Many plants routinely used for food contain toxins (e.g., beans contain lectins, potatoes contain alkaloids). Any method of crop improvement (by traditional breeding practices or through biotechnology), can possibly introduce unknown changes in food composition. New varieties that contain an increased amount of toxic compounds may be hazardous. This is one reason why countries with crop variety registration procedures usually look at certain aspects of food safety before registration of new, conventionally derived varieties.
The first step in a food-safety review is testing of the new protein expressed from the inserted gene. If the protein is not already present in other foods with a proven history of safety to humans, it is thoroughly tested to ensure its safety. Even if the newly expressed protein is well known, studies are conducted with the GM material to confirm its safety and to assess whether any unexpected effects occur in the plant.
Genetic engineering need not make a food inherently different from its conventional counterpart. The technology itself is unlikely to increase the food's probability of containing an allergen. Concern about food allergies, however, is frequently cited as a major consumer issue with GM foods. Fortunately, much is known about foods that trigger allergic reactions—for example, 90% of all food allergies in the United States are caused by a very small number of foods: cow's milk, eggs, fish and shellfish, tree nuts, wheat, peanuts, and legumes.
The amino acid sequence of the new protein is compared to that of known allergens. A very high dose of the expressed protein is fed to laboratory animals to assess toxicity, and immunological tests are conducted to ensure that the newly expressed protein is not an allergen. Digestibility studies are carried out with the purified protein and with the whole food. These tests determine whether the new protein is rapidly digested like other dietary proteins (a trait generally indicating nonallergenicity). If digestion breakdown products result, they are identified and checked for safety.
(Initially there was some concern that virus proteins expressed in virus-resistant GM crops might trigger allergic reactions if included in food. This concern has largely been abandoned since many foods are infected with one or more plant viruses, and viral proteins have been consumed thousands of years without deleterious effects.)
Even genes from sources not known to be allergenic are subjected to detailed allergenicity screens. The level of the new protein in the GM plant and the amount present in parts consumed as food are assessed to estimate how much would be consumed in a normal diet. Studies on whole foods indicate whether the inserted genes or new protein might have an unexpected effect on the normal composition and qualities of the food. Tests are performed to determine whether nutrients, vitamins, and minerals in the new plant occur at the same level as in the conventionally bred plant. Other studies examine whether antinutrients (substances that interfere with nutrient absorption), natural toxicants, or known allergens occur at levels comparable to those in the conventional plant. In some cases, baseline data on conventional foods against which comparisons with GM foods can be made are lacking.
When foods derived from transgenic crops and their conventional counterparts are demonstrated to be essentially the same, the GM food is said to be "as safe as" or "substantially equivalent to" the conventional product. Any significant change in nutrition, composition, or intended use prevents the claim of substantial equivalence. While the first generation of transgenic crops largely fulfils the substantial equivalence requirements, subsequent generations will include many types of food GMOs specifically designed to be nutritionally enhanced and therefore different. For these, substantial equivalence will not be an appropriate measure of safety.
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