Q. What are genetically modified foods, why are they so controversial, and how do I know whether I'm buying them when I go to the grocery store?

A. Genetically modified foods, also called genetically modified organisms, are foods containing genetic material that has been transferred from one organism to another. They are produced to give foods genetic traits that they don't naturally have.

For centuries, farmers have been crossbreeding plants to create hybrids with specific qualities. Producing genetically modified foods, however, is typically carried out by large-scale private biotechnology companies and requires substantially different techniques: genes from animals have been inserted into plants, genes from human beings have been inserted into pigs, and genes from viruses, bacteria and insects have been inserted into fruits, vegetables, and grains.

Proponents argue that genetically modified crops are better able to withstand drought or pests, and may reduce the need for pesticides and herbicides. Some say genetically modified foods may contain increased levels of certain antioxidants, amino acids and other nutrients.

Critics point out that they have not been adequately tested — or not tested at all — for safety. Genetically modified foods contain material that has never been consumed by humans, and may pose allergy threats. For example, some genetically modified tomatoes contain prohevein, an allergen found in rubber latex, because it kills fungus. People who are latex-sensitive may experience allergic reactions when they eat them. In addition, there are serious concerns in the medical community that some genetically modified foods contain antibiotic sequences that may lead to antibiotic resistance in humans.

The environmental impact of genetically modified organisms is unknown, and there is much uncertainty about the unleashing of foreign, untested genetic material into the ecosystem. This is of special concern for the delicate environment of Hawai'i, since more genetically modified crops are reportedly grown here than anywhere else. According to Earthjustice attorney Paul Achitoff, Hawai'i has been called "the genetically modified organism testing capital of the world."

There is no way to know if you are purchasing genetically modified foods at a U.S. grocery store. The European Union requires labeling of all genetically modified foods, and many other countries either require labeling or ban specific genetically modified crops. However, the FDA does not require that genetically modified foods be labeled, so the only way to avoid eating them in this country is to buy 100 percent organic food.

To learn more about the issue in Hawai'i, watch the video "Islands at Risk: Genetic Engineering in Hawaii" on YouTube.com. (Put in the search field "Islands at Risk.") A film on genetically modified organisms in the United States and abroad is available at www.thefutureoffood.com.

Laurie Steelsmith is a naturopathic physician and licensed acupuncturist in Honolulu, as well as author of "Natural Choices for Women's Health" (Random House). Reach her and read columns at www.drsteelsmith.com. This column is for information only. Consult your health provider for medical advice.