The inserted genes are typically chosen for properties that make them more herbicide-, virus-, disease- or insect-resistant, or that add vitamins and minerals, or that allow them to be more tolerant of extreme weather. Scientists also inject growth hormones in plants and animals to speed their maturity.
Why GM Foods are Controversial
Supporters of GM crops and farm animals list benefits such as plants' faster maturation, increased nutrients, yields and stress tolerance, and better resistance to disease, pests and herbicides. As benefits to raising farm animals they include higher yields of meat, eggs and milk.
But groups like the Institute for Responsible Technology and as large and powerful as the European Union (EU) express concern about both demonstrated and unknown health risks to humans who eat GM foods. Many European countries ban GM foods.
Milk from cows treated with rBGH contains significantly higher levels of a hormone called insulin-like growth factor-1 (IGF-1). Elevated IGF-1 levels have been linked to breast, prostate and other cancers in humans. (In response to consumer concern about rBGH, store brand milk sold by retail giants Safeway, Kroger, WalMart and many others now comes only from cows that have not been treated with rBGH.)
Although there's evidence that genes inserted in GM foods can cause toxic and allergic reactions, still, according to the Institute for Responsible Technology, genetically modified organisms (GMOs) are present in most foods processed in the U.S. The U.S. Federal Drug Administration (FDA) does not require GMO labeling, and Americans who might be opposed to eating GM foods can't tell that they're buying them.
What to do if You're Concerned
If you're concerned that GM foods may be harmful to your health, learn how to avoid them with the help of the non-GMO shopping guide. Tips include eating only organic foods and 100 percent grass-fed animals and wild fish (farmed fish may be raised on GM feed).