalls. As yet, however, truly effective tests are under development but are not commercially available, according to Taylor.  At the University of Nebraska, ELISA tests (enzyme-linked immunosorbent assays) have been developed for peanut and milk proteins, and there are a few other tests here and there.  With the development of effective testing, inadvertent exposure to food allergens should be greatly minimized. Convincing the public that food allergies are not a threat to the vast majority of consumers is another matter.Back to top<