A small proportion of the population is allergic to one or more food products. Some of the most common allergies are to cow's milk, eggs, soybeans, wheat, peanuts, and various tree nuts. Allergic reactions to foods range from very mild to severe. In the most serious cases, a person exposed to an allergen has difficulty breathing, swelling in the mouth and throat, and decreased blood pressure, conditions that can lead to anaphylactic shock and even death.
A potential problem arises, then, if a gene from a potential allerÂgen-containing plant is transferred into a food plant. For example, in the early 1990s, Pioneer Hi-Bred International, Inc., a DuPont subsidiary, developed a transgenic soybean that contained a gene taken from the Brazil nut (Bertholletia excelsa). The gene transfer was intended to create a soybean containing more of the amino acid methionine, an essential nutrient in which soybeans are normally deficient. It did so, but studies at the University of Nebraska showed that it also conferred the allergenic characteristics of the Brazil nut, making the transgenic soybean itself allergenic. People with food allergies learn early to adjust their diet so as to avoid exposure to allergenic foods. But a person allergic to Brazil nuts might feel safe eating a soybean product, not realizing its allergenic potential. When informed of the results of the Nebraska study, Pioneer disconÂtinued its research on the Brazil nut-enhanced soybean. The case illustrates the potential, however, of the transfer of allergens during genetic transformations.
Perhaps one of the best-known problems associated with the posÂsible appearance of allergens in modified foods involved a product known as StarLink corn, developed by Aventis CropScience in the 1990s. StarLink corn was engineered to include a gene for the syntheÂsis of an insecticidal protein called Cry9C, originally isolated from a strain of the bacterium B. thuringiensis tolworthi. The engineered plant was designed to be resistant to two major pests, the European corn borer and the southwestern corn borer, and possibly also to the black cutworm. StarLink was approved for use in the United States as an animal feed and for industrial applications, but not for human consumption.
In September 2000, DNA fragments from Cry9C were detected in taco shells being sold for human consumption. The amount of the engiÂneered protein was very small, estimated to be less than 0.01 percent by weight, the lowest level of test sensitivity. But Aventis and others were concerned that the protein might cause allergic reactions in people who ate the engineered corn. Within a matter of days, Aventis announced that it would no longer authorize the sale of StarLink corn for the 2001 season, and food stores announced a recall of taco and other corn products that might contain the engineered corn.
At the same time, various regulatory agencies in the United States began a review of possible health risks from exposure to StarLink corn. By mid-2001, three of the most important agencies had issued statements and reports generally favorable to Aventis. On October 12, 2000, the Environmental Protection Agency stated, the "EPA does not have any evidence that food containing StarLink corn will cause any allergic reaction in people, and the agency believes the risks, if any, are extremely low." Two months later, a special Scientific Advisory Panel released an "Assessment of Scientific Information Concerning StarLink Corn" to the EPA that found "a low probability of allergenicity in the exposed population." Finally, in June 2001, the Centers for Disease Control and Prevention (CDC) delivered its study to the FDA, which focused especially on individuals who reÂported that they had developed allergic reactions as result of eating products containing StarLink corn. Although these people had sufÂfered allergic reactions, the CDC panel concluded that StarLink was not the cause: "These findings do not provide any evidence that the reactions that the affected people experienced were associated with hypersensitivity to the Cry9c protein." In spite of this generally faÂvorable response, Aventis withdrew StarLink corn from commercial use in October 2000.
Toxins are a second source of concern about the possible health effects of GM foods. Plants have evolved an amazing array of toxins known as phytotoxins to resist attacks by predators ranging from bacÂteria, fungi, insects, and herbivores to human beings. For example, the potato plant produces glycoalkaloid toxins. The glycoalkaloids are a family of complex organic compounds that contain sugars, alkaloids (heterocyclic compounds containing nitrogen), and other organic groups. The glycoalkaloids cause a number of human health problems; they can depress the central nervous system, cause canÂcer, and inflame the kidneys. Two types of glycoalkaloids commonly found in plants are the solanines and the chaconines, whose strucÂtural formulas are shown on page 119.
Since the glycoalkaloids are destroyed by heating and are toxic in only rather large concentrations, they usually do not endanger human health. However, some critics of genetically altered foods point out that gene transfer might inadvertently deliver a phytotoxin gene into a food plant, putting human health at risk. Thus far there appears to be no example of such an event having occurred.
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a-Chaconine
Chemical structures of a-solanine and a-chaconine
As discussed earlier in this chapter, recombinant DNA techÂniques can be used to confer resistance to certain antibiotics (such as tetracyclin and kanamycin) to a host organism. This step in the recombinant process is a common one because it is an easy way for researchers to find out which organisms in a study have actually incorporated the gene to be transferred. But the practice could conÂceivably threaten human health. For example, suppose that a food engineered to contain a gene conferring some desirable characterÂistic (such as an increased level of some nutrient) also contained a gene for antibiotic resistance. If a person ate the GM food and later found it necessary to take the corresponding antibiotic to treat an illness, what would happen? One might expect that the antibiotic would be destroyed by the gene, and that the person would receive no benefit from the medication. Again, no studies exist confirmÂing that such effects have actually occurred as a result of eating GM foods. Given how difficult it would be to detect such effects, however, it is not entirely surprising that some people worry that unwanted antibiotic resistance will spread to the human populaÂtion in this manner.
As is apparent from the preceding discussion, a fair number of concerns about the possible effects of GM food on human health have been expressed both by scientists and nonscientists. Although one cannot dismiss the possibility that these effects, or others not yet imagined, could happen, scientific support for such concerns is relatively thin. A report by Jose L. Domingo, of the faculty of Medicine and Health Sciences at Spain's Rovira i Virgili University, underscores this point. Domingo undertook an extensive survey of scientific research on the adverse effects of GM foods that had been conducted as of 2000. Of the 212 reports he reviewed, only seven cited the results of scientific studies on this question. The remaining articles, he discovered, contained comments, opinions, viewpoints, and other observations about GM food without any supporting sciÂentific evidence.
Introduction
The History Of Food Modification
Food Additives
Synthetic Foods
