GMO Foods: Good or Bad?

Written by Atli Arnarson, PhD on September 27, 2015

Genetically modified foods (GMOs) are highly controversial.

Yet, despite the debate, GMOs are found in all sorts of food products — often without labels.

Therefore, it's important to understand the science behind these foods.

This article explains what genetically modified foods are, and how they can affect your health.

GMO stands for "genetically modified organism."

The term is generally used for food that has had its genes changed using biotechnology.

Using genetic modification, scientists are able to produce new varieties of plants with certain qualities, such as being more resistant to viruses or pesticides.

To understand how this works, knowing some basic principles of genetics is required.

Basics of Genetics

Genetics is a scientific field that studies genes and heredity.

Genes contain instructions about how to make living organisms. These instructions are basically codes consisting of DNA, which is found inside cells.

Genes tell cells what to do, ultimately determining how organisms look and function. All living things inherit genes from their ancestors, which is why we look similar to our parents.

However, genes are not entirely stable. They are prone to changes called mutations.

This is part of the reason why each individual has unique physical features. The genes are slightly different between individuals of the same species.

Bottom Line: Genes contain information on how living organisms should look and function. Genes vary slightly among individuals of the same species.


Evolution is a term that describes changes in organisms over many generations.

These changes happen because genetic makeup varies between individuals, even for organisms within the same species.

Evolution is usually a very slow process, and is determined by adaptations to specific environmental conditions.

Here is a simple example:

  • A species of plants is found on an island. The island has a wet climate and these plants have adapted to growing in wet conditions.
  • Gradually, over thousands of years, the climate changes from wet to dry.
  • Because of individual variability, some of the plants are, by chance, more tolerant to dry conditions than the others.
  • These plants survive, whereas the less drought-tolerant plants are more likely to die before they can produce seeds.
  • The end result is a plant population that has adapted to living in dry conditions.

This is called natural selection, and is where the phrase "survival of the fittest" comes from. The genes that are best suited for survival in the environment get passed on to future generations.

Bottom Line: Genetic variability drives natural selection. Some individuals are more likely to survive and reproduce, which over time may change the species.

Selective Breeding

Humans have used these natural principles to create various breeds of domesticated plants and animals. This is known as selective breeding.

Selective breeding is a faster process than evolution. It is based on choosing individuals that have desirable features and breeding them together.

For example, cows have been selectively bred to produce more milk, and apple trees have been selected to produce bigger fruit.

With genetic modification, this process has been made faster and more precise.

Bottom Line: Selective breeding involves choosing individuals with desirable features and breeding them together.

Genetic Modification

Genetic modification is a technique that allows scientists to alter the genetic material of an organism.

This is usually done by transferring a gene from one organism to another, giving it new traits.

For example, genetic modification can be used to make plants more resistant to diseases or pesticides.

It can also be used to increase a plant's nutritional value, allow it to grow faster or make it taste better. The possibilities are endless.

Here are some examples of genetically modified (GMO) foods:

  • Herbicide-resistant corn and soybeans: Corn and soybeans were modified to tolerate the herbicide glyphosate, found in Roundup. This allows farmers to spray their fields with powerful herbicides to kill off weeds.
  • Virus-resistant papaya: In Hawaii, papaya was genetically modified to be able to withstand the ringspot virus.
  • Golden rice: Swiss scientists developed golden rice, a type of yellow rice that produces beta-carotene, an antioxidant that the body can turn into vitamin A (1).

Other crops that are often genetically modified include rapeseeds (used to make canola oil) and cottonseeds.

Bottom Line: Genetic modification allows scientists to transfer genes between organisms. This technique is more precise than selective breeding, and offers endless possibilities.

The amount of GMO food on the market is increasing worldwide.

However, the exact amount of GMOs you may be eating is difficult to estimate. This is because these foods are not always labeled as such.

In the US, GMO foods do not need to be labeled. Conversely, the European Union requires all GMOs to be labeled.

There are actually far fewer GMO foods available in Europe. These foods are much more readily available in US markets.

About 70–90% of GMO crops are used to feed livestock, and more than 95% of all food-producing animals in the US consume GMO feed.

If you eat soybeans, especially processed soy products, it is likely that they come from a GMO crop. More than 90% of all soybeans are genetically modified (2).

Keep in mind that soy, corn and canola are incredibly common in processed foods in the US. If you eat processed food, then you are almost definitely eating some genetically modified ingredients.

Bottom Line: GMO foods are generally not labeled in the US. Most processed foods in the US contain soy, corn or canola, so if you are eating processed foods then you are probably eating some amount of GMOs.

GMO food is highly controversial.

People's opinions of GMO foods are often based on ethical, philosophical or religious views.

Scientific misconceptions also frequently affect people's beliefs (3).

However, there are plenty of unanswered questions regarding large-scale genetic modification and GMO agriculture.

Some scientists are concerned about the potential environmental impact and sustainability. Meanwhile, others believe that genetic modification may have beneficial environmental effects in the larger scheme of things.

Supporters of GMO foods also argue that genetic modification may be necessary to prevent food shortages as the world's population continues to grow.

However, most people who avoid GMOs are doing so because they believe these foods to be unhealthy.

Bottom Line: Genetic modification is a very controversial subject and there are many unanswered questions.

GMO foods cannot be generalized as either healthy or unhealthy.

It depends entirely on individual genetically modified crops, which should be assessed on a case-by-case basis (4).

Some people have pointed out that transferring a gene from an allergenic food crop, such as peanuts, could make the GMO food allergenic as well. While this is a possibility, safety testing should prevent such products from going on the market (5).

That being said, the risks associated with GMO foods are considered to be very low. They are no greater than those arising from traditional genetic manipulation through selective breeding (6).

To date, there is no evidence suggesting that GMOs cause harm in humans (7).

Likewise, most animal studies suggest that GMOs are safe (2, 8, 9).

Yet, despite the general lack of evidence against GMO foods, there is considerable public opposition to them and the debate continues.

This may be partly due to general distrust of biotech companies. There is also a potential conflict of interest in many scientific studies (10, 11).

Bottom Line: GMO food itself cannot be generalized as unhealthy or toxic. There is no good evidence saying these foods negatively impact human health.

Even though there is no good evidence showing that GMO foods themselves are unsafe, there are some other factors to consider.

A few animal studies suggest that herbicide-resistant crops sprayed with glyphosate (Monsanto's Roundup herbicide) may cause adverse effects (12).

A notable study from 2012 showed that GMO corn that had been sprayed with glyphosate promoted the formation of cancerous tumors in rats.

The authors suggested that the tumors were a result of the toxic effects of glyphosate and/or the genetic modification itself (13).

The results of the study were controversial and heavily debated. In fact, the original paper was retracted, but published in a different journal later the same year (14, 15, 16).

A few other animal studies and test-tube experiments have found signs of adverse effects when testing GMO corn and soybeans sprayed with glyphosate.

These studies suggest that trace amounts of the herbicide may be causing harm, rather than the genetic modification itself (17, 18).

Bottom Line: While GMO foods themselves cannot be classified as unhealthy, other related factors may cause adverse effects. The herbicide glyphosate (Roundup), which is sprayed on some GMO crops, may be harmful to health.

The available evidence indicates that GMO food is not harmful to human health.

However, the health effects of spraying GMO crops with the herbicide glyphosate is still a matter of debate.

Nonetheless, there is no good evidence that genetic modification itself causes foods to become unhealthy or toxic.

An evidence-based nutrition article from our experts at Authority Nutrition.

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