Truth: GM feed affects the health of animals and may affect the humans who eat their products

Myth at a glance

It has often been claimed that GM DNA and proteins in GM animal feed are broken down in the animals’ digestive tracts and are not detectable in the final food product. However, GM DNA present in animal feed has been detected in the milk and meat that people eat.

GM feed has been found to negatively affect the health of animals that eat it.

Other research shows that small molecules called microRNAs in any plants that are eaten, including GM plants, could have a direct physiological effect on human and animal consumers.

For all these reasons, meat, eggs, and dairy products from GM-fed animals should be labelled.

Most GM crops go into animal feed. In countries where GM foods have to be labelled, meat, eggs, and dairy products from GM-fed animals are exempt from labelling.

Is the absence of labelling justified? Historically, regulators and some sectors of the food industry have claimed that GM molecules – DNA and proteins – are broken down in the animals’ digestive tracts and are not detectable in the final food product.1,2 For example, in 2007 the European Food Safety Authority (EFSA) claimed: “After ingestion, a rapid degradation into short DNA or peptide fragments is observed in the gastrointestinal tract of animals and humans. To date, a large number of experimental studies with livestock have shown that recombinant DNA fragments or proteins derived from GM plants have not been detected in tissues, fluids or edible products of farm animals like broilers, cattle, pigs or quails.”2

However, such claims have been shown to be false by the following study findings, some of which were published before EFSA issued its statement:

  • GM DNA present in animal feed was detected in milk sold on the Italian market, though the authors of the study said it was unclear whether the source of the GM DNA was ingestion by the animal or external contamination.3
  • GM DNA in feed was taken up by the animals’ organs and detected in the meat and fish that people eat.4,5,6,7
  • Insecticidal Bt toxin proteins were found circulating in the blood of pregnant and non-pregnant women and the blood supply to foetuses.8,9 It is not known if the Bt toxin proteins originated from GM Bt crops or from Bt sprays used in chemically-based and organic agriculture. Similarly, the exposure route (dietary or inhalation) is not known. However, the study shows that the assumption that Bt toxin proteins are broken down in the mammalian digestive tract and are unable to reach the blood and organs is false.
  • GM feed was found to affect the health of animals that eat it. GM DNA from soy was detected in the blood, organs, and milk of goats. An enzyme, lactic dehydrogenase, was found at significantly raised levels in the heart, muscle, and kidneys of young goats fed GM soy.10 This enzyme leaks from damaged cells during immune reactions or injury, so high levels may indicate such problems. It is not possible to tell from this study whether this effect was due to the presence of GM DNA in the feed or some other aspect of the GM crop, such as changes in a protein in the crop or residues of the pesticides sprayed on the growing crop.

After it became widely known that the evidence does not support claims that GM DNA is not detectable in the final product, in 2012 the UK Food Standards Agency (FSA) conceded: “It is… possible that DNA fragments derived from GM plant materials may occasionally be detected in animal tissues, in the same way that DNA fragments derived from non-GM plant materials can be detected in these same tissues.”11

However, the FSA’s statement appears to be a gross understatement in light of a 2013 study in humans which showed that DNA fragments large enough to carry complete genes can avoid degradation in the digestive tract and pass from food into the blood.12 This study was not on GM foods but its findings would apply equally to GM and non-GM foods.

The stretches of plant DNA were complete enough to enable the researchers to identify the plants that the human subjects ate, such as soy, maize, and oilseed rape. The researchers even found that one of the blood serum samples had a higher concentration of plant DNA than human DNA.12

The highest concentrations of plant DNA were found in people with inflammatory diseases such as inflammatory bowel disease and Kawasaki disease, an autoimmune disease in which the blood vessels become inflamed.12

It should be noted that the presence of intact genes in the circulation does not imply that they are functioning (expressing). Several steps would need to happen for this to take place, namely:

  1. Uptake by cells
  2. Integration into the host cell DNA
  3. In the case of a plant-derived gene, integration in a location and orientation that would allow a host promoter to switch on the gene and make it express (plant promoters are highly inefficient in animals and humans).

It can be concluded that the chances of expression are low. The most plausible adverse health consequence would result from intact genes being taken up by bacteria and expressed. If there are intact genes in the blood of the consumer, this implies that there are intact genes in the gut, which could then be taken up by bacteria and expressed. This needs to be investigated experimentally.

