Activists claim that without long-term studies, GMOs cannot be considered safe: What does science say?

Bob Demers / UA News

There have been more than a thousand studies, most of them by independent researchers, documenting the safety of GMOs. More than 270 independent global science oversight agencies–most recently the National Academies of Sciences, Engineering, and Medicine (NASEM)—have issued statements underscoring the safety of GM technology.

But still, more than a year after the 20-member NASEM panel’s comprehensive report confirmed that foods with genetically engineered ingredients are as safe as organic and other conventionally bred foods, dedicated anti-GMO activists remain unconvinced.

The opponents are familiar voices, fighting the battle against farming technology for more than a decade. Long-time critics Michael Hansen of Consumer Reports hyped the potential of ‘unknown’ and ‘unique’ dangers of allergens that could be created–the kind that might not be known unless regulators required long-term, multi-generational studies, he claimed. In fact, after more than 20 years of the consumption of billions of meals by humans and animals, there has not been one case of an unusual allergen identified in an approved food. Experts say there is no scientific or logical basis to believe that foods grown with one or two genes having been precisely tweaked and mapped would pose more allergenic problems that conventional and organic foods created with hundreds or thousands of genes of unknown origin, often created using radiation or chemicals (mutagenesis).

The UK Soil Association, a pro organic group that has opposed biotechnology and many technological advances in agricultural for decades, was more explicit in raising the specter that we have not studied GMO food effects for a long enough time, writing:


The report highlights there have been no long studies which have directly addressed the human health impact of GM food consumption.

In its web attack dossier on GMO foods, the London-based anti-technology group Earth Open Source devoted an entire section to what it said were the “myth” of GMO safety, repeating the claim that “Few long term studies have been carried out.”

[NOTE: Read Genetic Literacy Project Biotech Gallery profile of Earth Open Source here]

Claims of ‘No long term studies’ has been the fall-back cry of advocacy groups for years. It’s a meme repeated almost word for word throughout the anti-GMO online community, particularly by labeling groups and organic food companies attempting to stigmatize conventional foods.

“Because GMOs are still a new science, there have been no long-term studies to substantiate their exact effect on our health” claims the natural products company Aunt Millies. Label GMOs states, “Few long-term studies have been carried out”.

In the wake of the Academies report, it’s one of the few claims left that haven’t been directly addressed.


What are the facts?

Simply said, the claims of ‘no long term studies’ is inaccurate. Almost all science research is done on animals, and there is a long and growing history of dozens of long term studies on the potential impact of genetically modified ingredients.

A few years ago, the science website Skeptic Ink carried a summary listing dozens of long-term safety studies. The GENERA database, found at the independent Biology Fortified site, lists more than three-dozen examples of multi-year studies.  A review of 24 of these by Snell et. al found: “Results…do not suggest any health hazards and, in general, there were no statistically significant differences within parameters observed.” The authors concluded: “The studies reviewed present evidence to show that GM plants are nutritionally equivalent to their non-GM counterparts and can be safely used in food and feed.”

Here is a partial list of dozens of studies longer than 90 days (more here) on GMOs–none of which has shown serious safety issues:

