GMOs: Are They Safe? What Are The Pros and Cons?

By: Barry Estabrook  |  July/August 2015
Are GMOs the answer to safer, more efficient farming or are they the poster child for an unhealthy food supply?
Watch: What Does Genetically Modified (GMO) Mean?
For 50 years, plant breeders grappled with a vexing difficulty whose solution was tantalizingly evident, but out of reach. Rice loves to sink its roots into water-saturated soil, but most rice varieties die if the plants are totally submerged for more than a few days. In impoverished eastern India and Bangladesh alone, farmers lose an estimated 4 million tons of rice each year—enough to feed 30 million people—when floodwaters inundate their crops, something that is all too common in the low-lying, monsoon-wracked area, and bound to become even more common as sea levels rise because of climate change. But agricultural experts knew of one ancient, almost forgotten, variety of rice that could survive being submerged for as long as two weeks. Unfortunately, its yields were too skimpy to make it a practical source of food. Decades of trying to cross it with high-yielding rice strains resulted in a series of frustrating failures. It seemed like the genetic traits that gave the rice its ability to survive submersion were intractably linked to those that made it produce low quantities of grain.
“I stood on a farm in Bangladesh and saw how the gene we discovered (which Mackill had introduced into a new rice variety) allowed farmers to triple their yields from flooded fields”
In the mid-1990s, Pamela Ronald, Ph.D., a geneticist at the University of California, Davis, and her two associates David Mackill and Kenong Xu, brought their expertise to the problem and used genetic-engineering techniques and advanced computer programs to discover—out of the 42,000 genes in rice—a single gene that carried the submergence-tolerance trait. They spliced that gene into a high-yielding rice variety that would normally have died in a flood and transplanted the genetically modified seedlings along with unmodified seedlings into a Davis greenhouse plot that they intentionally flooded. Two weeks later, they returned. They noticed that most of the rice plants were weak, spindly, pale and dying, but encountered a few rows of vigorous, bright green plants. Bending over for a closer look, they determined that the survivors were the ones into which they had inserted the flood-resistant gene. Ronald was elated, but her happiest moment came several years later. “I stood on a farm in Bangladesh and saw how the gene we discovered (which Mackill had introduced into a new rice variety) allowed farmers to triple their yields from flooded fields,” she said when I visited her office earlier this year.
Ronald is a trim, fit woman. She rides her bicycle five miles to and from work each day and the diet she and her husband and two teenage children eat is healthy and rarely includes red meat. She is also an evangelist for what she calls “plant genetic improvement.” Listening to her relate the story of her “scuba” rice and how it is helping feed some of the world’s poorest people, I found myself thinking, this is a no-brainer. What’s not to like? How is it that genetically modified organisms (GMOs) became one of the hot-button food issues of our day, sparking furious debate?
On one side are agribusinesses, government agencies and scientists like Ronald. “The consensus that the process of genetic engineering is as safe or safer than conventional methods is stronger than even the consensus that the climate is changing or that vaccines are safe,” she said. The National Academy of Sciences, the American Medical Association, the World Health Organization, the American Association for the Advancement of Science and dozens of other internationally respected groups all agree that the GMOs currently on the market are as safe and healthful as their conventional counterparts.
Yet almost two-thirds of American adults still feel that GMOs are unsafe, according to a survey released this year by the Pew Research Center. The gap between science and public opinion on GMOs is wider than it is on other controversial science, food and public health issues. “Scientists understand the authority of the well-respected, nonprofit global scientific organizations that say genetic modification is safe,” said Ronald. “The public is often not familiar with these leading agencies so instead get much of their information from digital and broadcast media. It is very difficult for the public to navigate this terrain.”
The controversy includes claims by anti-GMO campaigners that genetically engineered crops can increase cancer and chronic illnesses. Plus, they say altered foods can contain unsuspected allergens and be nutritionally deficient. They hold out the specter that the technology is fraught with unknown, potentially catastrophic dangers. Others worry about the environmental damage done by the increased use of herbicides in connection with growing GM crops and that GM farming will perpetuate the evolution of weeds and insects that are immune to pesticides.
Whether these concerns are warranted or not, some major food companies have responded by removing GMOs from their products. Popular products that have gone non-GMO include General Mills original-flavor Cheerios and Post Grape-Nuts. Kellogg’s-owned Kashi has pledged to remove GMOs from at least half of its products by the end of the year and Ben & Jerry’s is phasing out genetically modified products in its ice cream (and supports GMO labeling). Target offers about 70 GMO-free store-brand food products in its stores.