Nevertheless, it has been shown that another type of DNA molecule ingested in food can affect animals that eat them. MicroRNAs (miRNAs, a type of double-stranded RNA molecule that is involved in the regulation of many genes) of plants were found in the blood of humans and animals that had eaten them. In experiments on mice, microRNAs from rice plants that the mice had eaten were found to be biologically active, affecting gene expression and the functioning of important processes in the body.13

While this study was not carried out with GM plants, it showed that any plants that are eaten, including GM plants, could have a direct physiological effect on human and animal consumers.13 The study suggested that the saying, “You are what you eat”, may have some scientific credibility.

Many GM crops are being tested and are in the pipeline for regulatory approval that are engineered to express novel miRNA sequences, either to impose control on host plant genes or to act as insecticides. Regulators have not assessed these products adequately.14

Does any of this matter? The UK Food Standards Agency would conclude that it does not, since “food from animals fed on authorized GM crops is considered to be as safe as food from animals fed on non-GM crops.”11

However, this claim has been shown to be false by the animal feeding studies discussed earlier in this chapter. The studies show that a diet containing GM crops can damage the health of animals. Therefore there could also be risks to the humans that eat products derived from unhealthy GM-fed animals.


The argument that meat, eggs, and dairy products from GM-fed animals do not need to carry a GM label cannot be scientifically justified, since in some cases those products may contain GM DNA and could even be materially changed as a result of the animals’ consumption of GMOs. In addition, some GM crops have been shown to have toxic effects on laboratory and farm animals, so consumers eating meat and dairy products from animals raised on GM crops may be eating sick animals.


  1. Mann A. Stores retreat on GM feed. The Scottish Farmer. Published April 18, 2013.
  2. European Food Safety Authority (EFSA). EFSA statement on the fate of recombinant DNA or proteins in meat, milk and eggs from animals fed with GM feed. 2007. Available at:
  3. Agodi A, Barchitta M, Grillo A, Sciacca S. Detection of genetically modified DNA sequences in milk from the Italian market. Int J Hyg Env Health. 2006;209:81–8. doi:10.1016/j.ijheh.2005.08.005.
  4. Mazza R, Soave M, Morlacchini M, Piva G, Marocco A. Assessing the transfer of genetically modified DNA from feed to animal tissues. Transgenic Res. 2005;14:775–84. doi:10.1007/s11248-005-0009-5.
  5. Sharma R, Damgaard D, Alexander TW, et al. Detection of transgenic and endogenous plant DNA in digesta and tissues of sheep and pigs fed Roundup Ready canola meal. J Agric Food Chem. 2006;54:1699–1709. doi:10.1021/jf052459o.
  6. Chainark P, Satoh S, Hirono I, Aoki T, Endo M. Availability of genetically modified feed ingredient: investigations of ingested foreign DNA in rainbow trout Oncorhynchus mykiss. Fish Sci. 2008;74:380–390.
  7. Ran T, Mei L, Lei W, Aihua L, Ru H, Jie S. Detection of transgenic DNA in tilapias (Oreochromis niloticus, GIFT strain) fed genetically modified soybeans (Roundup Ready). Aquac Res. 2009;40:1350–1357.
  8. Aris A, Leblanc S. Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada. Reprod Toxicol. 2011;31.
  9. Aris A. Response to comments from Monsanto scientists on our study showing detection of glyphosate and Cry1Ab in blood of women with and without pregnancy. Reprod Toxicol. 2012;33:122-123.
  10. Tudisco R, Mastellone V, Cutrignelli MI, et al. Fate of transgenic DNA and evaluation of metabolic effects in goats fed genetically modified soybean and in their offsprings. Animal. 2010;4:1662–1671. doi:10.1017/S1751731110000728.
  11. Food Standards Agency (UK). GM material in animal feed. 2013. Available at:
  12. Spisak S, Solymosi N, Ittzes P, et al. Complete genes may pass from food to human blood. PLOS ONE. 2013;8(7):e69805.
  13. Zhang L, Hou D, Chen X, et al. Exogenous plant MIR168a specifically targets mammalian LDLRAP1: Evidence of cross-kingdom regulation by microRNA. Cell Res. 2012;22(1):107-126. doi:10.1038/cr.2011.158.
  14. Heinemann J, Agapito-Tenfen SZ, Carman J. A comparative evaluation of the regulation of GM crops or products containing dsRNA and suggested improvements to risk assessments. Environ Int. 2013;55:43–55.