  • Assessment of the health impact of GM plant diets in long-term and multigenerational animal feeding trials: A literature review: We examined 12 long-term studies (of more than 90 days, up to 2 years in duration) and 12 multigenerational studies (from 2 to 5 generations). … The studies reviewed present evidence to show that GM plants are nutritionally equivalent to their non-GM counterparts and can be safely used in food and feed.
  • A three generation study with genetically modified Bt corn in rats: Biochemical and histopathological investigation: This study was designed to evaluate the effects of transgenic corn on the rats that were fed through three generations with either GM corn or its conventional counterpart. Tissue samples of stomach, duodenum, liver and kidney were obtained for histopathological examinations. … No statistically significant differences were found in relative organ weights of rats within groups but there were some minimal histopathological changes in liver and kidney.
  • Effects of long-term feeding of genetically modified corn (event MON810) on the performance of lactating dairy cows: A long-term study over 25 months was conducted to evaluate the effects of genetically modified corn on performance of lactating dairy cows. Thirty-six dairy cows were assigned to two feeding groups and fed with diets based on whole-crop silage, kernels and whole-crop cobs from Bt-corn (Bt-MON810) or its isogenic not genetically modified counterpart (CON) as main components. … Milk yield (23.8 and 29.0 kg/cow per day in the first and the second lactation of the trial) was not affected by dietary treatment. There were no consistent effects of feeding MON810 or its isogenic CON on milk composition or body condition. Thus, the present long-term study demonstrated the compositional and nutritional equivalence of Bt-MON810 and its isogenic CON.
  • Organic and Genetically Modified Soybean Diets: Consequences in Growth and in Hematological Indicators of Aged Rats: There was an organic soy group (OG), a genetically modified soy group (GG), and a control group (CG). All animals received water and diet ad libitum for 455 days. At the end of this period, the weight of the GG group was the same as that of the OG, and both were higher than CG. Protein intake was similar for the OG and GG, which  were significantly lower (p<0.0005) than the CG. The growth rate (GR) of the rats, albumin levels, and total levels of serum protein were comparable for all groups.  Hematocrit (p<0.04) and hemoglobin (p<0.03) for the OG and GG were less than the CG. Although the OG and GG demonstrated reduced hematocrit and hemoglobin, both types of soy were utilized in a way similar to casein. This result suggests that the protein quality of soy is parallel to the standard protein casein in terms of growth promotion but not hematological indicators.
  • Histochemical and morpho-metrical study of mouse intestine epithelium after a long term diet containing genetically modified soybean: In this study, we investigated the duodenum and colon of mice fed on genetically modified (GM) soybean during their whole life span (1–24 months) by focusing our attention on the histological and ultrastructural characteristics of the epithelium, the histochemical pattern of goblet cell mucins, and the growth profile of the coliform population. Our results demonstrate that controls and GM-soybean fed mice are similarly affected by ageing. Moreover, the GM soybean-containing diet does not induce structural alterations in duodenal and colonic epithelium or in coliform population, even after a long term intake. On the other hand, the histochemical approach revealed significant diet-related changes in mucin amounts in the duodenum. In particular, the percentage of villous area occupied by acidic and sulpho-mucin granules decreased from controls to GM-fed animals, whereas neutral mucins did not change.

(more here)

Food safety studies are done on animals

The anti-GMO activists often add a twist to their criticism: Some concede long term animal studies but then add the caveat that there have been no long-term studies on humans. They are correct that there have not been human clinical trials on GMOs. This is not out of the ordinary. No existing food or ingredient, GMO or otherwise, has been the subject of extended multi-year human clinical trials. IT would be unethical. Humans are also very poor experimental subjects: we age and reproduce slowly, and our genetic diversity and predisposition to diseases like cancer and arthritis during aging would confound experimental results.

Related article:  Food Evolution director Scott Hamilton Kennedy: 'I wanted to reset the debate' over food and farming

Animal trials provide the best proxy for human experimentation. There is broad and global agreement in the science community that animal studies are the ethical way to assesses potential dangers to humans. Animal testing falls into two categories: controlled trials and monitoring experiments. Controlled studies are clinical trials in which animals are assigned to two groups used for comparison purposes. Other variables such as housing and exposure to other animals can be controlled. Monitoring trials look at livestock which have been fed GMO crops and assess the health of these animals, either in vivo or through data analysis. Where possible, reference will be made to a control group of animals fed a comparable non-GM diet.


Anti-GMO activists claim, anecdotally, that animals eating GMO grain and feed have been beset by problems. Anti-GMO crusader Jeffrey Smith, on his personal website, the Institute for Responsible Technology, lists more than a dozen cases in which he claims animals fed GMOs exhibited abnormal conditions, including cancer and early death. He also references his own self-published book, and anecdotal evidence that pigs fed GM feed turned sterile or had false pregnancies and sheep that grazed on BT cotton plants often died.

“Nearly every independent animal feeding safety study on GM foods shows adverse or unexplained effects,” he writes. “But we were not supposed to know about these problems…the biotech industry works overtime to try to hide them.”

The American Academy of Environmental Medicine — a quack alternative medicine group that rejects GMOs and believes that vaccines are dangerous — claims, “Several animal studies indicate serious health risks associated with GM food,” including infertility, immune problems, accelerated aging, faulty insulin regulation, and changes in major organs and the gastrointestinal system.

