Questions & Answers

Do genetically engineered foods affect health?

In short, no one knows for sure, despite almost 20 years of growing genetically engineered (GE) crops.

In order to answer this question, scientists who are independent of the biotech industry and funded by government science agencies will need to do three things on several different GMO crops and the foods derived from them:

  1. Conduct long-term feeding studies involving several species of experimental animals.
  2. Design and carry out human feeding studies over at least a few years in order to identify any subtle impacts on health, metabolism, development, the immune system, and reproduction.
  3. Carry out epidemiological studies on human populations exposed to GE proteins and the pesticides associated with GE crops, and compare them to similar populations not exposed to them, or exposed much less frequently.

An additional complication is that there are many types of GE plants and many traits moved into GE plants. Some – the so-called “Roundup Ready”® crops – are engineered to tolerate spraying with the herbicide glyphosate.

Other GE crops include a trait that allows plants to produce inside all of its cells a natural, bioinsecticide called Bt toxin. These crops are often referred to as “insect protected” or “Bt-transgenic.” Some GE crops express both herbicide-tolerant and Bt-insect protected traits.

One brand of GE corn – SmartStax – expresses eight traits: two that confer tolerance to herbicides (glyphosate and glufosinate) and six that express different strains of Bt toxin.

Unfortunately, no GE crop or food has been tested fully as outlined above to rule out or identify human health risks. We hope that the US government will soon recognize the vital importance of doing so, especially now that GE crops play such an important role in our food system.

At this time, the closest we can get to our ideal data set is to assess the few dozen long-term (i.e., at least two years) animal feeding studies whose results have been published in top-notch, peer-reviewed science journals.

Our ideal feeding study is one where animals are divided into groups. The control group receives a ration composed of the same types of foods and the same amount of calories as the treatment group (or groups). The only difference between the rations is that one or more of the types of foods it contains comes from a GE crop that is otherwise identical to the control crop.

It is difficult, and costly, to design and carry out these long-term feeding studies in a way that isolates the impact of the GE crop on various parameters of animal health and performance.

In the experiment described below, MON810 GE corn was used. This corn is genetically modified to produce the insecticidal Bt toxin Cry1Ab, which protects corn from the European corn borer and a few other insects.

There is a corn variety that is very similar to MON810 corn, called its “isoline.” This is the variety of corn that was altered in the laboratory using transgenic techniques to express the one, added trait (expressing the genes that produce Cry1Ab toxins).

Rats were divided into two groups and were fed a diet containing either 30% of MON810 GE corn or 30% of the isoline, non-GE corn.[1]

Initial findings showed that the two types of corn were not identical nutritionally: the concentrations of proteins, carbohydrates, fat content, and other parameters differed between the two types of feed. Presumably, these differences resulted from the genetic modification, since both the GE corn and its isoline were grown side-by-side in the same type of soil and were subject to the same weather in order to eliminate other possible factors that might account for differences.

Analysis of the rats’ organs also revealed differences. After 45 days, a first group of rats was sacrificed and the authors found differences in the weight of their organs: male rats eating GE corn had enlarged spleens, and female rats, enlarged livers. A second group was sacrificed after another 45 days. In this group, the males on GE feed had enlarged spleens, livers, and kidneys, while the females had enlarged livers and spleens.

The researchers went on to analyze blood taken from the rats and examine their livers under the microscope. They found several differences between the groups. Under the microscope, the enlarged livers showed signs of damage. The blood tests were consistent with the visual evidence, revealing increased levels of liver enzymes, a clear sign of liver damage (as liver cells rupture, liver enzyme levels in the bloodstream rise).

Relevance to human health

GE corn cultivation has increased exponentially in the last 20 years.[2] The vast majority of GE-Bt corn has been fed to animals, converted to ethanol, or used to make corn oil or high fructose corn syrup. Scientists have done very little work to trace the ways in which GE corn proteins are entering the human food supply, but it is certain that some are via foods such as corn flakes and tortillas that are made from GE corn.

In 2014, a new brand of GE sweet corn that expresses two Bt toxins was approved. This is the first food on the US market that will expose humans to such a substantial amount of mostly intact Bt toxins.

Are the effects reported in the above study relevant to human health? If the answer is yes, then we would expect to be witnessing an increase in liver damage among humans, at least in populations exposed at higher levels to Bt toxins because of dietary preferences or occupational exposures (e.g., via corn grain dust).

Such damage is, in fact, occurring more frequently than during the pre-GE crop era (prior to 1996).

There are two liver diseases presently on the rise: non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). Both of these can progress to liver failure or cancer. The progression to disease becomes easily apparent when liver cells become damaged sufficiently to trigger a rise in liver enzymes.

Liver disease is related to lifestyle, especially the consumption of fast foods, most of which contain genetically engineered products. No one has connected this disease directly to corn consumption or to any of the Bt toxins in corn. However, NAFLD has doubled in adolescents, for example, over the last 20 years.[3] While the trend toward excess weight and obesity is no doubt a risk factor, scientists believe there must be other risk factors yet to be identified behind the recent increases in the frequency and severity of liver disease.

GE corn and the pesticides used in conjunction with today’s leading varieties may or may not be among the risk factors impacting liver health. A human feeding study would have to be undertaken to settle the issue. However, such a study poses enormous logistical difficulties, and there are several important GE corn traits that would need to be assessed one trait at a time as well as in combinations matching the traits in today’s important “stacked” varieties.

Without such studies, we cannot be assured that any GE corn is safe for human consumption. And so, the nation faces a conundrum – the science needed to resolve key public health questions arising from GE crop technology is proving, so far, too costly and difficult to carry out.