The Safety Debate

GMOs became commercially available to farmers in 1996. (GMO, GE, GM, transgenic and genetic modification all mean the same thing.) Some of the first genetically modified crops introduced were corn, cotton and soybeans. By 2013, American farmers planted GM varieties on about 170 million acres—close to half of the total land used for crops in the country. Roughly 90 percent of the corn and soybeans produced in the United States is GM, the majority of which is used in animal feed and fuel. Virtually all U.S.-grown sugar beets (which are not the same beets you eat) are modified—and account for over half of the sugar produced in the country. Genetically modified ingredients like high-fructose corn syrup and vegetable oil can be found in about three-quarters of the processed foods on supermarket shelves.
Those who say there is no safety problem with GM foods point to the two decades of their widespread use and contend that no studies have confirmed that a human has been sickened by a GM product. They also point to literally thousands of animal studies showing that GMOs are both safe and no different from conventional crops. But most of these studies focus on a specific subset of GMO technology and are too arcane to be understood by nonscientists. They have titles like “Composition of grain… from second-generation glyphosate-tolerant soybean… is equivalent to that of conventional soybean.” Fortunately, researchers have reviewed such studies, often hundreds for a single paper, and produced reports that provide a broader perspective. In a 2010 article for the journal Food and Chemical Toxicology, Wayne Parrott, Ph.D., of the University of Georgia, whose expertise is in plant breeding and genomics, compiled the results of more than 200 papers and concluded that taken as a whole, the research provides a “high level of assurance that such engineered crops [are] safe for food and feed use.” Another review of more than 1,700 studies that appeared in Critical Reviews in Biotechnology in 2014 stated: “The scientific research conducted so far has not detected any significant hazards directly connected with the use [or eating] of GE crops.”
Although many GMO supporters claim that the science on GMO safety is settled, the debate continues. In a 2011 paper, the respected Spanish toxicologist José L. Domingo, who is also the editor-in-chief of the journal Food and Chemical Toxicology, published a comprehensive review of scientific papers addressing the safety of GM foods and plants. He found plenty of disagreement. The numbers of authors saying GMOs were safe and those raising “serious concerns” were nearly equal. Moreover, he noted, most of the favorable studies had been conducted by scientists working at the biotechnology companies responsible for commercializing GM crops.
Then there’s the roster of studies calling the safety of GM crops into question, which opponents draw upon. In 2011, a group of Canadian researchers published a paper in the journal Reproductive Toxicology that found traces of glyphosate in the blood of 69 women living in Quebec, as well as in the fetuses of those who were pregnant. (Glyphosate is the world’s most-used weed killer, marketed by Monsanto as Roundup and Dow AgroSciences as Durango DMA; it’s commonly used in conjunction with GM crops.) They speculated that the pesticides came from the meat of livestock fed GM crops. And ultimately concluded that “given the potential toxicity of these environmental pollutants and the fragility of the fetus, more studies are needed.” Another study found that Brazil-nut genes inserted into soybeans could have caused allergic reactions if people with nut allergies consumed the soy. The seeds, however, never made it to the open market. A study revealing that rats fed corn modified to resist Roundup suffered more tumors and died earlier than rats fed non-GMO corn was published in Food and Chemical Toxicology in 2012. The paper had been reviewed and approved by a panel of scientists prior to publication, but the editors retracted it after pro-GMO forces attacked the researchers’ methods and conclusions. Those condemning the study claimed that the type of rats used in the experiment were prone to tumors and too few rats were studied to draw definite conclusions. Supporters of the research point out the study used the same number and type of rats used by seed companies in studies that show GMOs to be safe.
