For example, scientists found that a soybean containing a gene from a Brazil nut can produce allergic reactions in the blood serum of individuals with nut allergies. Allergic reactions to nuts can be serious and even fatal. Researchers were able to identify the danger in this particular case because nut allergies are common and can be readily tested. In other cases, testing for allergenic potential can be much more difficult. With genetic engineering, familiar foods can start producing substances previously not present in the human food supply, so it is impossible to know who may have allergic reactions.
Genetic engineering can make ordinary, familiar foods become toxic.
In some cases, new characteristics introduced intentionally may create toxicity. As it appears in bacteria, the Bt toxin is considered relatively safe for humans. Bt sprays used by organic farmers, for example, break down quickly after application. When Bt toxin is incorporated into common foods such as corn, we are exposed every time we eat these engineered foods. And of course, a pesticide engineered into every cell of a food source cannot simply be washed off before a meal.