  1. Abdo EM, Barbary OM, Shaltout OE. 2014. Feeding Study with Bt Corn (MON810: Ajeeb YG) on Rats: Biochemical Analysis and Liver Histopathology. Food and Nutrition Sciences, 5, 185-195 
  2. USDA Economic Research Service. 2015. Adoption of Genetically Engineered Crops in the United States, 1996-2015: Recent Trends in GE Adoption 
  3. Welsh JA, Karpen S, Vos MB. 2013. Increasing prevalence of nonalcoholic fatty liver disease among United States adolescents, 1988-1994 to 2007-2010. J Pediatr. Mar;162(3):496-500 

Hasn’t the EPA found levels of Roundup® pesticide used on GE food to be safe?

Actually they have not. The agency has not carried out a comprehensive glyphosate dietary risk assessment for many years and lacks the data to do so today.

To conclude that a pesticide applied on food crops is safe, the EPA must

  • Set an allowable level of intake, called a chronic Reference Dose or a chronic Population Adjusted Dose;
  • Quantify dietary and other exposures; and
  • Compare cumulative exposure to the presumably safe, allowable level.

Testing for glyphosate residues in food is costly ($300 or more per sample) and must be done using methods that also detect glyphosate’s primary metabolite, AMPA. Although data are presently sparse, regulators project that AMPA is either just as toxic as glyphosate (e.g., the US EPA), or 1.5 times more toxic (e.g., European regulators and the United Nations’ Food and Agriculture Organization).[1]

Such an updated dietary risk assessment is definitely needed because it is clear that glyphosate and AMPA are present in an increasing array of foods, and at higher levels than when the EPA last assessed glyphosate dietary exposure in the early 1990s.[2]

There are three major reasons why dietary exposure has increased:

  1. There has been an increase in the rate and number of applications of glyphosate on soybean crops worldwide. Average residue levels have also risen in nearly all soybeans. These residues find their way into a wide variety of foods because soybeans comprise part of their ingredients and because the residues spread in the environment.
  2. Glyphosate and AMPA are increasingly present in drinking water and other beverages, leading to exposures that EPA counts as part of diet.
  3. Industry has sought, and regulators have approved, a long list of pre-harvest uses of glyphosate to burn down crops and thereby accelerate harvest operations. Such applications result in much higher residues in harvested crops. This is why Monsanto has recently petitioned the EPA and other regulators worldwide to dramatically raise allowable tolerance levels for glyphosate in a variety of grains and foods.[3]

There is also a pressing need for the EPA and other regulators to reassess glyphosate’s chronic Reference Dose, which is now set at a very high level.

Because of the need to update exposure levels and reassess allowable levels of exposure, the EPA has therefore no basis to judge that today’s levels of exposure are safe.



  1. Bøhn T, Cuhra M, Traavik T, Sanden M, Fagan J, Primicerio R. 2014.Compositional differences in soybeans on the market: Glyphosate accumulates in Roundup Ready GM soybeans. Food Chemistry 153:207–215 
  2. Grossman, E. 2015 What Do We Really Know About Roundup Weed Killer? National Geographic, 23 April. 
  3. Environmental Protection Agency. 2013. Pesticide Tolerances: Glyphosate. 1 May .!documentDetail;D=EPA-HQ-OPP-2012-0132-0009 

What are some advantages to labeling foods containing GE products?

  1. Advancing Science: Doctors and epidemiologists need to know when patients and other people have consumed GE foods in order to have a realistic chance to understand possible linkages between consumption of GE food and human health risks.
  2. Facilitating Trade: Most of the civilized world[1] requires that GE food be labeled, and so the US food industry must label GE food in order to export food to many countries.

What is the difference between a genetically engineered (GE) food and a food without genetically engineered ingredients?

GE seeds have had DNA from a different species introduced into their cells. This could be DNA from a different plant, an animal, or bacteria. Most types of GE organisms have more than one gene introduced so scientists can track whether the introduction was successful. For example, some contain a gene for resistance to some antibiotics. These genes turn on during the life of the plant and become the blueprint for new proteins made by the plant, proteins with functions previously unavailable to that type of plant.

There are also differences in the way GE foods are grown. For example, the function of the RoundupReady®, gene is to allow the farmer to spray this herbicide (containing the chemical glyphosate) on the crop to kill weeds without worrying about killing the crop. As Roundup®, becomes incorporated into the plant, the consumer will, in fact, be exposed to the herbicide when consuming these foods. When not using a RoundupReady® crop, the farmer has to use a different way to prevent weed infestations. Organic farmers use mulching or tilling to minimize pest damage. Non-organic farmers may use different herbicides.

In the US, 99% of GE crops in use (1) were developed for two reasons:

  1. To allow farmers to spray herbicides on their crops to kill weeds without killing the crops themselves, i.e., RoundupReady® seeds
  2. So the crop itself makes an insecticide called a Bt toxin

Plants grown from this type of genetically modified seed will continually produce the Bt toxin in the plant itself. Such a plant is actually registered as a pesticide.

A very small fraction (about 1%) of the GE foods on the market were developed for other reasons, such as resistance to a virus (papaya and squash), and resistance to browning when sliced (apples). Some foods not yet on the market include salmon (developed for a faster growth rate), and vitamin A rich rice (developed for areas of the world where vitamin A deficiency is common).


  1. USDA Economic Research Service: Adoption of Genetically Engineered Crops in the U.S: Recent Trends in GE Adoption