Is there any basis to these allegations? After all, globally, food-producing animals consume 70 percent to 90 percent of genetically engineered crop biomass, mostly corn and soybean. In the United States alone, animal agriculture produces over 9 billion food-producing animals annually, and more than 95 percent of these animals consume feed containing GE ingredients, according to the U.S. Department of Agriculture. The numbers are similar in large GMO producing countries with a large agricultural sector, such as Brazil and Argentina. Europe, which generally shuns GMO food in human markets, feeds most of its livestock GMO based feed.


Estimates of the numbers of meals consumed by feed animals since the introduction of GM crops 18 years ago would number well into the trillions. By common sense alone, if GE feed were causing unusual problems among livestock, farmers would have noticed. Dead and sick animals would literally litter farms around the world. Yet there are no anecdotal reports of such mass health problems.

Historic Van Eenennaam animal feeding story

But we don’t need to depend on anecdotes to address these concerns. A comprehensive monitoring study published in the Journal of Animal Science, by animal genomics expert Alison Van Eenennaam and assistant Amy Young at the University of California-Davis investigated the impact of GM feed on livestock. The study looked at data about animal health over a 29-year time period — both before and after the introduction of GM feed in 1996.

They conclude that data from 100 billion animals over 29 years ‘did not reveal unfavorable or perturbed trends in livestock health and productivity’. The study also concluded that there is no evidence of genetically modified material in milk or eggs from animals fed GM food: ‘Studies have been conducted with a variety of food-producing animals including sheep, goats, pigs, chickens, quail, cattle, water buffalo, rabbits and fish fed different GE crop varieties. The results have consistently revealed that the performance and health of GE-fed animals were comparable with those fed… non-GE lines and commercial varieties’.


The study received widespread media exposure spurred by an article by GLP’s Jon Entine in Forbes,  “The Debate About GMO Safety Is Over, Thanks to a New Trillion-Meal Study.” GM skeptics jumped on the Van Eenennaam study and the Entine report. GMWatch issued a searing rebuttal, “ Why Jon Entine’s ‘trillion meal study’ won’t save us from GMO dangers.”

Anti-GM campaigners questioned the validity of monitoring studies in the absence of controlled trials, stating that “Van Eenennaam and Young’s data do not represent a controlled study”. Critics also denounced the study on the basis of being “short-term in relation to the animal’s natural lifespan” and therefore “not able to reveal long-term ill health effects, which take time to show up”.

The criticisms don’t hold up under scrutiny. There are in fact hundreds of studies, many of them multigenerational and long term, into the safety of GM food for livestock. One controlled study published in the Archives of Animal Nutrition, across ten generations of quails, noted that feeding the animals 50 percent GMO corn “did not significantly influence health and performance of quails nor did it affect DNA-transfer and quality of meat and eggs of quails” compared to the control group.

When GMO corn was fed to cows in another controlled study, published in Journal of Animal Physiology and Animal Nutrition, over 25 months, “Milk yield was not affected by dietary treatment. There were no consistent effects… on milk composition or body condition… Long-term study demonstrated the compositional and nutritional equivalence (of GMO and non-GMO feed)”.


A vast new database of studies investigating GM feed has been recently published by the Information Platform for Animals Health and Feed, an independent organization funded by the European Commission. IPAFEED provides an even more comprehensive overview of the current state of scientific knowledge in this field. The open-access database summarizes the findings from over 3,000 papers, covering three main safety aspects of animals fed GM feed: controlled trials on the effect of the feed on animal health and productivity; assessing whether the transgenic DNA in crops ends up in animal tissues; and monitoring programs. In addition, many of the studies are long term, including more than 80 studies over two years in length.

The EC’s IPAFeed database definitively puts to rest any doubt over a claimed dearth of controlled trials: 3,000 are presented. The evidence is overwhelming: no evidence has been found for adverse health effects or transgenic contamination of dairy products. For example, in 38 studies of cows fed crops genetically modified to be insect- or herbicide- resistant, no detectable transgenic DNA was found in milk.

Monitoring data spanning twenty years and relating to billions of animals worldwide fed on GM crops have not found any evidence of health hazards as a result of GM feed. A slew of controlled studies, many of them long-term, into the effects of GM feed on livestock point to the same conclusion: there is no evidence to suggest that GM feed–or the foods that humans eat–is unsafe.

Jon Entine is executive director of the Genetic Literacy Project. Follow @JonEntine on Twitter

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