Irritable bowel syndrome link to GM food

May 2013

'MON810' insecticidal maize is the only major GM feed crop permitted for cultivation in Europe.

However, eight European countries have banned it, and recently, Italy has moved this a stage further and asked the European Commission to withdraw its approval for the crop.

The scientific and anecdotal evidence of problems in livestock fed MON810 and other 'Bt' crops is mounting but fragmented and inconsistent. Over a dozen feeding studies measuring various parameters in various animals given various Bt-based feeds have been published. All have found physiological changes in the animals. Some of the results support each other, others do not, and all are short-term. More than anything else, they highlight the gaps: there's an absence of long-term experiments; there's a lack of in-depth physiological studies, especially of intestinal and immune responses. Most of all, it's clear that no one knows what to look for: there's an urgent need to identify key biomarkers for Bt-maize-linked symptoms

The latest feeding study to be published has shed at least some new light on the biomarker question. It involved a very detailed look at salmon fed GM maize for periods of 1 and 3 months.

Farmed salmon are commonly feed maize 'gluten meal' which is a mildly treated protein extract of the kernels. Any transgenic or unexpected protein by-products in such feed should be concentrated and largely intact. Previous studies suggest that the MON810 Bt protein itself would survive this processing partially intact: it would retain its pore-forming ability which kills cells by damaging their outer membrane, but it's ability to latch on to target cells would be impaired.

Besides comparing MON 810 maize with its closest relative (near isogenic counterpart), the scientists tested what happened when the fish were sensitised by the inclusion of soya meal which induces symptoms similar to Irritable Bowel Syndrome (IBS) in humans.

They looked at a wide range of physiological responses including growth, digestive function, basic health parameters (blood cells and chemistry, organs), immune reactions and stress.

No differences were found in the growth and blood parameters (COMMENT Note that these are the main health biomarkers routinely used in feeding 'safety' trials). However, this more detailed investigation found changes in nutrient metabolism, such as reduced lipid stores and impaired mineral digestion, suggesting the the fish were unable to use the GM feed as efficiently as conventional maize.

Inclusion of the soya sensitiser, induced localised intestinal immune responses and potentiated inflammation. (COMMENT Note that Bt toxins which are less processed and so retain all their toxin-promoting potential could be much more harmful)

The authors noted that their findings differed from those in a 2007 paper on the same animal fed the same GM maize event: the previous study found reduced growth and increased organ weight, but no change in nutrient metabolism. This suggests these particular parameters, which are the ones routinely relied on to assess feeding quality and have been extrapolated into 'safety' studies, are too insensitive to use for the latter. The development of gut-cell proliferation tests appears to offer a more reliable biomarker for Bt effects.


Since maintenance of the gut requires as much as 20-25% of nutrient energy requirements, adverse cell reactions could certainly be debilitating. Add to this that 5-11% of the population of most countries suffer from IBS, and many more cases probably go unreported: such people could well be hyper-sensitive to the effects of Bt maize.

None of the Bt feeding studies have given MON 810 a clean bill of health, but few are pointing in exactly the same direction. Something's wrong, but what?

The authors of the latest publication seem to be the first one to raise the issue of “other antigens” which might be present in GM feed besides the Bt protein and could produce side-effects.

This is a key point, especially in light of the variations in physiological changes found in different experiments. Such “other antigens” could be emerging in the Bt-plant physiology in response to varying environmental influences or agronomic regimes.

It's worth remembering Arpad Pusztai in Aberdeen, who was commissioned to develop safety testing for GM foods back in the 1990s. Dr Pusztai also homed in on adverse reactions in the intestinal cells: his success in finding them triggered the first of many orchestrated defamatory attacks on scientists who dared to publish GM-unfriendly results.

Perhaps its time we insisted that regulators revisit the type of tests of harm Dr. Pusztai was working on, and develop the sort of biomarkers highlighted by this Bt-feeding study.

  • Jinni Gu et al., 2013, Effects of oral Bt-maize (MON810) exposure on growth and health parameters in normal and sensitised Atlantic salmon, Salmo salar L., British Journal of Nutrition, 109
  • R. Spiller et al., 2007, Guidelines on the irritable bowel syndrome: mechanisms and practical management, Gut 56
  • IBS - Epidemiology,, April 2013
  • Italy asks EU to halt GM maize cultivation, 4.04.13

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