Michael Hansen, Ph.D., senior scientist at the Consumers Union, told me that another problem is that most studies showing GMOs to be safe last only 90 days—a short span of time even in the life of a lab rat. Long-term studies over the entire natural lifetime of experimental animals (around two years for a rat) are needed, according to Hansen. “No one is saying that GMOs cause acute problems,” Hansen said. “You are not going to fall over dead or get sick the day after eating a chip made out of GMO corn, but there simply haven’t been adequate studies of their long-term effects. Before they can be shown to be safe, those studies need to be done.”
When I asked if he could point to any studies that showed evidence of GMOs harming a human’s health, Hansen said that such studies would be virtually impossible to conduct. “You would have to track a group of people who had been exposed to GMOs and a group who had not.” The absence of such studies, he said, means that scientists really don’t know if GMOs are safe. “Saying there’s no evidence really doesn’t mean anything unless you’ve actually looked for evidence.”
The Food and Drug Administration (the government agency charged with protecting human health through the regulation and supervision of food safety, supplements, pharmaceuticals, etc.) has approved GMOs currently in the marketplace, but Hansen takes issue with the basis of the FDA’s approach. In 1992, before the large-scale introduction of GMOs to American farms, the FDA concluded that it was not aware of any information showing that GM techniques pose any “different or greater safety concerns than foods developed by traditional plant breeding.” They looked at components such as protein, fat, oil and carbohydrate, and found GM food crops were the “same as or substantially similar to” their conventional counterparts and therefore did not require safety reviews. “The key factors in reviewing safety should be the characteristics of the food product rather than the fact that new methods are used [to develop the products],” the FDA wrote. As a result, formal safety tests are not mandatory for new GMO products to get FDA approval. Companies can voluntarily submit studies to the FDA for “safety consultations,” but even in such cases, the FDA doesn’t do its own tests. It relies instead on conclusions reached by the companies that produce and want to market the new GM products. And those reports are considered to be company secrets, so the FDA does not make them public. A typical letter of approval from the FDA granted to Monsanto reads:
“It is our understanding that Monsanto has concluded that corn grain and forage derived from the new variety… do not raise issues that would require… approval by the FDA.” (Emphasis added.)
“Voluntary consultations with industry do not constitute a true safety assessment,” said Hansen. But Monsanto contends that GM crops are more than adequately inspected. In an email, Tyson Pruitt, a company spokesman, wrote, “Biotech crops undergo more testing and oversight before commercialization than any other agricultural products, including conventional (or nonbiotech) crops. In the U.S., every biotechnology product has to be submitted to two or more of the following agencies for approval: FDA, U.S. Department of Agriculture and the EPA.”

