Not so long ago Dr Christopher Preston, a Senior Lecturer in Weed Management at the University of Adelaide, told the readers of CS Prakash's listserv, AgBioView, that the reason that there were so few published peer reviewed studies showing the safety of GM crops was simply that nobody was interested in publishing "negative results".

But now Dr Preston has somewhat changed his tune. He's now claiming that there are, in fact, many more such studies than had previously been admitted.

Dr Preston's new line of argument has been well received. Preston's list of "Peer Reviewed Publications on the Safety of GM Foods" is now prominently promoted on the homepage of Prakash's AgBioWorld website. And Monsanto has joined the chorus of approval:

We noted the excellent contribution by Dr. Chris Preston, "Peer Reviewed Publications on the Safety of GM Foods," AgBioView, Dec. 3, 2004.

For those readers interested in a more exhaustive list of animal feeding studies with crops derived from biotech crops, we provide below a reference list organized by animal species, transgenic crop group and by author.

This extensive database of feeding studies also supports the conclusion of Dr. Preston --"The overwhelming majority of publications report that GM feed and food produced no significant differences in the test animals." This information also can be found via Monsanto's website at

- Eric Sachs and Gary Hartnell, Monsanto Company, St. Louis, Missouri

But neither Preston's list nor Monsanto's bear serious scrutiny. Hartmut Meyer (coordinator of the GENET listserv) writes of Monsanto's "extensive database of feeding studies":

"Please note that most of the cited references in the document Monsanto is posting are abstracts or conference contributions. I found less than 30 references on these impressive 13 pages that appear to be published in "sound science" journals."

And Dr Arpad Pusztai goes still further (see below) in dissecting Preston's claims.

Preston says, "The report by Pryme and Lembcke (2003) described 10 such [published peer reviewed] studies. This report and the small number of studies is often quoted by groups opposed to the use of GM crops as justification for banning their use in the food chain..." But Preston says he has uncovered a series of publications that "were not captured by Pryme and Lembcke (2003)".

In total, Preston says, he has found 42 publications, the vast majority of which found no harmful effects from GM crop products. However, Arpad Pusztai, a leading expert in this field, points out that most of these studies are totally useless when it comes to evaluating food safety.
Dr Arpad Pusztai:

Regarding Christopher Preston's piece, my comment is of course that Pryme & Lembcke's cut-off point was at the end of the first third of 2002, probably somewhere along no 16 on Preston's list (to the best of my knowledge).

The next comment is that they looked at academic as opposed to production studies. These latter have very little scientific value; we used to call them at the Rowett Institute: "feed them and weigh them".

The next point is that my Nutrition and Health (2002) paper is not a review but, rather interestingly, Dr Preston did not mention our 2003 review that was published just at the same time as the Pryme & Lembcke review (even though I gave the reference to it in my previous comments on his assertions that he must have received because he did publicly respond to one of the points) but which also included more papers with analytical comparisons between GM and parent lines.

I think Dr Preston's list is quite revealing in terms of his scientific approach to this topic, particularly as regards the failure to distinguish between a scientific study and an animal production exercise. When I was asked by Professor Mosenthin to write my next review (to be published next year) he emphatically asked me to leave out all production studies from the review as these may be of some value to commercial animal production but have limited scientific value.

I give you a preview of what I wrote on this subject in my review:
1.1. Regulatory and general considerations

Assessing the production potential and value of feed components is of considerable commercial and practical importance. Indeed, in addition to safety and other nutritional considerations the effort spent by feed technologists on evaluating the feeding value of crops is considerably more extensive than that by human nutritionists to establish the nutritional value of foods for the public. Not surprisingly, this distinction is even more acute between genetically modified (GM) food or feed ingredients.

Thus, except the very recently published human trial with a single dose of GM soybean-containing meal (Netherwood et al., 2004), the almost total absence of published data in peer-reviewed scientific literature indicates that the safety of GM foods rests more on trusting the assurances given by the biotechnology industry than on rigorous and independently verified risk assessment. A comment in Science described this in its title: "Health Risks of Genetically Modified Foods: Many Opinions but Few Data" (Domingo, 2000). Indeed most of the attempts to establish the safety of GM food have been indirect using animal trials with GM feed ingredients and drawing inferences from these for human health. However even these animal studies in most instances had limited, mainly commercial objectives as it is obvious from recent reviews (Faust, 2002; Aumaitre et al., 2002).

Despite this, the main stated objective of the GM regulation is to assure the human population that GM foods are safe while animal safety is seldom discussed. The regulators, particularly in the USA, use a decision tree approach in which the authorities review the data usually provided by the biotechnology companies but do not carry out safety assessment of their own (Faust, 2002). Even in Europe the preferred approach is to use compositional comparisons between the GM crop and its traditional counterpart and if these results show no significant differences they are considered to be "substantially equivalent", meaning that the GM is as safe as the non-GM crop.

However, even though existing legislation does not require the testing of GM crop-based feedstuffs with target animals many new GM crops have been tested with farm animals but most of the time only to establish their effects on nutritional performance, digestibility, wholesomeness and feeding value for obvious commercial considerations (Aulrich et al., 2002; Aumaitre et al., 2002). In most of these relatively short term and rather empirical studies the emphasis was on productivity rather than on investigating the biochemical and cell biological interactions between the GM ingredient and the digestive tract, the effect of the GM DNA and protein on the gut epithelial cellular and tissue structure, its immune and endocrine systems and bacterial ecology. This is particularly regrettable because nutritional parameters, though of great commercial interest, are rather crude measures in physiological terms of the effects of GM ingredients and may give science only little guidance on what will be the likely biological consequences of long term and heavy exposure to GM crops.

Thus, as GM regulation is at present based on rather minimalistic legislative and scientific foundations, with the likely progress in future of our understanding of the biological principles underlining the whole GM business, major efforts of clarification and updating will in time be needed.

So here you have it. Coming back to Dr Preston's list. Actually there were only 41 and not 42 articles as he stated in his list. In his list these are the commercial studies: 2, 10-14, 17-18, 20-21, 23-24, 26-33, 38-40; 23 out of 41 leaves us with 18. I have to confess that I cannot read Russian or Chinese (neither can Pryme & Lembcke and I expect Dr Preston) so I could not read articles 7, 15, 36 and 41. So we are now down to 14!

Actually, Dr Preston missed two Malatesta papers, perhaps because they both show bad effects on the liver and the pancreas of mice fed RR soya, and quite a few others, but for these he will have to read my new review next year.

Finally, may I say that it would be in the interest of science if Dr Preston addressed and cleared up the reasons for the differences that I previously drew attention to between the actual data in the MON 863 study and his account of that study.

[for Dr Pusztai's previous comments on Preston's claims, see ]