AgBioResearch

Questions of safety are often answered by way of a comparison – “Travelling in an airplane is safer than driving in a car.” Understanding is gained through familiarity with the object of comparison. When it comes to genetically modified, or GM, foods, the comparison to non-GM foods is not only illustrative of safety but a key part of determining it.

In the United States, the Food and Drug Administration (FDA) determines the safety of GM foods through a rigorous series of tests based on the concept of “substantial equivalence” – a process designed to demonstrate that the GM or novel food version of a food (or crop) is as safe as the traditionally bred non-GM version. If there is no significant difference, the GM food is considered safe for consumption.

However, if something is “as safe as” something else, is it accurate to say – it is just as unsafe?

“No food, GM or non-GM, is absolutely safe,” explained Robert Hollingworth, professor emeritus of the Michigan State University (MSU) Department of Entomology and Institute for Integrative Toxicology. “However, it is very close to the universal conclusion of every expert who has evaluated it, that the GM crops we have at the moment are as safe to consume as the standard crops that we have been consuming for years.”

It might come as a surprise to many that conventional (non-GM) whole foods are not tested for safety. The absence of testing is partly due to the assumption that the foods we have been eating for generations are inherently safe. Another reason is that safety-testing whole foods is substantially different and more challenging than testing single chemicals such as drugs and pesticides.

The difficulty of testing whole foods

“You really cannot adequately test whole foods, the way that you can test single chemicals,” said Hollingworth. “One of the main criteria when chemical testing is that you give the test animals (typically mice or rats) at least one dose that is much higher than you’d expect any one human being to ever get. Test animals can be less sensitive than humans so low levels that could be safe for the mouse would not be safe for you or me. So, a high dose is a key part of the process and you can’t do that with whole foods – you can’t feed 10 times the normal amount of apples to a mouse.

“Also, crop plants contain a large variety of chemicals that can vary considerably between different varieties of the crop, the conditions under which it is grown and stored, and how it is cooked. This makes interpreting safety tests by feeding any food to animals very challenging.”

There are many non-GM crops in the food supply that contain naturally occurring, potentially toxic chemicals. These typically serve to defend the plant against insects and predators. The low levels of chemicals present in these crops today are the result of traditional selective breeding practices over thousands of years.

“You can use conventional breeding methods which may change the genetics of a crop far more than it would be changed by a GM technique,” said Hollingworth. “There are examples of people breeding varieties of potatoes with high levels of glycoalkaloids that were actually dangerous to consume – glycoalkaloids are about as toxic as strychnine. People found out about it and stopped growing them. But it is perfectly possible to do that kind of thing and you do not have to answer to anybody before putting it on the market.”

Conventional breeding practices have resulted in the wide range of fruit varieties available in supermarkets and grocery stores today, such as Fuji, Honeycrisp and Red Delicious apples. The difference in taste, texture, size and color between different varieties are the result of significant changes to the original genetics of the fruit.

Selectively breeding food crops to be more appealing in appearance and in taste has also involved mutation.

“More crops than you would imagine, in the supermarket today, were actually bred by mutagenesis. That is either treating the seeds with mutation-causing chemicals or blasting them with radiation,” said Hollingworth. “Ruby Red Grapefruit is an example and some of the barley strains that are used, even to produce organic beer, were produced in this way. It is quite common.”

Despite the extent of change caused by the mutation, mutagenesis is not classified as genetic engineering, and consequently, not subject to the same laws and regulations as GM foods. Even though the mutation can cause bigger changes to the genetics of the plant than the intentional changes achieved through genetic engineering.

“With mutagenesis, often the majority of things that happened were bad and so they would get thrown away, but once in a while something that was positive, like having no seeds or being shorter and therefore easier to harvest resulted and those were eventually released on the market, and without anybody asking a question,” Hollingworth said. “Technically, at least, today you can still do that.

“Now that doesn’t necessarily mean that we shouldn’t be interested in what’s going on with the GM. It’s just that we have a very remarkably double standard in some of these things.”

Classification of GM foods

A food is classified as GM when its genetic makeup or genome has been modified in some way using biotechnology. Both traditional selective breeding practices and mutagenesis cause changes in the genome. However, while foods produced from all these approaches are similar in that the genome was altered, there is one branch of GMOs that are uniquely different from the mutant grapefruit and fruit varieties consumers are familiar with – transgenic GMOs.

A GMO is transgenic when it contains a gene from a different species. This allows for certain traits from one species of plant, for example, to be selectively transferred to another species. Golden rice is one example of a transgenic GM crop. Genes from corn and harmless bacteria were added to rice to greatly increase the amount of beta carotene in it.

Beta carotene (which turns the rice yellow, hence the name) is an ingredient the human body needs to make vitamin A. Vitamin A deficiency causes 500,000 cases of blindness in children every year, according to the World Health Organization, and many of these children will die. Golden rice can help prevent this.

Felicia Wu, John A. Hannah distinguished professor in MSU’s Department of Food Science and Human Nutrition and Department of Agricultural, Food, and Resource Economics, said food allergies are one concern people have about transgenic GM foods in particular.

“Anytime you introduce a novel gene into an organism, you allow it to encode for a new protein,” she said. “Proteins are rarely toxic and they are rarely carcinogenic, but they can be allergenic. Everything to which we’re allergic in our food or our environment is a protein. So a real concern when these GMOs first came out was that we were introducing new potential allergens into the food supply.”

