ICTSD Outputs and Activities on Biotechnology, Trade and Sustainble Development

Biotechnology: Addressing Key Trade and Sustainability Issues

B.1 Environmental, health-related and socio-economic considerations

Q1 Are GMOs harmful to human health?

Although the impact of GMOs on human health is one of the most frequently cited reasons for opposition to biotechnology, existing studies have so far not yielded scientifically conclusive evidence indicating that GMOs have harmed human health. Proponents of the technology also point out that GMOs have been produced and consumed for over ten years without confirmed cases of harm. However, critics counter that not enough long-term studies have been conducted on the subject to provide a conclusive answer on the potential future health impacts of GMOs. Experts in risk assessment point out that no food, or for that matter any course of action, is without risk; the questions are therefore whether food containing GMOs presents unique risks to human health, what likelihood of harm these risks present, and how serious the impact of any such harm would be. Fears expressed regarding the health impacts of GMOs include the potential for allergens to be introduced into the diet, higher levels of toxicity, uptake of transgenic DNA by humans, increased resistance of bacteria to antibiotics and unintended side-effects.

The insertion of a gene from one plant into another has led to concern that consumers will buy and consume a food without being aware that it includes genes from another organism which they could be allergic to. For example, a gene from a peanut could be inserted into a maize variety, leading to allergic reactions in consumers with peanut allergies that were unaware that the maize contained peanut genes. Concerns over allergenicity have led to standard allergenicity testing being implemented before the commericalisation of GM crops around the world (see Section C.6).

In addition, adverse direct health impacts could stem from higher or lower levels of naturally occurring proteins, toxins or other harmful compounds in foods resulting from genetic modification. While conventional toxicity testing could address this, methodological challenges in testing the toxicity of whole foods through animal tests – witnessed in the public controversy over Pusztai’s rats (see Biotech Headline 1) – have led to the development of alternative ways of testing the safety of GM foods (WHO, 2005).

The potential for gene transfer from GMOs to humans has also been raised as an area of concern. Research has shown that DNA in food is not completely broken down by digestion and that small fragments of DNA from food can be found in different parts of the human gastrointestinal tract after eating, although the pieces are usually too small to be functional. However, even if sufficiently large pieces of DNA survived, the process of taking up the genes and functionally integrating them into human DNA would be extremely complex (Donaldson and May 1999; Royal Society 1998b). It has also been noted that DNA in food is consumed daily without any evidence that intact genes are transferred to humans.

In a related but separate scenario, the antibiotic resistance marker gene – which is included in the gene ‘package’ because it can survive the addition of antibiotics and thereby allow scientists to identify organisms that have been genetically modified – could be taken up by gut bacteria and lead to resistance of these bacteria to antibiotics. While gene transfer to micro-organisms is thought to be highly unlikely, the possibility cannot be ruled out and there is general agreement that the use of such marker genes should be restricted, in particular if the antibiotic is an important medication (FAO/WHO, 2001). Also, the widespread use of antibiotics as feed additives for animals and medicines for humans is thought to carry a far greater risk of creating antibiotic-resistant bacteria than the transfer of marker genes (Royal Society, 1998b).

As conventional breeding of plant varieties has been known to cause unexpected effects on the genetic structure, performance and characteristics of plants, it can also be expected that the insertion of one or more gene packages into a plant can cause similar effects. These effects can include changes in the DNA structure and the silencing or increased expression of genes. For example, the newly inserted gene and its accompanying elements might interact with the other genes in the organism and either create new characteristics, or stop the functioning of other characteristics (Wilson et al., 2004). Methods to assess the potential of unintended effects in particular GMOs are being developed (WHO, 2005).

BIOTECH HEADLINE 1: Pusztai's Rats

In April 1998, Arpad Pusztai, a researcher at the Rowett Research Institute in Aberdeen, UK, announced that a ten-day experiment he had performed had revealed that GM potatoes caused intestinal inflammation in rats. Controversy followed as civil society groups pointed to the research as scientific proof of the dangers posed by genetic modification. Problems with the conduct of the experiment soon surfaced, however, leading many in the scientific community to criticise his results and conclusions.

The experiment involved groups of rats who were fed parent (regular) potatoes, potatoes spiked with lectin and potatoes genetically modified to produce lectin. Lectin is a protein important in many plants’ natural defences that could be used to improve their resistance to insects. Pustzai fed different groups of rats raw or boiled potatoes from each of the three groups. He examined the intestines of the rats after ten days and found that the length of a key part of the rats’ intestinal system known as the jejunal crypt was longer if they had been fed with raw GM potatoes compared to rats fed with raw parent and parent+lectin lines. He also found that the walls of the caecal – a portion of the large bowel which receives faecal material from the small bowel – was thinner in the rats fed with boiled GM-potato than those fed with boiled parent and parent+lictin lines.

Pusztai presented preliminary findings, which had not yet been peer reviewed, on a popular UK TV show on 10 August 1998, making claims about the effects of GM potatoes in distorting rat digestive systems that his critics felt could not be substantiated by the data he had gathered. Shortly afterwards, he was suspended by the Rowett Institute and his research was subsequently subject to an audit. After over a year of speculative controversy in the press and scientific community, the scientific journal The Lancet decided to publish the research with the disclaimer that it was doing so in order to ensure the paper was in the public domain, but that many of the findings of the study, the process and the data were “flawed”.

Various criticisms have been levelled at the experiment, including by the British Royal Society. Firstly, scientists have long known that many lectins are especially toxic and can cause intestinal damage. Pusztai had chosen the particular lectin (“snowdrop” GNA lectin) because his earlier studies had shown that such damage would be minimal. However, Brian Fenton from the Scottish Crop Research Institute, an institute that Pusztai co-operated with, described an experiment where the GNA lectin did in fact trigger adverse biological effects, and could thus be used to explain some of the results in the rats. In addition, there were several differences in composition of the different potato types, including macro and micronutrients, toxins, protein content (which was added separately, possibly causing other distortions in the results) and a lack of testing for various toxins. Reviewers also suggested that raw potatoes are not an ideal diet for any animal and could have caused data distortions.

Overall, many scientists found that there were too many other variables that could be responsible for the minor digestive differences viewed in the different groups of rats. Moreover, judging the safety of GM food products on the basis of experiments involving one species of animals, fed with one product modified by inserting one gene by one method was thought to be unjustifiable even for the best-designed research.

Sources: Ewen & Pusztai (1999); Royal Society (1998a); Storzek (1998).