What Are Genetically Modified Organisms (GMOs)? A Detailed Scientific Guide

You may have noticed a new phrase on the packaging of your favorite breakfast flakes or crispy snacks: “Contains a bioengineered food ingredient." That’s because since January 2022, the U.S. Department of Agriculture (USDA) has required this language to be displayed on the packaging of some products that contain substances called “genetically engineered ingredients,” “genetically modified organisms,” or, as they're more commonly known, “GMOs.”

A GMO is a food or crop with genetic material that has been altered using biotechnology instead of selective breeding.

Although GMO may feel like a new term, manipulating the genetic makeup of the food we eat is anything but.

“Everything we buy in a supermarket has been genetically modified," says Diane Beckles, PhD, a plant sciences professor and researcher at the University of California in Davis. Through selective breeding, “Humans have been changing the genetic makeup of plants for thousands of years.” As the National Academies of Sciences, Engineering, and Medicine explains, selective breeding involves mating plants with desirable traits so that future generations of the plant will have those traits.

Now biotechnology allows scientists to make direct changes to a plant’s genes to produce desired characteristics. “What we have the ability to do now is to make those changes very precisely. We have the knowledge to go in and edit, tinker, add DNA and remove DNA in specific parts of the genome of plants,” Dr. Beckles says.

Genetically engineered crops were introduced in the United States in 1996, according to the USDA. The major GMO crops in the United States include herbicide-tolerant and insect-resistant corn, cotton, and soybeans; but according to the USDA, herbicide-tolerant crops are also used in the production of alfalfa, canola, and sugar beets. Other genetically engineered characteristics have been developed, including resistance to viruses, fungi and drought, as well as enhanced protein, oil, or vitamin content.

“I don’t think many consumers are aware [of GMOs],” says Lauri Wright, PhD, RDN, a clinical registered dietitian-nutritionist, the director of the center for nutrition and food security at the University of North Florida in Jacksonville, and president-elect of the Academy of Nutrition and Dietetics. Indeed, only about one-quarter of American adults always or sometimes check to see if products have GMO ingredients when they are shopping, according to a 2015 survey by the Pew Research Center.

“This label will help consumers make choices based on their preferences,” Dr. Wright says.

The reality is GMO ingredients are widespread in the food we eat, Beckles says. More than 90 percent of corn and soybeans planted in the United States, for instance, are genetically engineered.

The U.S. Food and Drug Administration (FDA) describes two basic types of crop genetic modification:

• Genetic engineering A gene with a desirable trait is copied from one organism and inserted into the genome of another in what is known as a transgenic process. An example is insect-resistant corn, which was created using a gene within the soil bacterium Bacillus thuringenesis.
• Genome editing Genes are added, removed, or altered within an organism’s genome without the introduction of foreign genetic material. An example is the Sicilian rouge tomato that is sold in Japan, which through the CRISPR process of genetic editing contains a high amount of the nutrient gamma-aminobutyric acid (GABA), as research in the December 2021 Nature Biotechnology noted.

Beckles describes another technique for developing GMOs that comes under the second category, called RNA interference (RNAi). As the National Library of Medicine notes, in this process a cell is manipulated into destroying a segment of its own RNA and the protein it encodes, thereby reducing the gene’s expression of a particular trait. Scientists created the Arctic Apple, which does not brown when cut, using this technology.

There are additional techniques for bioengineering food, but they are less commonly used.

Several GMO crops are grown and sold in the United States for human and animal consumption, according to the U.S. Food and Drug Administration (FDA), including:

• Corn
• Soybeans
• Sugar beets
• Potatoes
• Summer squash
• Apples
• Canola
• Cotton (for both textiles and oil)
• Alfalfa

Other foods that come in bioengineered forms around the world include eggplant, papaya and salmon, the USDA reports.

“Absolutely,” says Wright. “Genetically modified foods have been well studied.” She points out that the USDA has approved the GMOs on the market as being safe for human consumption. Plus, a study by the National Academies of Sciences, Engineering, and Medicine found no evidence that genetically engineered plant crops that were commercially available carried any more risk to human health than conventionally bred crops.

More recently, the National Academies has stated that foods with GMO ingredients aren’t harmful and don’t pose a higher health risk than non-GMO food. When scientists compare health trends in North America to trends in Europe, where genetically engineered crops are rare due to widespread opposition, they have not found differences in “patterns of cancer, obesity, diabetes, kidney disease, gastrointestinal problems, celiac disease, autism, or food allergies,” say the National Academies.

Furthermore, there are advantages to using GMOs, says Wright, from increasing food production using herbicide-tolerant and insect-resistant crops, to enhancing the nutritional value of food as a bulwark against malnutrition. She points to so-called golden rice, which is genetically modified to produce beta-carotene, which is converted into vitamin A by the body. It gets its golden hue from the nutrient and is designed to help address widespread vitamin A deficiencies in developing countries. You won’t find it available yet in the United States or most other countries, but farmers in the Philippines have begun harvesting the grain, according to Time.

Another example is the aforementioned Arctic Apple, which is sold in the United States in bags of precut slices. Methods commonly used to control apple slice browning include sulfites, which can cause allergic reactions. "You prefer not to have these apples dipped in chemicals,” says Beckles. RNAi technology has been used in the Arctic Apple to block an enzyme that causes browning when apple flesh is exposed to oxygen in the air, as research details.

Over the years, GMO crops and ingredients have been a source of controversy, despite widespread scientific agreement about their safety. Among respondents to the aforementioned Pew survey, 37 percent reported believing that genetically modified food is safe, compared with 88 percent of scientists in the world’s largest multidisciplinary scientific professional society, who say such foods are “generally safe.” Yet two-thirds of the public believe that scientists don’t have a clear understanding about the health effects of GMOs.

