Genetically modified (or GM) foods have been with us since the 1990s, and most of us are probably eating them on a regular basis. A genetically modified organism (GMO) is a plant or animal that has had its DNA artificially modified. This is usually done by inserting genes for certain traits that are beneficial to growers or consumers. There are obvious advantages - these genes may increase the plant’s resistance to pests, make the crop more tolerant to existing pesticides or, in some cases, improve the nutritional content, taste or appearance of the produce. Yet campaigners against this technology have raised questions about the safety of consuming genetically modified foods, and about possible dangers to the environment. Let’s take a closer look at these, to see how worried you should be.

Health concerns

Some of the popular health concerns about GMOs are based on scaremongering and poorly understood science (no, your body can’t incorporate genetically modified material into your own DNA), but there are certainly some that are worth considering.

At this point it’s worth remembering that GMOs aren’t a single entity; there are many different GM plants currently being grown, and more in development. And it’s certainly possible to genetically engineer a plant in a way that makes it harmful to human health. What we need to know is whether the current systems of testing, research and regulation in place are sufficient to keep us safe.

Representatives of the industry point out that there are rigorous testing requirements for GM crops before they are approved. They point to cases where crops in development have been axed because they contain particular proteins known to provoke allergies in humans. Critics, on the other hand, focus on the consequences if something slipped through the net - an unknown allergen, for example, or a subtle effect of the insecticidal toxins produced by some GMOs.

Environmental concerns

The other important question is whether GMOs might have unforeseen consequences for the environment. Ecosystems are complex, and the long-term consequences of planting GM foods are hard to predict. There are concerns that GM crops could pass their modified genes on to wild plants, thus changing their role within the ecosystem; or that insect resistant GMOs might harm the bees or butterflies important for pollination. Conversely, proponents of genetic engineering argue that GM crops have, in many cases, been shown to have a lower impact on the surrounding environment and reduce biodiversity to a lesser degree than conventional crops.

So, what does the evidence say?

The biggest systematic review of the evidence to date, published in 2013, concluded that as far as we can tell, there’s probably no cause for concern.

“We have reviewed the scientific literature on GE crop safety for the last 10 years that catches the scientific consensus matured since GE plants became widely cultivated worldwide, and we can conclude that the scientific research conducted so far has not detected any significant hazard directly connected with the use of GM crops.”

That conclusion is subject to a bunch of caveats, which we’ll deal with below.

Concerns about the pesticides used alongside GMOs

Another set of concerns centers not around the genetically modified plants themselves, but on the pesticides used alongside them. One that has attracted much attention is glyphosate - a product sold under the trade name Roundup. Some of the earliest GM crops were developed to be resistant to glyphosate, so that farmers could use the pesticide without killing their crops, obviously making it a more appealing product. Evidence regarding the toxicity of glyphosate in humans is contradictory, but it’s recently been classified by the World Health Organization as “probably carcinogenic” (the same category that bacon was recently moved into). The devil is in the tolerance level, though: many things are bad for you in large enough concentrations. How likely is it that you’ll consume enough to damage your health? And how big is the increased risk we’re talking about? They’re good questions (and as you’ve probably guessed by now, not simple ones) but since this is really about herbicides rather than GMOs per se, that’ll have to wait for another day.

Uncertainty, and the burden of proof

Absence of evidence is not evidence of absence, and failing to find a risk doesn’t necessarily prove that something is safe.

Opponents of GM technology claim that without conclusive evidence for the safety of GMOs, we shouldn’t use them. They argue, reasonably enough, that the burden of proof should lie with the advocates of genetic modification.

This raises another question, though. What level of risk should we regard as acceptable? Our first instinct might be that we only want to use technology that is completely safe - but the reality is that we’re already dealing with and managing risks in our food supply all the time. We take individual risks with our foods every day: food poisoning, allergens, cancer. Some of them are well understood, others hardly at all. Likewise, all agriculture has an effect on the environment in one way or another; and research suggests that in some cases the impact of GM crops may be lower than that of conventional crops.

Do GMOs introduce any novel risks that are substantially different or greater than those we are already managing? Not that we know of.

The strongest argument for caution is that we don’t know how much we don’t know. Some authors have criticized the lack of standardization within the risk assessment process. Possible risks that have been identified can be investigated and studied, but if there are possible risks that we’re not aware of, then we may not be looking in the right place to spot them. We have relatively limited data about the long-term effects, on either human health or the environment. The worry is that if GMOs did turn out to be harmful, then by the time that’s been conclusively demonstrated it might already be too late to reverse the damage.

Conflicts of interest

Much of the research on GMOs has been either conducted or funded by people and companies involved in the biotech industry. Because of the amount of money involved, there’s a relative lack of independent research on the subject. One review checked whether authors affiliated to the industry were more likely to produce papers that were favorable to GMOs, and that case. This is certainly something to be aware of when interpreting the evidence.

Conflicts of interest cut both ways, though. As with many highly polarized topics, GM technology attracts the interest of many people who are either strongly in favor or strongly against. Anti-GMO organizations and lobby groups also produce material supporting their position, and this should be reviewed just as critically.

Verdict

The scientific consensus is that this one is FALSE as far as we know, but we can’t eliminate the possibility that there are hazards that haven’t come to light yet.

Other arguments for or against GM crops

That’s not the end of the discussion. Environmental and health issues aside, there’s still debate and controversy about the wider picture: for example, the advantages or disadvantages of GMOs to developing countries, the social and economic considerations that stem from the existence of the technology, and the business practices of some of the major biotech companies. As with the environmental questions, it is difficult to predict what effect this technology will have on our food supply (and society as a whole) in the longer term; there are no straightforward scientific answers that can help us here.

In a nutshell: GM foods are most likely safe to eat, but there are other potential reasons to be concerned about the technology. How worried should we be? That’s hard to answer. Either way, though, we benefit from taking a careful, considered look at the evidence for and against, rather than jumping hastily to a conclusion.