CHICAGO, ILLINOIS, U.S. — More than half of U.S. consumers say they are concerned about bioengineered ingredients or genetically modified organisms (GMOs), but many are unable to define them, according to The NPD Group. The research firm asked shoppers to describe GMOs in their own words, and the answers varied from “genetically altered” to “not natural,” with many respondents indicating “don’t know.”

The U.S. Department of Agriculture defines genetic modification as “the production of heritable improvements in plants or animals for specific uses, via either genetic engineering or other more traditional methods.”

Consumer awareness of GMOs has heightened in the wake of recent media coverage and several states’ legislative efforts to label them in food products, prompting increased concern among Americans, NPD said. Fifty-seven percent of U.S. adults expressed concern over genetically modified foods in 2014, which compared with 43% of consumers in 2002, according to NPD’s Food Safety Monitor, which tracks consumer awareness of food safety issues and eating intentions. The level of concern has grown over time, with 20% of adults who were “very” or “extremely” concerned about GMOs as of last year, up from less than 10% in 2002.

Despite the surrounding controversy, 44% of shoppers suggested bioengineered ingredients may offer benefits. Potential advantages of GMOs, according to the Center for Food Integrity, include fighting citrus greening disease in Florida, reducing the amount of acrylamide in fried potato products and providing non-browning attributes to apples, which would help prevent food waste.

Still, more consumers are wary, and recent moves from major food companies to eliminate GMOs from products may compound the concern. Chipotle Mexican Grill recently announced it had become the first national restaurant chain to remove bioengineered ingredients from all of its menu items by swapping sunflower and rice bran oil for soybean oil and sourcing non-GMO corn for its tortillas.

Steve Ells, founder, chairman and co-chief executive officer of Chipotle, said, “There is a lot of debate about genetically modified foods. Though many countries have already restricted or banned the use of GMO crops, it’s clear that a lot of research is still needed before we can truly understand all of the implications of widespread GMO cultivation and consumption. While that debate continues, we decided to move to non-GMO ingredients.”