December 2013 Issue

Can GMOs Harm Digestive Health? — A Controversial Animal Study Suggests GMOs May Cause Stomach Inflammation

By David Yeager

Today’s Dietitian

Vol. 15 No. 12 P. 12

Few questions invoke as much heated debate as whether genetically modified (GM) foods are safe. On one side, the biotech industry and its supporters see GM foods as a way to increase crop yields and improve plants’ resistance to disease and pesticides, potentially opening the door to feeding millions of starving people and keeping rising food prices in check. On the other side, those who believe that GM products require more oversight argue that foods containing genetically modified organisms (GMOs) should be labeled, if not banned outright, because of potential harm to humans and ecosystems. It’s been a burning issue for more than two decades, and a study published in June in the Journal of Organic Systems is the latest log on the fire.

The peer-reviewed study measured the effects of a GM vs. non-GM corn and soy diet in two groups of pigs, including looking at the effects in regards to stomach inflammation. Pigs were used as test subjects because of the similarities between their digestive systems and those of humans. Two groups of pigs, containing equal numbers of males and females, were fed one of the two diets from weaning until 22.7 weeks of age, the typical life span of a commercial pig from weaning to slaughter. The pigs’ living conditions were identical to those of commercial pigs in the United States, and the particle size of the feed was standardized. At the study’s conclusion, two veterinarians performed necropsies. To avoid observational bias, neither veterinarian knew which pigs had been fed GM vs. non-GM feed.

The study found that GM-fed pigs had significantly higher rates of severe stomach inflammation than non–GM-fed pigs. In addition, the uterine weights of GM-fed females were 25% higher than non–GM-fed females. (Male sexual characteristics couldn’t be measured because male pigs that are grown for food are neutered shortly after birth.) There were no differences in weight gain or routine blood biochemistry between the two groups.

Two Sides to One Study

Because the study was conducted as a blinded randomized trial in commercial piggery conditions, its conclusions potentially have far-reaching implications. Not surprisingly, critics were quick to say there were flaws in the study’s design, methodology, and conclusions. There also have been claims that lead author Judy A. Carman, PhD, and her coauthors are biased against GM foods. For her part, Carman says she’s not anti-GM, just pro-safety testing, while pointing out that most of her critics have connections to the biotech industry.

Carman, who’s an adjunct associate professor at Flinders University in Adelaide, Australia, has a doctorate in medicine, specializing in nutritional biochemistry and metabolic regulation, and a master’s degree in public health, specializing in epidemiology and biostatistics. She says some of the staunchest criticism regarding the new study has come from people who aren’t trained in this kind of research, and she has posted rebuttals to many of these critics on her website. Perhaps the criticism that carries the most weight, though, is that of Food Standards Australia New Zealand (FSANZ), the food regulatory body for both countries.

Some of the key points of FSANZ’s response to Carman’s study were that the organization believed the study authors should have used histological examination with a microscope to determine inflammation levels rather than relying on visual measurement. The organization questioned the statistical approach to analyzing the inflammation data, and it believed the study researchers didn’t account for inconsistencies in the female pigs’ reproductive cycles.

Carman says she was surprised by the FSANZ response. “There were a number of things that FSANZ got very much wrong by saying that we did certain things that we did not do, even though it’s clearly written in the paper that we did not do those things. They’re also saying that we didn’t do some things that we did do,” she says. “They’ve made basic factual errors. The kindest thing I could say would be that they’ve not read the paper competently.”

Although histological analysis wasn’t used, Carman says the veterinarians’ observations are scientifically valid. She also says that most studies that have found no stomach inflammation in GM-fed animals have relied on visual observation, too, rather than histological analysis. In addition, she says FSANZ’s claim that certain mycotoxins weren’t measured, which could have influenced the results, is untrue.

FSANZ noted in its response that there were no signs of inflammation in the biochemical markers that were tested. Carman says standard biochemical measurements are inadequate to detect inflammation, although additional testing for biochemicals such as C-reactive protein can detect inflammation. FSANZ doesn’t share this view and cited that standard biochemical markers, such as white blood cell count, fibrinogen, total proteins, and albumin-to-globulin ratio, are sufficient markers of inflammation.

FSANZ and others also have questioned why, although the instances of severe inflammation in GM-fed pigs were statistically significant, there were more pigs with mild and moderate inflammation in the non-GM-fed group. Carman says the particle size of the feed, which was the same size as what’s commonly used in commercial feed has been shown to produce an underlying level of inflammation in pigs, regardless of whether or not they’re fed GM or non-GM feed. Although mild and moderate inflammation were present in greater numbers in the non-GM fed group, the differences between GM-fed and non-GM-fed pigs with mild or moderate inflammation weren’t statistically significant. She says FSANZ’s comment represents a basic error in interpreting statistics.

