A GMO, or genetically modified organism, is a plant, animal, or microorganism whose DNA has been deliberately changed using genetic engineering. Unlike traditional breeding, which crosses whole organisms and hopes for desired traits, genetic engineering allows scientists to make specific, targeted changes to an organism’s DNA, including inserting genes from a completely different species. The result is an organism with traits that would be difficult or impossible to achieve through conventional methods.
How Genetic Engineering Works
The most common method for creating GMO plants borrows from nature. A soil bacterium called Agrobacterium naturally transfers bits of its own DNA into plant cells. Scientists figured out how to hijack this process in the early 1980s, swapping in genes they wanted the plant to carry. The bacterium does what it’s always done: it delivers DNA into the plant cell, where it becomes part of the plant’s own genome. The plant then passes that new gene to its offspring like any other trait.
A second method, called particle bombardment, physically shoots microscopic gold or tungsten particles coated with DNA into plant cells. It’s less elegant but effective, especially for crops that don’t respond well to the bacterial approach. Both methods achieve the same end result: a plant carrying a new gene that produces a useful protein, whether that’s one that resists insects, tolerates a herbicide, or produces a nutrient it normally wouldn’t.
GMO Crops You Encounter Most Often
The USDA maintains an official list of bioengineered foods available in the United States. It includes corn, soybeans, canola, cotton, sugar beets, potatoes, alfalfa, squash, papaya, apples, pineapple, eggplant, sugarcane, and one animal: salmon. Corn and soybeans dominate. In the U.S., over 90% of corn and soybeans grown are genetically modified, which means GMO-derived ingredients show up in a huge range of processed foods, from corn syrup to soybean oil.
Most of these crops carry one of two traits. Insect-resistant varieties produce a protein from a naturally occurring soil bacterium that’s toxic to specific pests but harmless to humans. Herbicide-tolerant varieties survive applications of weed killer that would otherwise destroy them, allowing farmers to control weeds without damaging the crop. Some newer varieties stack both traits together.
GMOs Beyond the Farm
Food crops get most of the attention, but the first major commercial success of genetic engineering was actually a medicine. In 1982, the FDA approved Humulin, human insulin produced by genetically modified bacteria. Before that, people with diabetes relied on insulin extracted from cow and pig pancreases, which worked but sometimes caused allergic reactions. Scientists chemically synthesized the genes for human insulin’s two protein chains, inserted them into E. coli bacteria, and grew those bacteria in large fermentation tanks. The bacteria produced human insulin that was then purified and packaged for patients. It was the first therapeutic product made with recombinant DNA technology, and it’s still the foundation of how insulin is manufactured today.
GMO microorganisms now produce a wide range of pharmaceuticals, enzymes used in food processing (like the rennet in most cheese), and industrial chemicals. The technology’s footprint extends well beyond the grocery aisle.
The First GMO Food
The first genetically modified food to reach consumers was the Flavr Savr tomato, approved by the FDA in 1994 and marketed by Calgene, Inc. out of Davis, California. It was engineered to ripen without softening as quickly, giving it a longer shelf life. The FDA evaluated it and deemed it as safe as conventionally bred tomatoes. The Flavr Savr was a commercial failure for reasons unrelated to safety (it was expensive and didn’t taste great), but it set the regulatory precedent for every GMO food that followed.
How GMOs Affect Pesticide Use
One of the clearest measurable effects of GMO adoption is reduced insecticide spraying. Insect-resistant corn doesn’t just protect itself; it suppresses pest populations across entire regions. A study published in the Proceedings of the National Academy of Sciences tracked this effect over 25 years. In New Jersey, insecticide use on sweet corn dropped 79% between 1992 and 2016, falling from 2.64 kg per hectare to 0.55 kg per hectare. Pepper crops saw an even sharper 85% decline. Notably, these reductions occurred in non-GMO vegetable crops growing near GMO cornfields, because the pest populations in the whole area had shrunk.
The picture with herbicide-tolerant crops is more complicated. While they simplified weed management initially, some weed species have developed resistance to the herbicides used with these crops, prompting farmers to apply additional or different chemicals. The environmental ledger depends on which trait you’re looking at.
Nutritional Engineering: Golden Rice
Golden Rice is the most prominent example of a GMO designed not for farmers but for public health. Engineers inserted two enzymes into rice that create a pathway for producing beta-carotene, the orange pigment your body converts into vitamin A. Regular white rice contains none. Golden Rice contains up to 35 micrograms of beta-carotene per gram of uncooked rice.
The numbers matter because vitamin A deficiency affects roughly 250 million schoolchildren worldwide and can cause blindness and weakened immunity. A single 100-gram serving of uncooked Golden Rice provides an estimated 500 to 800 micrograms of retinol (the active form of vitamin A), covering 80 to 100% of an adult’s daily requirement. For a child eating about 50 grams of rice per meal, that’s still over 90% of their daily need. It represents a food-based strategy for regions where supplements and dietary diversity remain out of reach.
What the Safety Evidence Shows
The National Academies of Sciences, Engineering, and Medicine reviewed the full body of evidence and concluded that no validated evidence exists showing foods made from GMOs are less healthy than non-GMO foods. Their analysis compared health trends in North America, where GMO-derived foods have been widely consumed since the mid-1990s, with trends in Europe, where such foods are rare. They found no differences in rates of cancer, obesity, diabetes, kidney disease, gastrointestinal problems, celiac disease, autism, or food allergies between the two populations. Animal feeding studies spanning multiple generations have reached the same conclusion.
This doesn’t mean every possible GMO is automatically safe. Each new product undergoes its own evaluation. But the technology itself, and the GMO foods currently on the market, have not produced detectable health harms over three decades of consumption by billions of people.
U.S. Labeling Requirements
The National Bioengineered Food Disclosure Standard requires food manufacturers, importers, and certain retailers to disclose when a food is bioengineered. Mandatory compliance began on June 23, 2025. Companies can meet the requirement through on-package text, a standardized symbol, a QR code or digital link, or a text message option. Small manufacturers have additional flexibility, including phone numbers or web addresses. The standard uses the term “bioengineered” rather than “GMO” on labels, so that’s the word to look for when shopping.
How U.S. Regulation Is Structured
Three federal agencies share oversight of GMOs, each covering a different angle. The USDA evaluates whether a new GMO crop could pose risks to agricultural plant and animal health. The EPA regulates any pesticidal traits built into the plant, such as the insect-killing proteins in Bt corn, and sets limits on pesticide residues in food. The FDA oversees the safety of the food itself, evaluating whether it’s as safe and nutritious as its conventional counterpart. This three-agency system has been in place since the 1986 Coordinated Framework for the Regulation of Biotechnology.
Gene Editing and What’s Changing
Newer techniques like CRISPR allow scientists to make precise edits to an organism’s existing DNA without necessarily inserting genes from another species. You might snip out a gene that causes browning in mushrooms or tweak a gene to boost a plant’s drought tolerance. The result can be identical to what might occur through natural mutation or conventional breeding, just achieved faster and more precisely.
The FDA treats these gene-edited foods the same way it treats all foods: based on the characteristics of the food itself, not the method used to produce it. For gene-edited plants that don’t raise obvious safety questions (because their changes resemble what traditional breeding could produce), the FDA recommends a voluntary meeting rather than the more extensive consultation process that older GMO crops have customarily gone through. This distinction is reshaping how new crop varieties reach the market, potentially bringing a wider range of improved foods to consumers more quickly.