Author | Chris Kresser Genetically modified foods (GMOs) have been popular in the news lately ever since California failed to pass Prop 37, which would have required the labeling of GMO ingredients on all products sold within the state. While California may be setting the stage for the discussion of future labeling of GMO foods in our country, currently there is no regulation anywhere in the United States requiring the disclosure of GMO ingredients to consumers. This is in contrast to countries such as those in Europe and South America, who highly regulate the cultivation and sale of genetically modified crops and often require the labeling of foods that contain GMO ingredients (12). In America, unless you buy certified non-GMO food, there is no way to know if your food contains GMOs or not.

So why does it matter if our food contains GMOs? You may have heard from various media sources that genetically modified foods are perfectly safe and there is no evidence to suggest any long term risk from their consumption. On the contrary, there has been some evidence suggesting potential health risks caused by these foods; even scientists within the FDA itself have repeatedly warned that GM foods can create unpredictable, hard-to-detect side effects, including allergies, toxins, new diseases, and nutritional problems. (34) With so much conflicting information, it’s hard to tell fact from fiction. Are GMOs safe for human consumption, or not?

What is Genetic Modification?

Genetic modification involves the transfer of genes from one species of plant or animal to another, using techniques that can cause mutations in the genome that may have unintended consequences for the crop’s safety. (5) The imprecise rearrangement of genes can create new proteins in these plants that may trigger allergies or promote disease. (6) Our immune systems often do not recognize these new proteins and may mount an immune attack against them if they enter our bloodstream intact. These unintended gene transfers, along with those that are intended, can lead to significant changes in gut and immune function, and may have long-term consequences that are not yet known to the scientific and medical communities.

In genetically modified corn and cotton, a gene from a bacteria called Bt (Bacillus thuringiensis) is inserted, which causes a pesticidal toxin to be produced in every cell of the plant. This Bt-toxin kills insects that eat the plant by breaking down its gut lining and killing the insect from septicemia caused by the ensuing blood infection. (7) While this toxin has not been proven to be toxic in this way for humans and other mammals, several recent studies have suggested this toxin could have effects on immune health, gut health, liver and kidney function, and fertility.

The potential dangers of GMOs

The gut is most susceptible to the potential dangers of GMO consumption. Bt toxin produced by GMO corn has been shown to significantly alter immune function in mice, and may cause disrupted immune function in the gut. (8910) One study suggested that Bt toxin has toxic effects on human cells in vitro, causing them to die prematurely. (11) This could cause damage to gut endothelial cells if the toxicity is found to occur in vivo. The potential intestinal effects of GMO consumption go beyond Bt toxin. Some argue that gut bacteria are capable of acquiring DNA sequences from GM plants, which could lead to the development of antibiotic resistance in those microbes. (12) It’s not yet fully understood what proportion of the GM genes are able to be transferred to gut microbiota.

There have been effects of GM corn found on organs outside of the intestinal system as well. Analysis of Monsanto’s own research and independent research by a lab in France determined that mice and rats eating Bt-toxin producing corn sustained liver and kidney damage. (1314) Other harmful effects were also noticed in the heart, adrenal glands, spleen and hematopoietic system of these GM corn-fed rats. Bt toxin has also been demonstrated to reduce fertility in mice, with fewer offspring being produced than by mice fed on natural crops. (15) While these are small, preliminary studies, it’s worth investigating the effects GMOs can have on other organs besides the intestines.

Since the research is in its infancy, GMOs may have associated health risks that we do not fully understand. The organization known as The Institute for Responsible Technology has developed a list of potential hazards of GMO consumption, providing a list of references for each health risk discussed. They have amassed a great deal of support for their position that GMOs are dangerous, and much of their information comes from research studies, clinical experience from doctors, and anecdotal evidence from farmers and parents of children who thrived on a GMO-free diet. (Unfortunately, the website’s statements exaggerate the findings of several studies, so it’s best to be a critical thinker and take the information with a grain of salt.)

Why is there still controversy?

Recent reviews have proposed a different story when it comes to GMO safety, arguing that the bulk of the evidence demonstrates no health risks associated with GMO consumption. (161718) These reviews found GMOs to be generally safe with no multigenerational effects, but also recommended that more research continue to be performed on the health effects of GMO consumption in mammals. It’s interesting to note, however, that the majority of the studies considered by these reviews had been conducted by biotechnology companies responsible for commercializing these GM plants; this conflict of interest could have an effect on the reporting of certain data. That said, there’s no denying the fact that independent critical reviews have so far found GMOs to be safe in food.

Unfortunately, credible research demonstrating the potential dangers of GMOs is not only sparse, it is also inconsistent. While many scientists argue that GMOs are unsafe for human consumption, there are many more scientists who suggest that the evidence to date has not found any significant health risks from ingesting GMOs. It’s impossible to tell at this point who has the right answer, and it’s unnerving that there is so much controversy over the safety of a food product that is present in 60 to 70 percent of processed foods found in grocery stores. (19)

A verdict on GMOs?

There hasn’t been nearly enough research performed on GMOs to make an informed decision on their safety. However, lack of proof is not proof against. While the available evidence is still mixed, it seems likely that genetically modified foods could have an effect on the immune response as well as the permeability of the gut. Whether or not this leads to an increase in disease is yet to be determined. However, if regular consumption of GMOs is able to cause leaky gut, it could play a role  in the recent dramatic rise in obesitydiabetesallergiesautoimmune disease, and infertility in our country.

I’m no conspiracy theorist, but I think there is enough inconsistency in the available evidence to support the removal of GMOs from your diet. Fortunately, purchasing certified non-GMO or organic foods and eating a whole-foods or Paleo diet will allow you to steer clear of most GMO foods on the market. Until more legitimate research is conducted, I believe it’s better to be safe than sorry and avoid genetically modified foods as much as possible.