“It’s a process of how statistics works. You’ve got a certain number of pigs in the GM-fed group and a certain number of pigs in the non–GM-fed group, and what we found here was that eating the GM feed was taking animals from that low level of inflammation and boosting them up to that severe level. Those pigs have got to come from somewhere, so they’re coming from the mild and moderate range and being booted up to the severe range,” Carman says. “You wouldn’t expect to have more pigs from the GM-fed group in the mild and the moderate and the severe groups because you’d run out of pigs.”

As for the claim that the female reproductive cycles weren’t sufficiently accounted for, Carman says the females in both groups were at the same stage of sexual maturity, and the same number of pigs would have been in the same stage of their cycle in both the GM and non-GM groups. Aside from the errors she identified, Carman says it’s troubling that FSANZ didn’t cite any scientific studies to support its position. She’s currently preparing a rebuttal to address FSANZ’s concerns.

Dietary Considerations

So do GM grains present a risk for humans? It depends. The range of opinions varies widely, but this new study raises some interesting questions.

“There’s a distinction between whether something is a hazard, capable of causing adverse effects in mammals, and whether it poses a risk,” says Carl F. Cranor, PhD, a distinguished professor of philosophy and faculty member of the Environmental Toxicology Graduate Program at the University of California, Riverside. “Something can be a hazard, capable at some level of exposure of causing adverse effects, but not necessarily be a risk given a normal range of exposures.”

Cranor, who specializes in issues related to risks and science and the law, particularly as they relate to the concepts of acceptable risk, protection of susceptible populations, and societal approaches to the regulation of new technologies, says the study suggests that GM feed, at the dose it was given, had harmful effects on the pigs. How that translates to human populations remains to be seen. If there are any measurable effects in humans, Cranor says it also will be important to determine whether people who are already predisposed to gastrointestinal conditions have a more sensitive response to GM foods.

Determining whether GM foods pose significant risks for humans may be difficult. No institutional review board would approve a human study where one-half of the participants ate a strict diet of GM corn and soy. It’s also possible that the varied nature of human diets mitigates any potential consequences of eating GM foods.

In any case, not everyone is convinced that GM foods cause gastrointestinal harm to humans or animals. Joy Dubost, PhD, RD, CSSD, a food scientist and a spokesperson for the Academy of Nutrition and Dietetics, is skeptical of the study’s findings. She believes the methodology and statistics are flawed. She also says that nearly 80% of processed foods contain GM products, and there has been no spike in health problems associated with GM corn or soy coming into the marketplace. Dubost says the majority of studies have shown no link between GM products and adverse health effects, and numerous government organizations have deemed GM foods safe.

“According to the FDA and a number of US regulatory agencies that study and monitor food safety, genetically modified foods and ingredients are safe and pose no health risks,” she says. “Groups like the World Health Organization as well as the National Academy of Sciences and the American Medical Association have concluded that foods and beverages that contain GM ingredients are no different than foods without them. We shouldn’t discount the hundreds of other studies that have been published to indicate that GM foods are safe.”

Others, however, see a need for more studies like Carman’s. “I think it’s a really important study, and I know it’s received a lot of criticism, but I think it highlights the fact that we just don’t know enough about the long-term health effects of eating genetically modified food,” says Carole Bartolotto, MA, RD, a dietitian and exercise physiologist practicing in the Los Angeles area.

Bartolotto believes that GM foods should be labeled, and she notes that more than 60 countries, including China and Russia, require some form of GM labeling. Although there are no GM labeling requirements in the United States, she says there are a few ways to avoid GM foods if desired. One is to choose organic foods, especially when buying processed foods or fruits and vegetables that currently have GM varieties approved for the US market, including corn, soy, canola, cotton seed, sugar beets, Hawaiian papaya, zucchini, and crookneck squash. That may not be an option for some people, though.

Consumers also can look for the Non-GMO Project Verified seal, which is an independent, voluntary labeling program. Bartolotto says some retailers sell brands that are GMO free, such as Trader Joe’s brand or Whole Foods Market’s 365 Daily Value brand. She adds that extra-virgin olive and safflower oils, which aren’t made with GMOs, can be substituted for soy, corn, or canola oils, which are more likely to have GMOs.

Because this debate likely will continue for years to come, it’s difficult to make concrete dietary recommendations relating to GM foods. Lona Sandon, MEd, RD, LD, an assistant professor in the clinical nutrition department at the University of Texas Southwestern Medical Center at Dallas, says the question of how much of a GM food would be required to produce a response is significant and not easily answered. She recommends that people stick to a diet consisting mainly of whole foods, with an emphasis on fruits and vegetables, which is what most dietitians recommend to maintain optimum health.

As for Carman’s study, Sandon says it’s thought provoking, but she’s waiting to see more research before she draws any conclusions.

“Certainly, it’s intriguing and poses further questions about things that we might need to look at in future studies,” she says, “but we can’t suddenly make sweeping changes on food or health policy based on a single study.”

— David Yeager is a freelance writer and editor based in Royersford, Pennsylvania.