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Assessment & Impacts » Health

Title: GM Foods: Potential Human Health Effects
Source: CAB International
Publication date: September 01, 2003
Posting date: July 01, 2004


Arpad Pusztai, the scientist who first stunned the world with research
claiming that GM crops might damage human health (and who lost his job as
a result), has released new findings that further support his early

Dr. Pusztai said that the work carried out by biotechnology companies on
the human health hazard from GM food is inadequate. He said to date there
have never been any human clinical trials conducted on GM food. Most
attempts to establish the safety of GM food have been indirect and there
is absolutely nothing known about the potential hazards (if any) for
human health of indirect exposure to GM foods such as through consumption
of animals fed on GM food.

In a chapter published in a book on food safety, he brought together all
the scientific studies carried out into the safety of GM foods and
subjects them to rigorous statistical and scientific scrutiny.

Though he found most of the studies were inadequate and wanting in terms
of the quality expected, he nonetheless were able to find that some
existing studies support the early warnings he expressed from his own
research in which he found rats fed on GM potatoes suffered a weakened
immune system as well as severe impairment in the development of the
internal organs. He concluded that "the present crude method of genetic
modification has not delivered GM crops that are predictably safe and

Some of the conclusions that could be drawn from his review of the
existing studies - both peer-reviewed as well as non-peer reviewed but
have implications for regulations - are as follow:

In a feeding experiment commissioned by Calgene for the US Food and Drug
Administration (FDA) involving GM tomatoes (Flavr Savr) to rats, seven
out of 40 rats which ate GM tomatoes died within 2 weeks. The nature of
these deaths was not specified in the study but the evidence that they
were not related to the ingestion of transgenic tomatoes was

The conclusion from the Flavr Savr experiment that feeding rats on GM
tomatoes for 28 days had no effect on weight gain, feed intake and organ
weights could not be justified because the starting weights of the rats
were so widely different that finding significance differences in weight
gain, feed intake and organ weights was not likely. The FDA conclusion
that Flavr Savr presented no more dangers to consumers than ordinary
tomatoes therefore does not appear to rest on good science.

With regards to evidence presented by Aventis for the two lines of Chardon
LL herbicide-resistant GM maize seed to establish their substantial
equivalence to the conventional parent maize line, the company did not
specify the origin and conditions of cultivation of the different GM and
non-GM samples and therefore strict scientific comparisons could not be
made between them. However, even under these conditions, the two lines of
GM maize expressing the socalled PAT-PROTEIN showed many statistically
significant differences in fat and carbohydrate contents in comparison
with the non-GM grain samples, and fat, protein and fibre between silage
samples from GM and non-GM maize. Thus, the conclusion that GM maize is
not "materially different" from current commercial varieties cannot be
regarded as valid.

An experiment was also conducted whereby PAT-PROTEIN was given to
rats for 14 days to assess the cumulative toxicity of the protein and to
provide a rational basis for toxicological risk assessment in humans.
But the design and execution of the experiment was faulty therefore it is
difficult to draw valid conclusions from the feeding study. The results
therefore could not be taken as evidence that the transfer of its gene
into maize represented no risk for the rat and by inference, for humans,
particularly as no gut histology studies have been completed so far. In
addition, a recent publication has showed that DNA survived in intact
form or slightly fragmented unless the GM maize was heat processed
extensively. Therefore, the possibility exists that with underprocessed
maize products, humans and animals might be exposed to the DNA
used in genetic engineering.

On the publications establishing the compositional "substantial
equivalence" of GM and non-GM soya, it has been found, on closer study
of the data, that the statistical comparison of the macronutrients of GM and
non-GM lines was not scientifically valid. Pusztai found that there is
insufficient evidence to date to decide whether the composition of GM and
conventional soybeans is equivalent or not. Because not strictly
comparable compositional data were used, the case for equivalence was not
properly established.

Milk production and composition and performance data in the lactating cow
study showed some significant differences between cows fed diets
containing the different lines of soybean, indicating a lack of
"substantial equivalence".

In a main histology study carried out on the ileum of mice fed with
potatoes transformed with a Bt var.kurstaki Cry1 toxic gene, it was
established that, in contrast to general belief, exposure of the mouse
gut (ileum) to the Cry1 gene product has caused profound hypertrophic
and hyperplastic changes in cells of the gut absorptive epithelium and
can lead to mucosal sensitization.

The chapter, coauthored by Pusztai, together with S. Bardocz and S W B
Ewen is found in the book "Food Safety: Contaminants and Toxins", edited
by J P F D'Mello of the Scottish Agricultural College in the UK and is
available online at:

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