GM foods are tested in a variety of ways for their potential to cause allergies, including a gastric acid simulation to see how easily the novel food would be digested by humans. According to Wu, if something is digested quickly in the human gut (within 90 seconds), it is very unlikely that it is going to cause an allergic response. If it lasts longer than that, Wu said it could be an allergen.

In 1992, the FDA made a policy decision that a GM food was not required to be labeled as “GMO” if the novel food was not materially different from its conventional counterpart. For consumers with food allergies, this was a serious concern, given the potential for new allergens in transgenic crops.

“Some people need to avoid shrimp, lobster, and crab because of allergies,” Wu said. “Others with allergies know they need to avoid peanuts, dairy, or eggs, and therefore we look on food labels to find out if a product contains these. But if GMOs don’t have to be labeled, as is currently the case in the United States, then nobody knows if they are eating a protein to which they could be allergic. That was a concern of mine when I first started doing research on GMOs.”

Skepticism abounds

When first studying genetically modified crops in the early 2000s, Wu said she was skeptical.

“At the time, I didn’t understand why we needed genetically modified crops,” she said. “I thought we had done perfectly fine for thousands of years with traditional agriculture using conventional and even relatively newer hybrid breeding techniques.”

Wu cites one example in particular, StarLink, a GM corn variety approved by the U.S. Environmental Protection Agency in 1998 for animal feed. It was not approved for human consumption because of its poor gastric acid test results, which could indicate allergic risk. In 2000, StarLink was identified in taco shells and corn dogs. The products were recalled, and production of Starlink ceased. Now any food crop, even if only intended to be used as animal feed, must also pass tests for human consumption.

“When the news came out that there was this type of genetically modified corn (StarLink) that wasn’t supposed to be in food but had turned up in taco shells and corn dogs, the public was scared about it,” Wu said. “I remember as part of my dissertation, I did a survey in Pittsburgh about what people thought about the health effects of GMOs. You could tell that they were a little bit afraid even when they were joking, they said things like ‘Am I going to grow a third arm?’ and ‘Will my hair turn green?’”

Two decades later, despite an international scientific consensus, concerns about the safety of GM foods persist. Hollingworth thinks this concern can be explained in part by the combination of consumers’ lack of understanding of biotechnology and little incentive for the majority of consumers to choose GM foods over conventional ones.

“I think the typical U.S. consumer can’t see any real immediate benefit to them [GM foods]. The benefit is almost all going to the producer in terms of ease of production and cost savings,” he said. “And if you have no understanding of the technology – and most people have none –you have no way to work out if what you’re hearing about GM foods being dangerous or being safe makes sense because you have no context to put it into.”

For Wu, the benefits of certain GMOs to the consumer became clear when, in her own research, she came across findings from Iowa State University revealing that transgenic Bt corn had lower levels of mycotoxins than conventional corn. (Bt corn gets its name from the genetic modification it undergoes to introduce Bt toxin, a naturally occurring insecticide made by the bacterium Bacillus thuringiensis, into it.) Mycotoxins are chemicals produced by fungi when they colonize crops such as corn, wheat, and peanuts, and can be very toxic to humans. For example, aflatoxin is a specific mycotoxin that can cause liver cancer.

“Mycotoxins are in food supplies worldwide. We can’t completely eliminate them from our food, so the FDA regulates them in the U.S.,” explained Wu. “For aflatoxins, 20 parts per billion are allowed in corn, peanuts and peanut products, as well as almonds and pistachios. That means 20 micrograms of aflatoxin for every kilogram of food, which isn’t much. However, there is a cumulative effect because the more you are exposed to any carcinogen, the greater the risk. Aflatoxin directly damages our DNA.

“In studies done all over the world, Bt corn has lower levels of mycotoxins than conventional corn. In the U.S., that means that corn growers have economic benefits from planting Bt corn. In other parts of the world, where mycotoxins are not as strictly regulated, planting Bt corn could mean improved human and animal health. Aside from cancer, mycotoxins have also been associated with growth impairment in children.”

While the beta carotene in golden rice might not strike the average U.S. consumer as a strong enough incentive to explore GM foods and learn more about biotechnology, a lower risk of cancer and increasing the likelihood that children grow up healthy and strong just might.

‘Gene silencing'

The potential for biotechnology to take GM foods beyond “as safe as” to “safer” doesn’t stop with transgenic methods. The cellular mechanism of RNA interference (RNAi) is one biotechnology that doesn’t involve the insertion of a gene to produce a new protein, and as a result, eliminates any risk of introducing a new allergen into the food supply.

“I am part of a USDA project right now in which my colleagues are trying to develop a type of corn that uses RNAi to confer host-induced gene silencing (HIGS),” said Wu. “This allows the corn to sense when a fungus has infected it, and the corn will be able to turn off certain genes in the fungus that produce aflatoxin, such that it could still be infected by the fungus but now there is no aflatoxin.”

RNAi is often referred to as gene silencing, since the process turns off specific gene expressions. The approach has been used to create the non-browning Arctic apple varieties that are sold in the U.S. As her ongoing research attests, Wu said the benefits of gene silencing to consumers can go well beyond cosmetic.

“When you think about the possibilities there is so much potential. And there is no novel protein, like there is in traditional GMOs; you are just tweaking with genes and making the genes do things that they had not done previously,” said Wu.

“You could now apply biotechnologies to crops so that they produce particular vitamins, particular nutrients. They could have benefits to farmers and consumers. They could withstand drought. They could do all kinds of things. As long as they’re proven safe, they could be amazing.”