How Do We Know GMOs Are Safe?

The scientific evidence accumulated over the past decades is clear: genetically modified foods, or GMOs, are safe. In 2013, a team of Italian scientists published a massive review on the subject. They analyzed 1,783 studies on the safety and environmental impact of GMOs, covering the years 2002 to 2012, and did not find a single piece of research showing that GMOs harm human or animal health.

In 2014, another study examined 29 years of GMO use in livestock feed and animal health, comparing the period before and after genetically modified feed was introduced. That amounted to data from 100 billion animals—moving from a time when feed was entirely non-GMO to a point where 90% of it was GMO-based. The result: no difference in animal health.

The most comprehensive review ever conducted on GMO food safety came from the U.S. National Academy of Sciences, Engineering, and Medicine. After examining hundreds of studies, listening to activist testimony, and reviewing hundreds of public comments, the Academy’s conclusion was unequivocal: there is no evidence that GMO foods are any different from non-GMO foods in terms of safety.

The report also compared public health data from the United States, where most crops are genetically modified, with the United Kingdom, where GMOs are almost absent from the market. No differences were found in cancer, autism, allergies, celiac disease, diabetes, or obesity rates.

If GMOs truly caused cancer or any of these conditions, wouldn’t we already be seeing epidemics of cancer, autism, and allergies in the billions of animals fed almost exclusively on GMO feed—or in the U.S. population compared to the U.K.?

Beyond safety, scientific evidence also shows that GMOs are more efficient, require less water and land, and use fewer pesticides. Feeding the planet exclusively through small-scale organic farming is not feasible: it would consume more natural resources at a much higher cost.

Causes of Fear

So why is there still so much fear of GMOs?

When I asked this question among friends, the common answers came up—“we don’t have enough testing,” “we don’t know the long-term effects,” “I heard it causes cancer.” But one reply summed it up perfectly: “I just think the less we mess with things, the better.”

That “less we mess with things” captures our fear of the unknown—and the myth of the “natural” food. Since the Industrial Revolution and rapid urbanization, modern humans have grown so distant from farming that we no longer know how agriculture actually works. We romanticize the idea that humanity could live only on what the land “naturally” gives us, through small family farms—forgetting that there simply aren’t enough families to cultivate the land needed to feed 8 billion people. And in truth, nothing we eat today exists without human intervention, selection, and genetic modification.

Over 10,000 years ago, when humans were hunter-gatherers, we truly lived off what nature provided. Everything we ate was “natural” in the sense of untouched by human influence. But as soon as we began domesticating plants and animals, almost nothing we consumed could be called wild anymore. None of our major crops—rice, corn, soybeans, wheat, cotton—grow freely in nature or could survive without human care.

Old-School Genetic Manipulation

Just as we domesticated animals by selecting traits we liked, we did the same with plants. Think of dog breeds: all of them were created through artificial selection, by taking advantage of spontaneous mutations and breeding animals with desired traits.

The same process unfolded in agriculture. Once humans settled down and began farming, we interfered with nature permanently. Wild wheat, for example, naturally dropped its seeds onto the ground—great for the plant’s reproduction, but useless for the farmer. A mutation that prevented seeds from falling meant farmers could collect and plant them where they wanted. From then on, humans began choosing plants that were tastier, easier to harvest, or more colorful.

Over time, techniques advanced. Farmers discovered hybridization—manually crossing plants to combine traits—which produced larger, hardier crops. Even today, organic farming relies on hybrid seeds purchased every season, because their desirable traits don’t pass on reliably.

Later came mutation breeding: exposing seeds to gamma radiation or chemicals like EMS (ethyl methanesulfonate) to create new variations. Some worked out brilliantly—like orange carrots, selected in honor of the Dutch royal family, which turned out to be rich in beta-carotene. Others were disasters, like a toxic celery variety that caused severe skin reactions in farmworkers, or a potato that fried beautifully but upset consumers’ stomachs. These products made it to market because conventional breeding methods have no regulatory oversight—unlike GMOs.

Enter the GMOs

Genetic engineering changed everything. A GMO is created in the lab by inserting a specific gene—sometimes from another plant, sometimes from bacteria or viruses—into a chosen spot in a plant’s DNA. Gene exchanges happen naturally in evolution all the time; the human genome itself contains genes from ancient viruses and bacteria. The difference is that transgenics allow scientists to do this precisely, knowing exactly which DNA is altered.

Most importantly, GMOs undergo years of strict testing for food safety, human health, and environmental impact—on average, about 10 years before approval. Conventional methods face no such scrutiny. This means if a GMO poses a problem, it doesn’t make it to market.

So why the fear? Perhaps because most people don’t realize that everything we eat has already been genetically modified in some way—and that we’ve been consuming products of genetic engineering for much longer than we think.

Cheese and Insulin

Since 1976, genetically modified bacteria have been producing human insulin—transforming the lives of diabetics, who previously had to rely on insulin from pigs and cows.

Cheese production also relies on GMOs. Until the 1990s, the enzyme rennet, used to curdle milk, was extracted from calf stomachs. Today, thanks to GM bacteria, that same enzyme can be produced cheaply and without killing animals. Many modern vaccines and growth hormones are also developed using GMO technology.

The Scientific Consensus

There is no scientific basis for keeping alive the supposed controversy about GMO safety. The debate is as artificially manufactured as climate change denial or anti-vaccine rhetoric.

After decades of rigorous studies, reviews, and analysis, the scientific consensus is clear: climate change is real, vaccines are safe, and genetically modified foods pose no risk to human health.

✍️ Natalia Pasternak is a researcher at the Institute of Biomedical Sciences at the University of São Paulo (USP), national coordinator of Pint of Science Brazil, and president of the Instituto Questão de Ciência.