Historically, negative public sentiment about GMOs have contributed to banning and restrictions in nations around the world. For instance, 19 European Union (EU) member states have opted out of genetically modified crop cultivation in all or part of territories, according to the USDA; still, a number of countries in the EU do import genetically modified soybean, corn, and rapeseed products, mainly for feeding livestock and poultry.

Reasons for being opposed to GMOs include:

• Concerns about food safety
• Dependence on corporations who may grow food in ways that may be cost-prohibitive for small farmers
• Environmental impacts of changes in food cultivation practices caused by using herbicide-resistant crops

Beckles chalks up the differences between the European and American regulatory approaches to politics and differing attitudes toward corporations. “America is more capitalist. Here, I would think that corporations have more power with the U.S. government than what we would see in Europe, and the European politicians have basically ignored science. They’re letting their populations drive a fear-based approach to GMOs.”

Europeans aren’t the only ones approaching GMOs with caution. Despite assertions by the inventors of golden rice that the GMO can address malnutrition and save lives, it has only been cleared for cultivation in one country, per the International Rice Research Institute. Opponents say there are cheaper solutions to addressing vitamin A deficiency that don’t require dependence on GMOs and the biotechnology companies that could ultimately profit from their widespread cultivation.

Despite all that, international opposition appears to be softening against the latest generation of GMOs: gene-edited organisms. In July 2023, the European Commission proposed loosening restrictions on gene-edited plants after a review of its regulations.

So-called new genomic technique (NGT) plants that could also occur naturally or be obtained through conventional breeding techniques would be treated like conventional plants and exempted from GMO legislation. They would not have to be labeled any differently from conventional plants. Other NGTs, such as those that involve species that are not sexually compatible in nature, would still be subject to GMO rules.

Beckles explains why such distinctions are being made. Unlike the earliest-introduced GMOs, which use foreign material such as bacteria to modify a plant’s genome, gene editing does not involve the introduction of foreign material or large changes to the DNA of the organism. She gives the example of wheat and the four basic building blocks of DNA named adenine (A), cytosine (C), guanine (G) and thymine (T), billions of which shuffle and combine in complex strands to determine its characteristics.

“Wheat has 16 billion of those letters, and with gene editing you can change one letter. And if you do it in the right gene and in the right part of the gene, you can get a beneficial change — maybe a wheat that uses nitrogen differently, that needs less fertilizer or that makes high-fiber starch or that flowers earlier. That's why gene editing is so powerful. It relies on our knowledge of what the genes are doing in the plant, but we can do it with such precision and accuracy that we hardly make any changes at all,” she says.

You may wonder if the U.S. scientific community’s assurances about GMOs and human health extend to animals. The National Academies state that scientists agree, based on available data, that eating GMO crops does not affect the health of animals, according to the National Academies.

Widespread adoption of herbicide-tolerant crops has brought diminishing returns over time. Roundup Ready crops are genetically engineered to resist the effects of glyphosate, which is the herbicide in the Roundup weed killer manufactured by Monsanto. These crops have allowed for increasingly widespread use of Roundup in American agriculture, according to Harvard University's Science in the News. “We were using so much herbicide, it was just a matter of time before weeds would develop resistance to it,” says Beckles.

In the short term, farmers may use even more Roundup to keep pace with the weeds, she points out. That raises concerns about the environmental effects of this practice. The Environmental Protection Agency says that glyphosate is safe for human health when used as directed, and that its residue on foods does not pose a health risk as long as it is kept to legal residue limits. But there are spraying restrictions to address a “potential risk to terrestrial and aquatic plants and birds, and low toxicity to honeybees,” per the U.S. Environmental Protection Agency.

The problem may soon become moot, however. “At some point, it's no longer effective, so farmers are having to look for glyphosate alternatives.” Of the Roundup Ready crops themselves, Beckles says, “While there are no harmful effects on human health, I do think that [critics] are rightfully concerned about the ecological effect of growing those crops.”

A simple way to determine if your food has GMOs is to look at the bottom of the nutrition label on the package.

According to the USDA, other indicators to look for include:

• A round symbol on the package that says “bioengineered”
• A QR code that links to online information about the product’s ingredients
• A phone number that you can text for more information about the product’s ingredients

You might also see the words “derived from bioengineering” or “ingredients derived from a bioengineered source” on a nutrition label. The agency says those products don’t contain detectable amounts of bioengineered material and that such disclosures can be voluntary.

Keep in mind the new food labeling law doesn’t cover all foods that contain GMOs. As the Congressional Research Service points out, GMOs developed by gene editing may not fall under the labeling regulations if their modifications could be achieved by selective breeding or found in nature. In a 2020 report the CRS listed the following materials as not requiring disclosure:

• Animal feed (because it is not food intended for human consumption)
• Foods in which modified DNA is not detectable, such as refined oils and sugars
• Incidental additives

What’s more, food served in restaurants doesn't require disclosure.

Critics of GMOs, such as the Non GMO Project, are calling for transparency in labeling standards. “With so much remaining outside the scope of the BE labeling law, looking for a ‘bioengineered food’ label may not be effective at keeping GMOs out of your shopping cart. These undisclosed genetically modified ingredients still contribute to GMO agriculture and acreage and the destructive, chemical-dependent practices that go with it,” the organization says in a blog post.

Beckles suggests taking the steps you need to feel secure about the crops that go into the food you eat. “I understand that it’s strange to think of humans having precise control over how plants are made and that it’s very disconcerting. And it is always possible to insert genes that may be harmful. But the crops that are on the market are essentially safe.”