From breakfast cereal to beef jerky, more than 70 percent of processed food in the U.S. is made with genetically modified organisms (GMOs). Farmers have enhanced their crops for centuries through a process called selective breeding, in which they breed plants for specifically desirable traits. It's how we got sweet corn and seedless watermelon. Genetic modification, however, takes things one step further by adding genes from other organisms into a crop.

So, why change the food nature gave us? Most genetic modification today helps farmers increase the amount of food they grow through two seemingly contradictory ways. On the one hand, genetically modified food can be resistant to certain pests (like insects or weeds). Say a beetle is killing all of your tomato plants. You can add a gene to the plant that acts as a beetle repellant and stops you from needing to spray your crops with pesticide. On the other hand, crops can be modified to be resistant to weed killers, which means you can spray entire fields with herbicide, easily knocking out every stray weed in sight without any risk of damaging the big moneymakers.The impact of altered herbicide residues in transgenic herbicide-resistant crops on standard setting for herbicide residues. Kleter GA, Unsworth JB, Harris CA. Pest management science, 2011, Aug.;67(10):1526-4998.

Aside from making crops stronger, modification can make the food more nutritious by adding vitamins, minerals, and proteins, or it can improve taste by making the food juicier with more intense flavor and color.Metabolic engineering of the omega-3 long chain polyunsaturated fatty acid biosynthetic pathway into transgenic plants. Ruiz-López N, Sayanova O, Napier JA. Journal of experimental botany, 2012, Jan.;63(7):1460-2431. Genetic engineering for increasing fungal and bacterial disease resistance in crop plants. Wally O, Punja ZK. GM crops, 2012, Jan.;1(4):1938-2006.

Fiddling With Food

Are GMOs safe? Sure, this all sounds great for farmers, but what about us, the people eating the food? The process of spraying fields willy-nilly with weed killer is particularly concerning to GMO activists because these herbicides then end up in our food supply. And studies suggest ingesting such compounds can be associated with gastrointestinal, neurological, and cardiovascular problems, especially in the elderly and others with weak immune systems.Acute human glufosinate-containing herbicide poisoning. Mao YC, Hung DZ, Wu ML. Clinical toxicology (Philadelphia, Pa.), 2012, Apr.;50(5):1556-9519. Plus, studies on both rats and fish have shown that ingesting weed killer can cause cell and tissue damage in the kidneys, liver, heart, and adrenal glands.Roundup causes oxidative stress in liver and inhibits acetylcholinesterase in muscle and brain of the fish Prochilodus lineatus. Modesto KA, Martinez CB. Chemosphere, 2009, Nov.;78(3):1879-1298.
Roundup effects on oxidative stress parameters and recovery pattern of Rhamdia quelen. de Menezes CC, da Fonseca MB, Loro VL. Archives of environmental contamination and toxicology, 2010, Aug.;60(4):1432-0703.

Some scientists also worry that transplanting genes from one organism to another may cause deadly allergic reactions. So peanut allergy sufferers beware: One ongoing study is experimenting with using a protein from peanuts to extend the shelf life of vegetables. Another study on soybeans enhanced with a protein from Brazil nuts found that the allergen from the nut transferred to the soybeans.Identification of a Brazil-nut allergen in transgenic soybeans. Nordlee JA, Taylor SL, Townsend JA. The New England journal of medicine, 1996, Apr.;334(11):0028-4793. But before you whip out your EpiPen, the World Health Organization notes there haven't been any cases of allergic reactions from genetically modified food on the market right now.

The Bottom Line

The good news is that all genetically modified food is examined and studied by the United States Department of Agriculture, Environmental Protection Agency, and the Food and Drug Administration for toxicity and allergens before making its way onto grocery store shelves. And despite the fact that some studies have pointed to potentially negative effects, these three agencies, plus a number of additional studies, have determined that GMOs are safe to eat. The drawback: These crops are relatively new—emerging in the mid-1990s—so we'll have to wait to learn if there are any concerning long-term impacts.

Originally published April 2012. Updated September 2015.

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