GM Corn Causes Tumors in Rats?
You may have heard about a recent French study into the health impacts of genetically modified (GM) corn published this week in the Journal Food and Chemical Toxicology. French researchers claim that rats fed a diet of GM corn (or exposed to the popular weed killer Roundup) are more likely to develop mammary tumors, organ damage and early death compared to rats fed a non-GM diet.
Though the study has been widely condemned by international scientists, we asked several Best Food Facts experts to review the study and share their thoughts.
Bruce Chassy, PhD
Professor of Food Microbiology and Nutritional Sciences; Executive Associate Director of the Biotechnology Center; Assistant Dean for Science Communications in the College of Agricultural, Consumer and Environmental Sciences, University of Illinois - Urbana/Champaign
Cecelia Chi-Ham, PhD
Director Science and Technology, PIPRA, University of California-Davis
Denneal Jamison-McClung, PhD
Associate Director - Biotechnology Program, Lecturer in Plant Biology in the College of Biological Sciences, University of California-Davis
Sally Mackenzie, PhD
Ralph and Alice Raikes Professor in the Department of Agronomy and Horticulture in the School of Biological Sciences, University of Nebraska-Lincoln
Wayne Parrott, PhD
Professor in the Department of Crop and Soil Sciences College of Agricultural & Environmental Sciences University of Georgia, University of Georgia
Our experts note several reasons to be skeptical about the validity and conclusions of the study.
Rat species and age
According to our experts, the species of rat used in the study are typically used in cancer studies specifically because they are prone to tumors regardless of what they eat. And the older these rats are, the more likely they are to develop tumors.
Dr. Wayne Parrot: “The study used a type of rat that is bred to get tumors. The rate of tumor formation found in the study is exactly the rate historically reported for this type of rat. Thus the study cannot say the diet caused it."
Bruce Chassy: “I believe it fair to say that the study will be found to totally without scientific merit. Old rats of this strain get tumors and the incidence of tumors reported over many studies and years is the same as that reported in the paper at hand. There is simply nothing new here, and nothing that implicates GM crops or glyphosate in toxicity.”
Sally McKenzie: “There has been no clear effort to control for the mouse line's inherent genomic instability (populations sizes are far too limited to do this properly), or to consider any alternative explanations to [the] results. [The researcher] similarly neglects to address the fact that no one else has observed such phenomena in the very large number of animal feeding studies done by other groups."
Limited sample size and faulty statistical analysis
Experts also note that the study design and analysis was complicated and did not adhere to international standards for studies of this type. They also raise concerns about the conclusions drawn by the study authors because of the small size of the control group—those rats on a non-GM diet.
Dr. Wayne Parrot notes, “There were 90 rats fed GM or herbicide diets, and only ten rats fed a standard diet. Therefore, odds are that one of the 90 rats would die first. Thus the earlier death of the feeding group is related to number of animals, not diet.”
Cecilia Chi-Ham also says, “It appears to be a rat line that will get over 50 percent tumors by two years of age no matter what you do. One control of 10 animals (of each, male and female) was compared to a number of treatments each with 10 animals each. So in the end, you have 180 animals receiving treatments and only 20 controls. So the likelihood of some getting some treatment differences seem pretty large, even if there is no effect."
According to Dr. Danneal Jamison-McClung, “The study design and analysis is not very good.”
You can find more from BFF experts on the safety of GM crops here: http://www.bestfoodfacts.org/food-for-thought/116