The Environmental Impact

The vast majority of GMO crops do one of two things. They either create herbicide resistance, allowing farmers to chemically kill weeds but not damage their crops, or they cause plants to produce a toxin that kills some insects (a “built-in” insect resistance). There are environmental and human health benefits (and drawbacks) to both of these technologies.
GMOs can save human lives by reducing dependency on pesticides that are highly toxic to humans. In developing countries where farmers often do not understand the dangers of insecticides or cannot afford protective clothing or safe application devices, about 250,000 fieldworkers die each year from pesticide poisoning (this figure includes suicides by intentional poisoning). Use of these chemicals is reduced dramatically when land is planted with GM crops carrying genes that cause the plants to produce their own insecticide, eliminating the need to spray dangerous chemicals. The gene actually comes from a soil-dwelling bacterium called Bacillus thuringiensis (Bt) and produces a naturally occurring chemical that destroys the digestive tracts of certain insects (particularly the devastating pest, western corn rootworm) but is nontoxic to mammals, birds, bees and even earthworms. By planting Bt corn, U.S. farmers have reduced chemical insecticides tenfold. Today, less than 10 percent of U.S. corn farmers apply insecticide at all.
Plants engineered to survive herbicides may benefit the environment by enabling farmers to adopt so-called no-till practices. Traditionally, farmers plow (till) the top eight or ten inches of soil on their fields, turning it over and burying stubble from the previous season’s crops, along with weeds, insect larvae and other soil-dwelling creatures that hinder crop growth the next season. Exposed to sun, wind and rain, the bare fields are prone to erosion, and earthworms and other organisms vital to the health of plants die. With no-till, the old crops’ residues are allowed to stay in place and new seeds are planted in narrow troughs sliced into the earth. This method means the soil is not disturbed, so water absorption increases, preventing evaporation and boosting populations of soil fauna. Carbon from the previous season’s crop residues stays buried in the soil (unlike when you till) and releases slowly into the air, which reduces planet-warming carbon in the atmosphere. This is called carbon sequestration. Although the amount of no-till acreage in the United States has steadily increased annually to now comprise about 34 percent of all cropland (thanks largely to herbicide-tolerant GMOs), not all farmers planting herbicide-resistant GMOs are adopting no-till practices (the biggest obstacle being high costs for no-till farming equipment).
Unfortunately, there are harmful effects to both herbicide-resistant and insect-resistant crops. Markedly higher amounts of herbicide need to be applied to no-till fields to kill weeds that would have been effectively controlled by plowing and cultivation. U.S. farmers’ annual application of glyphosate has mushroomed. Since 1996—when herbicide-resistant crops were introduced—average herbicide use has about doubled in soybeans and more than doubled in cotton. In 2014, enough glyphosate was applied to spray nearly two-thirds of a pound on every cropland acre in the country. “No herbicide in history has come remotely close to glyphosate in terms of total pounds applied in the U.S., or globally,” says Charles Benbrook, research professor at Washington State University’s Center for Sustaining Agriculture and Natural Resources. Earlier this year, the World Health Organization (WHO) said the chemical is “probably carcinogenic to humans” after reviewing research indicating higher than normal cases of non-Hodgkin lymphoma among farmers who used glyphosate and experiments showing that rats and mice fed food contaminated with the herbicide developed tumors.
In a press release disputing the WHO’s conclusion, Philip Miller, Ph.D., Monsanto’s vice president of global regulatory affairs, said, “All labeled uses of glyphosate are safe for human health and supported by one of the most extensive worldwide human health databases ever compiled on an agricultural product.” He also said he did not know how WHO “could reach a conclusion that is such a dramatic departure from the conclusion reached by all regulatory agencies around the globe.”
But there is agreement among experts that saturating farm fields with glyphosate has led to the evolution of herbicide resistance in at least 14 weed species in the U.S. To kill the “super weeds,” farmers have resorted to more powerful alternatives, such as the herbicide 2,4-D, a component of the Vietnam War-era defoliant Agent Orange, which has been linked to cancer and reproductive problems. Seed companies have already introduced GM crop varieties engineered to survive being sprayed with 2,4-D, which GMO opponents say will result in a surge in 2,4-D’s use similar to the rise in application of glyphosate.
Similarly, insects are developing immunity to Bt. In 2009, Aaron Gassmann, Ph.D., an Iowa State University entomologist, discovered that corn rootworm in Iowa had begun to develop resistance to the pesticide. Rootworm Bt resistance has since developed in other states as well. The resistance also impacts many organic growers, as they are permitted to spray—and, thus, rely on—Bt insecticide (a natural pesticide) to control common pests, such as cabbage worms, on their crops.

