Pig feeding study not reassuring

February 2012

Amidst the dearth of animal feeding studies actually designed to assess the safety of GM food, a paper has at last been published which is like a breath of fresh air. The study is relevant to humans; it recognises and minimises confounding factors in the experimental materials; it examines specifically the organs which will be affected directly by toxic qualities in food; and it acknowledges its own limitations.

Pigs are a very good model for humans because their digestive system is very similar. During the first few weeks after weaning, piglets grow fast and so react quickly to dietary influences. A team of Irish scientists took advantage of these characteristics to carry out a study of the effects of consuming 'Bt' insecticidal maize, MON 810.

The investigation included careful sourcing of the GM maize and its genetically closest non-GM relative grown side-by-side. It checked for the presence of genetic, agri-chemical and fungal contaminants in the maize. Care was taken during preparation of the test- and control-diets to avoid contamination, and analysis of their physical and chemical composition was carried out. Special attention was paid to effects on the liver and kidneys (the major organs which deal with toxins in the body), and to blood parameters which indicate liver and kidney function. Special attention was paid also to the digestive tract (the organ exposed directly to food).

A number of interesting differences was found between the measured parameters:
  • The 'non-GM' control maize had, in fact, a very low-level presence of Bt genes, and a presence of Roundup-resistance genes which the scientists didn't have the resources to quantify.
  • The GM-fed piglets ate more, and gained more weight, but were not able to convert the feed to weight as efficiently as the controls (it was noted that increased weight gain after feeding various Bt-maize diets had been observed in other experiments but was thought to be due to lower fungal toxin levels in the GM plants which are assumed to suffer less insect damage).
  • The GM maize had a significantly different carbohydrate composition from its non-GM relative, and formed softer feed pellets.
  • The GM-fed piglets had heavier kidneys.
  • There were more 'goblet' cells in the gut lining of the GM-fed piglets.
Although the study was limited to male piglets, and lasted only 31 days (giving no time for adverse effects to show) there were several changes which could be indicative of wider or long-term problems.

In a recent review of long-term and multigenerational animal GM feeding studies, 15 out of the 24 citations were criticised because the researchers hadn't fed their control animals on plants which were genetically-identical except for the inserted DNA (Note that such test material isn't readily obtainable, so researchers often have to compromise). However, the criticism may be obsolete because, as the Irish study indicated, gene pollution is now so rife that truly non-GM material may no longer be available. Besides this, the GM plants exhibited important differences in kernel composition in addition to the presence of the Bt gene product (see below): in other words, the use of non-GM genetically equivalent plants doesn't actually provide an equivalent experimental control.

Piglets fed GM were over-eating. In other words, the GM-containing pellets were not being recognised by their bodies as being as nutritious and satisfying as the non-GM ones.

As the compositional analysis of the feed pellets showed, the production of the transgenic protein is certainly not the only difference between the GM and non-GM equivalent of this maize. Tests have shown that the artificial DNA construct in MON 810 has inserted into an existing gene: this has caused genomic scrambling leading to the production of novel DNA sequences which are expressing themselves in novel ways. Either the disruption from the DNA insertion, or influences arising from non-genetic regions of the artificial DNA, or the diversion of the plant's metabolism into Bt protein production, has significantly disturbed the carbohydrate metabolic pathways in the GM plants.

Differences in dietary carbohydrate composition have previously been linked to changes in the microbial flora in the pigs' digestive system. In a healthy pig gut, the microbes obtain the nitrogen they need from urea circulating in the blood. This has the effect of relieving the load on the kidneys which otherwise must excrete it. The authors considered the possibility that changes in the gut flora caused by the GM-related carbohydrate composition might be supporting microbes which use less urea. This would have the effect of increasing the work of the kidneys and could account for the bigger weight of these organs (the authors cited longer-term, unpublished data which further supported this possibility).

However, enlarged kidneys can also herald an immune response in progress. A paper just published on the acute effects of the same Bt-toxin as generated by MON 810 maize on human kidney cells in culture adds an ominous clue to the puzzle. At high concentrations, the Bt protein which has always been assumed to be insect-specific in its activity, inhibited cell respiration and disrupted the cell membrane (both markers of cell death in progress). The cell-culture exposure to Bt was limited to 24 hours, and only acute reactions to a high dose of toxin were detected: lower concentrations of Bt over a longer period could well prove damaging. There have been no long-term rodent feeding studies using GM maize.

Over-worked kidneys plus the need to deal with the stress from Bt and other environmental toxins could promote chronic disease, especially in compromised individuals such as those with diabetes.

homeostatic mechanism in the gut which is vital to health. The increase in numbers of goblet cells in the GM-fed piglets could be a symptom of an unfriendly presence in the gut, or altered microbial diversity to a less friendly state, or other on-going immunological reaction.

In what might, at first reading, appear an oddly out-of-place, but politically correct, comment from a team which had shown so much common-sense and very careful science up until that point, the paper reaches the unexpected conclusion that “... the present findings offer at least some assurance to consumers as to the safety of short-term exposure to GM food ...”. The authors end by pointing out that “long-term feeding studies are necessary”.


Why would these Irish scientists think anti-GM campaigners expect to drop dead after eating MON 810 maize for 31 days? The answer might lie in the bigger political scene. The closing statement was, of course, fed to the press, which duly trumpeted the headline that “Genetically Modified Food Safe, Animal Study Suggests” and reported that three pig studies (one short-term, one medium-term, and one generational) had been carried out. The press-release seems to have been jumping the gun a bit because only the first study has been published.

Given that most people would find the above results anything but reassuring, it's difficult to accept the integrity of the announcement regarding the other two studies which are not yet available for scrutiny. Sceptics might wonder if this pre-emptive press release was put out to distract attention from the realities of the actual overall findings?

Whatever the reason, the scientists were showing great common-sense in failing to reach a conclusion negative to GM: remember what has happened to other scientists (e.g. Pusztai, Chapela, Rosi-Marshall, Carrasco ...) when they pointed out their GM-unfriendly findings.

Make sure that when all these three studies are published, the actual results (not the politically-correct, biotech-friendly versions) are broadcast by the press.

Keep an eye on key GM-campaigning sites for further news of the pig-feeding studies, e.g. The Institute of Science in Society, GM Watch, GM Freeze, GM-free Scotland ...


  • Maria C. Walsh, et al., 2012, Effects of short-term feeding of Bt MON801 maize on growth performance, organ morphology and function in pigs, British Journal of Nutrition 107
  • Genetically Modified Food Safe, Animal Study Suggests, www.sciencedaily.com, January 2012
  • Questions over reporting of GM feed studies, GM Watch 26.01.12
  • Snell Chelsea, et al., 2011, Assessment of the health impact of G plants diets in long-term and multigenerational animal feeding trials: A literature review, Food and Chemical Toxicology
  • Yoshiyuki Goto & Hiroshi Kiyono, Epithelial cell microRNAs in gut immunity, Nature Immunology, 12:3, March 2011
  • Gilles-Eric Séralini, 2011, Genetically modified crops safety assessments: present limits and possible improvements, Environmental Sciences Europe, 23:10
  • R. Mesnage, et al., 2012, Cytotoxicity on human cells of Cry1Ab and Cry1Ac Bt insecticidal toxins alone or with a glyphosate-based herbicide, Journal of Applied Toxicology

1 comment:

  1. "Dearth of studies?" There have been hundreds of safety studies on GM food safety, a great many of them funded by the EU and they say there isn't a problem. This study on the other hand is an egregious example of junk science by someone with an agenda


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