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Scientists Say GMO Foods Are Safe, Public Skepticism Remains

Genetically-engineered crops are as safe to eat as their non-GE counterparts, they have no adverse environmental impacts, and they have reduced the use of pesticides. That’s according to a comprehensive report released by the National Academy of Sciences today—a group founded by the U.S. Congress to provide expert scientifically-based advice on a wide variety of issues.

But the academy also found that GE or (genetically-modified organisms or GMO) crops didn’t increase those crops’ potential yields, and they did lead to widespread and expensive problems with herbicide-resistant weeds.

The report acknowledges that beyond safety, other issues need to be addressed, including earning the public’s trust. It recommends a more transparent and inclusive conversation about GE crops going forward.

The report, two years in the making, is a 388-page, comprehensive look at every aspect of genetically engineered crops. “Sweeping statements about GE crops are problematic because issues related to them are multidimensional,” the report says right up front, and goes on to dig deep on those dimensions.

170.3 million hectares have been planted with genetically-engineered crops, as shown on this map. Courtesy National Academy of Sciences

The assessment is generally positive, but there are many caveats and notes of caution. For those of you who want just the big takeaways, here’s the nutshell version:

  • GE crops are safe to eat.  There is always uncertainty about safety, of course, but there’s no evidence of harm.
  • The GE crops in our food system don’t improve on the crops’ potential yields. They have, however, helped farmer protect yields from insects and weeds.
  • Both herbicide-tolerant crops and crops with the organic pesticide Bt built in have decreased pesticide use, although those decreases came early on, and some have not been sustained.
  • Increased use of glyphosate, the herbicide GE crops tolerate, has been responsible for a widespread and expensive problem of glyphosate-resistant weeds.
  • The report found no adverse affects on biodiversity or danger from interbreeding between GE crops and wild relatives.
  • Although both the use of GE crops and the employment of farming techniques that reduce tilling have been on the rise, the report finds no cause-and-effect relationship.
  • The economic benefits to farmers have been well-documented, although individual results vary.
  • Small-scale farmers may have trouble seeing those economic gains because of the price of seed and lack of access to credit.
  • Appropriate regulation is imperative, and that regulation should be based on the characteristics of the crop, rather than the technique used to develop it, whether GE or non-GE.
  • Ongoing public conversations about GE crops and related issues should be characterized by transparency and public participation.

The report also notes that both genetic engineering and conventional breeding are important to crop improvement. Each method has strengths and weaknesses, and treating them “as competing approaches is a false dichotomy; more progress in crop improvement can be brought about by using both … than by using either alone.”

For those of you who interested in chapter and verse of the report, here is soup-to-nuts rundown of the committee’s findings:

Human Health

The committee doesn’t find evidence the consumption of the GE foods currently in our food supply increase food allergies, have significant effects on the GI tract, or pose a risk for horizontal gene transfer.

It also doesn’t find spikes in health problems like autism, obesity, cancer, and kidney disease that correlate to the introduction of GE foods.

The committee acknowledges small differences in gut microbes in some animal experiments, but conclude that GE foods “are not expected to cause health problems.”

On allergenicity, the committee recognizes that “[t]here are limits to what can be known about the health effects of any food, whether it is produced through conventional breeding alone or in conjunction with genetic engineering.”

All in all, the report concludes, “no differences have been found that implicate a higher risk to human health and safety from these GE foods than from their non-GE counterparts.” But the committee is also careful to say that there are limits to what we can know. Any new food, whether GE or not, “may have some subtle favorable or adverse health effects that are not detected even with careful scrutiny and that health effects can develop over time.”

The report’s discussion of human health also includes some optimism that both GE and non-GE crops with increased concentrations of some nutrients could have “favorable effects on the health of millions of people.”

Crop Yields

The report distinguishes between the potential yields of crops (that is, the maximum yield, under ideal conditions), and their actual yields (after insects, disease, bad weather, or weeds have their way with them).  There’s no evidence that GE crops have increased potential yields, which had been steadily increasing before GE crops were introduced, and continued to increase afterward.

GE crops can, however, help protect yields from pests.

Pesticide Use

Crops with a built-in organic pesticide called Bt have not just reduced insecticide spraying on the acres they’re planted on, they have, in some cases (like that of the European corn borer), reduced the pest population so dramatically that insecticide spraying has gone down on non-GE acreage.

The report notes, however, that insects can develop resistance to Bt (some have).  To head that off, proper management (including refuges, which are areas where Bt crops aren’t planted so insects don’t develop resistance) is essential, and the report expresses concern about the “lack of compliance with the mandated refuges.” Crops engineered with an insecticide work as a part of a pest-management strategy, but they aren’t, by themselves, the solution to insect problems.

For crops that are tolerant to glyphosate, the herbicide in Roundup, the story gets more complicated. While those crops initially decreased overall herbicide use, the report says those decreases have not been sustained.  The committee also specifically rejects the measurement of herbicide application (kilograms per acre or hectare) as meaningful, because some herbicides are more toxic than others. and suggests that “researchers should be discouraged” from reporting those numbers.