Common Ground

All the controversy left me wondering if there was any common ground between the pro- and anti-GMO camps. After I interviewed Pamela Ronald, I drove a short distance to UC Davis’s 16-acre organic student garden. As I got out of my car, I saw an ancient orange tractor chugging toward me, a cloud of dust billowing behind it. The driver climbed down and proffered a calloused hand. He looked every inch an organic farmer, from his sun-reddened face in the shadows cast by a wide-brimmed straw hat to his stained Carhartt jeans and muddy rubber boots. His name was Raoul Adamchak. He teaches students about organic farming and manages the market garden—which is strictly non-GMO. He is also married to Pamela Ronald.
At the very least, I imagined that their perspectives on GMO technology would spark some lively dinner conversations. But Adamchak insisted that peace reigned around the family table. “We’re both interested in improving the sustainability of agriculture. I’m organic because I do not like to use toxic, synthetic pesticides and don’t want to be in an environment where they’re used. But 99 percent of American farmland is nonorganic. If there are GE crops that let those farmers reduce pesticide use or adopt environmentally beneficial no-till practices, then everyone benefits.”
To that, Ronald later added, “We both have the same goal—an ecologically based system of farming. I believe that feeding the growing population without further destroying the environment is one of the greatest challenges of our time. And genetic modification has a role to play.” Ronald’s own work is an example of how genetically modified crops could help meet that challenge—she has engineered strains of rice to resist bacterial disease and improve yields by 40 percent.

A GMO-free Day

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The Promise of GMOs

Consumers in the U.S. stand to benefit from other newly introduced GMOs. Early this year federal regulators gave official blessing for modified versions of potatoes that do not bruise easily and produce less of the potentially carcinogenic chemical acrylamide when deep-fried. This year also saw the approval of GM apples that don’t brown when sliced, which could make a healthful product convenient—and more visually enticing—in school cafeterias and fast-food restaurants. Hawaiian papayas are available today because geneticists engineered them to resist a virus that had threatened to wipe out the industry in that state.
Hundreds more GM foods have been developed by researchers and companies but have not yet entered commercial production. They include pink pineapples that produce the good-for-you antioxidant lycopene, super-fast-growing salmon that need less precious marine-feed resources to grow and soybeans that yield oil that’s high in heart-healthy omega-3 fatty acids. There’s also Golden Rice, where genes from a soil bacterium and corn were put into traditional rice so that it produced beta carotene, a precursor to vitamin A. If rice-dependent developing countries grew and ate Golden Rice, it could help prevent as many as 2 million deaths and 500,000 cases of blindness each year.
“GMOs are not UFOs”
“GMOs are not UFOs,” Ronald said. “Every crop has to be looked at on a case-by-case basis. You can’t generalize about genetically modified papayas and Golden Rice. They have completely different traits. They benefit completely different populations. What scares me most is that the poorest people who most need the technology may be denied access because of vague fears and prejudices of those who have enough to eat.”
Her assertion points to a middle ground in the GMO debate. There are profound benefits to growing rice that allows a mother in the Philippines to spare her children from blindness or a farmer in Bangladesh to raise rice plants without exposing himself and his family to toxic insecticides or a Hawaiian papaya producer to stay in business. On the other hand, the direct benefits to consumers are less clear when you look at crops like corn and soy that make up the majority of GMOs grown in the U.S. today. Perhaps the federal agencies charged with protecting our health should require the multinational corporations selling GMOs to conduct rigorous, foolproof and thoroughly transparent testing before allowing GMOs to leave labs and enter the food supply. Better yet, perhaps the government agencies should be responsible for the testing. Shouldn’t they take steps to prevent herbicide-resistant weeds and pesticide-tolerant insects from entering the environment? Until then, maybe consumers shouldn’t be criticized for wanting GMOs to be labeled.
Barry Estabrook is a three-times James Beard Award-winning journalist. His most recent book is Pig Tales: An Omnivore’s Quest for Sustainable Meat (W.W. Norton & Co., May 2015).