Genetically modified foods cause cancer

Genetically modified foods cause cancer
	FALSE
	"Eating genetically modified (GM) foods, such as GM maize, causes cancer and other serious diseases, as shown by studies in which rats fed GM corn developed large tumors."
Domain	Health & Medicine
Tactic	Statistical & Evidentiary Distortion; Pseudoscience / Junk Science;
Era	Current
First seen	2012
Origin	Study by Gilles-Éric Séralini and colleagues published in Food and Chemical Toxicology, September 2012, and accompanying media campaign
Last reviewed	2026-10-26
	Further reading: books on Health & Medicine

The claim that genetically modified foods cause cancer gained worldwide attention in September 2012, when a French research team led by Gilles-Éric Séralini published a study showing photographs of rats with large tumors after being fed genetically modified maize. The study was criticized by scientists and food-safety agencies for basic flaws in its design and analysis, and the journal retracted it in 2013. Large reviews and long-term studies have found no evidence that approved GM foods are more harmful to health than their conventional counterparts. The claim nonetheless influenced public opinion and policy in several countries.

The broader debate over genetically modified crops includes legitimate questions about corporate control of seeds, pesticide use and environmental effects. Those questions are separate from the claim that GM foods cause cancer, which the evidence does not support.

The claim

In its general form, the claim holds that eating GM foods causes cancer, organ damage and other diseases. The 2012 study became the most widely cited evidence for it.

Origin

On 19 September 2012, Food and Chemical Toxicology published a study by Séralini, a molecular biologist at the University of Caen, and colleagues. They fed rats NK603, a genetically modified maize engineered to tolerate the herbicide glyphosate (sold as Roundup), with or without Roundup, or gave them Roundup in their water, over two years. They reported that treated rats developed more tumors and died earlier than control rats, and published photographs of rats with grotesque tumors.

The study's release was unusual. Journalists were given access only if they signed confidentiality agreements that prevented them from consulting outside experts before publication, so the first wave of coverage carried no independent assessment. The release was coordinated with a book and a documentary film.

How it spread

The photographs spread worldwide within hours. News outlets ran them prominently, and campaign groups opposed to GM crops promoted them. Russia temporarily suspended imports of the GM maize, and Kenya banned imports of GM foods in late 2012, a ban that remained until 2022. The study was cited in debates over GM labeling and regulation in several countries.

How it was challenged

Scientists and regulatory agencies quickly identified serious problems:

Rat strain. The study used Sprague-Dawley rats, a strain that spontaneously develops tumors at high rates as it ages, especially over a two-year period. Tumors would be expected in many rats regardless of diet.
Small groups. Each group contained only ten rats of each sex, far too few to distinguish real effects from chance in a strain with high background tumor rates. Guidelines for cancer studies recommend at least 50 per group.
No dose-response. Effects did not increase consistently with dose; in some groups, rats fed more GM maize did better.
Statistics and presentation. The study did not report the tumor data with appropriate statistical analysis, and the photographs showed only treated rats, not tumor-bearing control rats.
Animal welfare. Rats were allowed to develop very large tumors, raising ethical concerns.

The European Food Safety Authority and food-safety agencies in Germany, France, Australia and New Zealand, Canada and elsewhere concluded that the study did not support its conclusions. In November 2013, Food and Chemical Toxicology retracted the paper. The editor said there was no evidence of fraud or intentional misrepresentation, but that the results were inconclusive and did not reach the threshold for publication. Séralini and colleagues republished the study in 2014 in another journal, Environmental Sciences Europe, without new peer review of the data, and continued to defend it.

What the evidence shows

Major scientific bodies have concluded that approved GM foods are as safe to eat as conventional foods. A comprehensive 2016 report by the US National Academies of Sciences, Engineering, and Medicine found no substantiated evidence that GM foods posed greater risks to human health than conventional crops, and no evidence of increased cancer rates linked to their introduction. European Union-funded long-term studies, including the GRACE and G-TwYST projects, which tested the same NK603 maize in rats for up to two years, found no adverse effects. The World Health Organization has stated that GM foods currently available have passed safety assessments and are not likely to present risks to human health.

Why it persisted

Vivid images. Photographs of tumorous rats were far more memorable than any statistical critique.
Controlled coverage. The confidentiality agreements ensured initial reports carried no independent scrutiny.
Broader distrust. Concerns about large agricultural corporations, pesticide use and the industrialization of food made many people receptive to evidence of harm.
The retraction gap. Retractions rarely receive the attention that original claims do.

Lessons for readers

Ask how many subjects a study used and whether that is enough to separate real effects from chance.
Look for a dose-response relationship. If more exposure does not mean more harm, be skeptical of the claimed effect.
Be wary when researchers prevent journalists from seeking independent comment.
Legitimate concerns about an industry do not make every health claim about its products true.

Sources

Gilles-Éric Séralini et al., "Long term toxicity of a Roundup herbicide and a Roundup-tolerant genetically modified maize," Food and Chemical Toxicology 50 (2012). Retracted 2013.
European Food Safety Authority, "Final review of the Séralini et al. (2012) publication," EFSA Journal (2012).
National Academies of Sciences, Engineering, and Medicine, Genetically Engineered Crops: Experiences and Prospects (2016).
Pablo Steinberg et al., "Lack of adverse effects in subchronic and chronic toxicity/carcinogenicity studies on the glyphosate-resistant genetically modified maize NK603 in Wistar Han RCC rats," Archives of Toxicology 93 (2019).
World Health Organization, "Food, genetically modified," questions and answers.