The downside of herbicide tolerant crops is that, “in many locations some weeds have evolved resistance to glyphosate.” The report cites one study that puts the cost of managing glyphosate-resistant weeds at $66/acre for corn and $22/acre for soy, an amount that can sometimes make the difference between a positive and negative gross margin.

Better weed management has to go hand-in-hand with the deployment of herbicide-tolerant plants, the report finds.

Biodiversity and Environmental Impact

The report addressed a varied group of concerns related to how GE crops interact with the environment.  Here are the committee’s findings.

  • There’s no evidence of adverse effects of Bt crops on honeybees.
  • Although crop rotation and crop diversity have been declining since 1987, the report didn’t find a cause-and-effect relationship with GE crops. The committee did note that some GE varieties can facilitate “successful management of very large areas of these crops without rotation.” On the other hand, the committee considered evidence that GE crops could enable crop rotations that would be “prohibitively difficult or expensive” without the weed control that comes with herbicide-tolerant crops.
  • Research has not shown that “suppression of milkweed by glyphosate is the cause of monarch decline,” but researchers disagree about whether glyphosate has any impact on monarchs.
  • ‪Although there has been gene flow from GE crops to wild relatives, “no examples have demonstrated an adverse environmental effect.”
  • The report couldn’t find a clear cause-and-effect relationship between herbicide-tolerant crops and no-till farming practices.

Social and Economic Effects

The report makes the point that, when we’re talking about introducing a new kind of crop into our food system, we have to look beyond matters of human and environmental health, and take social and economic issues into consideration:

  •  ‪Overall GE crops have worked out well, economically, for the farmers who have chosen them, but there’s a lot of variation in outcomes.  Insect-resistant crops reduce loss to insects, and herbicide-tolerant crops “tend to reduce management time.”
  • Benefits of GE crops aren’t always available to small-scale farmers, because of the high price of seed and inadequate access to credit, “among other institutional issues”
  • For small-scale farmers to get the economic gains of GE crops, they’ll often need “institutional support, such as access to credit, affordable inputs, extension services, and markets.”  They may need assistance “improving soil fertility, increasing nutrient availability, and optimizing plant density”
  • Regulatory barriers have raised the price of developing GE crops, which makes it more difficult for the private sector to develop crops that aren’t widely planted. This works against having a diverse selection of GE crops.
  • The report notes that some studies have suggested that GE crops “contribute to farmer deskilling.”
  • It’s important to prevent the inadvertent presence of GE crops in non-GE fields, for both social and economic reasons. “Farmers want the freedom to decide what crops to grow,” and non-GE crops command a higher price.  The committee notes that this is often happening: “many areas are successfully growing organic, non-GE, and GE crops.”
  • One important economic issue is trade disruption.  As different countries approve different GE crops at different times, trading becomes complicated.  “Trade disruptions … are likely to continue to occur and to be expensive for exporting and importing countries.”
  •  ‪The report also tackles the very fundamental issue of trust.  It’s “difficult to capture the cost of a loss of public trust in a product, an industry, or the legitimacy of a regulatory system.”


The report says that regulation of GE crops “should facilitate achieving the maximum societal benefits … at given levels of acceptable risk.”  The committee acknowledges that it’s a tall order, because both risks and benefits vary among crops. NAS is clear that it is the product—not the process—that should be regulated.

Other regulatory issues include:

  • Patents (of both GE and non-GE crops) can limit access by “small farmers, marketers, and plant breeders who lack resources to pay licensing fees or to mount legal challenges,” and there’s disagreement over whether patents facilitate or hinder “knowledge-sharing, innovation, and the commercialization of useful goods.” The report predicts that technology “that is of most use to small-scale farmers or farmers of specialty crops will probably have to emerge from public-sector institutions or from public-private collaborations” because the incentives aren’t there for industry to work on those crops.
  • Although the labeling issue is complex and there are “strong nonsafety arguments and considerable public support for mandatory labeling,” the committee “does not believe that mandatory labeling of foods with GE content is justified to protect public health.”
  • “Policy regarding GE crops has scientific, legal, and social dimensions, ad not all issues can be answered by science alone.”  The values and priorities of all stakeholders have to be considered.
  • ‪Regulators need to be proactive communicators, and “transparency and public participation” are “critically important for appropriate, sound, and credible governance.”
  • “The lack of public access to the health and safety data submitted by developers creates distrust in some stakeholders” because “the public cannot judge for itself the quality, objectivity, and comprehensiveness of the materials submitted.”  While the committee recognizes “the legitimacy of the confidential nature of business information,” it urges as much sharing as possible.

Looking Forward

The report sees an important role for genetic engineering, and “the committee expects that its potential use in crop improvement in the coming decades will be substantial.”  Increased nutrition, better nutrient use, decreased greenhouse gas emissions, and pathogen resistance are just some of the ways GE crops can improve human and environmental health, farmer well-being, and agriculture’s sustainability, it says.

Tamar Haspel is a food and science journalist. She can be reached on Twitter @TamarHaspel.

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