3-Food: UK study underestimated GE DNA content in human gut
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TITLE: GM DNA in Human Gut Underestimated
SOURCE: The Institute of Science in Society, UK, by Mae-Wan Ho
DATE: July 21, 2002
------------------ archive: http://www.gene.ch/genet.html ------------------
GM DNA in Human Gut Underestimated
UK's Food Standards Agency dismissed its new research findings that GM DNA
in food has transferred to bacteria in the human gut. Dr. Mae-Wan Ho
reveals how the experiment was designed to bias against positive findings,
so the actual transfer of GM DNA could be much more extensive. There should
now be a comprehensive ban on all GM crops, she says.
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That GM DNA should transfer to bacteria in the human gut is not at all
unexpected. We already know that DNA persists in the gut, and that bacteria
can readily take up foreign DNA. Why did our regulators wait so long to do
the experiment? And an experiment that's designed against making positive
The research in question is the final part of the Food Standards Agency
(FSA) project on evaluating the risks of GMOs in human foods, commissioned
by the former Ministry of Agriculture, Fisheries and Food (MAFF).
A single meal containing GM soya was fed to human subjects. It consisted of
commercial soya meal - 150g El Corte Ingles, batch number and GM content
unspecified - mixed in the burgers and soya protein supplement - 100g
Holland and Barrett, batch number and GM content again unspecified - mixed
in 'milk' shakes. No data were presented on how much DNA was present in the
commercial samples, and whether the DNA was broken down and to what degree.
Needless to say, the GM DNA inserts were not characterised at all.
The method of detecting GM DNA is highly flawed. It depends on amplifying a
small part - 180bp - of the entire GM DNA insert that was at least ten or
twenty times as long. So, any other fragment of the insert would not be
detected, nor would a fragment that did not overlap the whole 180bp
amplified, or that had been rearranged. The chance of getting a positive
result is 5% at best, and likely to be much, much less. Thus, a negative
finding with this detection method most probably does not indicate the
absence of GM DNA.
More revealing still, the researchers checked for GM DNA only in the gut
contents, but failed to check if the DNA has passed through the gut into
the blood stream and blood cells. This omission is inexcusable, as a series
of experiments in mice dating back to 1997 had already documented that GM
DNA can pass through the gut wall into the bloodstream, to be taken up by
cells in the blood, liver and spleen. When fed to pregnant mice, the GM DNA
also passed through the placenta to be taken up by the cells of the foetus
and the newborn.
In the first trial, the GM meal was fed to seven subjects that had part of
their lower bowel removed from a previous operation and wearing a colostomy
bag. The digested food from the colostomy bag was analysed, and GM DNA was
detected in all seven subjects. As much as 3.7% of the GM DNA was recovered
in one subject. Bearing in mind the limitation of the method used for
detecting GM DNA, all the values are probably gross underestimates.
In the second trial, the meal was fed to 12 human volunteers with intact
bowels. No GM DNA was detected in the faeces, which the researchers
claimed, indicated that the nucleic acid did not survive passage through
the complete intestine. But this claim is most likely to be false, due to
the limitation of the GM DNA detection method.
Microbes in the digested food that had passed through the small intestine
were cultured through 6 passages in broth containing glyphosate. Bacteria
grew to a density of 108/ml in each sub-culturing. In each sub-culture
derived from samples taken from 3 subjects at 180, 240 and 300 min after
eating, the transgene was found. This is yet another gross underestimate.
The method depends on the bacteria having taken up an intact gene coding
for glyphosate tolerance, and would not have detected bacteria that have
taken up fragments of that gene, or other parts of the GM DNA containing
other genes or gene fragments.
Although GM DNA was not detected in samples taken from these 3 subjects
prior to GM soya consumption, when the microbes in this material were
cultured in broth containing glyphosate, the transgene was detected in a
sample collected before the GM meal, though at very low concentrations.
This suggests that the subject may already have GM DNA in the gut prior to
the experiment, possibly from consuming GM soya. The bacteria harbouring
the transgene could not be isolated, so the researchers concluded that,
"although present, the bacterium represented a very small proportion of the
indigenous intestinal microflora". But as bacteria are capable of
multiplying, even rare gene transfer events cannot be ignored.
The researchers were disingenuous when they expressed surprise at the
relatively large proportion of GM soya DNA that has survived passage
through the small bowel. But in earlier research already published, the
same group had found that DNA in food or mixed up with food was much slower
to degrade than naked DNA.
Despite the severe limitations placed on detecting GM DNA, and an
experimental design both biased towards negative results, irrefutable
positive evidence was nevertheless obtained. That means the transfer of GM
DNA in the human gut could be much more extensive than the data indicate.
This makes it all the more astonishing for the FSA to have reportedly
claimed that "the findings had been assessed by several Government experts
who had ruled that humans were not at risk". Those experts should now be
named and made to defend their ruling.
In a statement on its website, the FSA said that the study had concluded it
is "extremely unlikely" that GM genes can end up in the gut of people who
eat them. This statement is highly misleading and very likely to be false.
Our government's scientific advisers have been guilty of persistent denial
in the face of mounting evidence that horizontal gene transfer can happen
and has happened. They are guilty of bad scientific research that misleads
the public, of downplaying positive evidence, and of taking the absence of
evidence as evidence of absence.
I first pointed out the dangers of horizontal gene transfer to MAFF in a
series of correspondence in 1996. Their scientific advisers said there was
no evidence it could happen. When it became clear that horizontal transfer
of GM DNA from GM plants to bacteria can readily happen in the laboratory,
the scientific advisors said "just because it happens in the laboratory
does not mean it will happen in the field". When positive findings turned
up in the only field monitoring experiment in the world that has ever been
performed, the scientific advisors dismissed that too, and explained it
away by a 'cautious' interpretation of the evidence.
This latest finding is the last piece of damning evidence that horizontal
transfer of GM DNA can indeed happen, has already been happening, and
cannot be controlled if GM crops continue to be released to the
environment. GM DNA, as opposed to natural DNA, is in many respects
optimised for horizontal gene transfer. Horizontal transfer of GM DNA can
create new viruses and bacteria that cause diseases, spread drug and
antibiotic resistance among pathogens, and trigger cancer by jumping into
genomes of mammalian cells. New 'pharm' crops are being developed that
poison our water and soil, affecting all organisms in our food web. The
ecological impacts are unthinkable. What more do we need for an immediate
comprehensive ban on GM crops?
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