As the list of genetically modified foods expands, so the level of consumer anxiety burgeons. Simon Midgley looks at the causes of public concern. As the list of genetically modified foods expands, so the level of consumer anxiety burgeons. Derek Burke (far right) explains why altered foods were allowed on to supermarket shelves.

When the first genetically manipulated vegetarian cheese and tomato paste appeared on supermarket shelves shoppers seemed unconcerned. But the second wave of modified foods has been engulfed in controversy.

The dispute hit the headlines earlier this year when it emerged that a soya bean genetically modified to resist herbicides was entering the food chain without being labelled as such. The news infuriated consumer and environmental groups.

The biotechnology industry had promised the public that consumers would be given information enabling them to make a choice about whether or not to buy genetically modified foods. But because Monsanto, the American company responsible for the modified soya bean, grew it alongside ordinary strains it was impossible to separate the two. Nor, under the European Union regulatory framework, are there any regulations preventing mixed growing of crops.

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The EU Commission is now presenting new proposals on how genetically manipulated soya - and soya goes into 60 per cent of all processed foods - should be labelled. But the European biotechnology industry is exasperated with Monsanto because it considers that it has undermined the confidence-building exercise it had embarked on to persuade consumers of the advantages of genetically altering food.

Consumer anxiety also surrounds the arrival of maize genetically modified to include a bacterial gene with a remarkable ability to fight insects. Unfortunately, in order to insert this gene, scientists at the pharmaceutical company Ciba-Geigy also modified another gene in the maize that confers resistance to the antibiotic ampicillin.

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The Government's Advisory Committee on Novel Foods and Processes, which considers minor research trials of genetically modified plants, recommended that Ciba-Geigy's maize should not be cleared for human consumption because there was a small risk that it could undermine the effectiveness of antibiotic treatments. Another government committee, however, the Department of the Environment's Advisory Committee on Releases to the Environment, which considers field trials and exploitation of genetically modified plants, decided that it was unlikely that the gene would be transferred to people.

Faced with these conflicting arguments, the British government decided to vote against permitting the introduction of the genetically modified maize into the EU. But the Commission overruled Britain and several other European objectors because it agreed that the risk to people was slight.

Against such a confused background the Government's Panel on Sustainable Development has warned that the regulatory framework governing the release of genetically modified organisms into the environment may be inadequate. Tne warning has prompted the Nuffield Council on Bioethics, an independent body which examines the ethical issues raised by developments in medicine and biology, to set up a working party on the genetic modification of plants for human consumption.

David Shapiro, executive secretary of the Nuffield Council, says that the arguments over Ciba-Geigy's maize indicate "that regulation of these matters is a mess" and needs to be overhauled. It is an important issue, he adds, because genetic modification of soya and maize are the first tiny steps in a process that could have far-reaching implications for improving the world's capacity to meet its future food needs. "The real prize is the notion that you might be able to engineer plants genetically that could grow under drought conditions or in saline soil. When it comes to feeding 15 billion people 50 years on, that would be a very serious prize."

The Nuffield working party is to be led by Alan Ryan, the warden of New College, Oxford. Ryan says: "The hope is that we end up making recommendations about how the regulatory system should work and whether the current system should be modified."

Concerns about genetically modified plants fall into two categories. The first consists of fears that not enough research has been done into the consequences of their introduction into the environment. These include worries that genes might cross the species barrier and create super resistant varieties of weeds and insects; that dominant single strains of plants could emerge that might be then vulnerable to some viral threat; that there is a danger of compressing genetic variety and that biotechnology may give agro-chemical companies unwarranted power in Third World nations.

The second category of anxieties is partly rooted in the public's deep unease about altering nature. "I think there is a sense that the system keeps on getting caught on the hop," Ryan says, "and that people have anxieties of a kind they cannot quite put a name to. I am deeply curious about what people feel is natural and unnatural and whether it matters and if so how it matters. Why is it that we do not care about some sorts of obvious tinkering with nature, while some tinkering with nature seems to unnerve us? What is behind the unnerving and what can government do to address it?"

Genetically modified food: the scientific rationale

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CHEESE

Vegetarian cheese was the first genetically modified (GM) food to come to the market in 1991. Traditional cheese manufacturers used a crude preparation of the enzyme chymosin, called rennet and obtained from calves, to coagulate the milk. But the crude enzyme was variable in its effect and was gradually replaced by a similar enzyme made in bacteria, and then by a genetically engineered enzyme. This was possible because the gene for chymosin had been cloned. Initially the cheese was not labelled because the enzyme was identical in every way to rennet. One retailer did decide to label it as suitable for vegetarians, since no animal product had been used in its manufacture. This was the first example of a GM food that offered an advantage to the consumer.

TOMATO PASTE A second successful product was tomato paste made from GM tomatoes. In tomatoes the enzyme polygacturonase is responsible for the breakdown of the cell wall and the pectin that leads to softening and ultimately disintegration. In 1994, the Advisory Committee on Novel Foods and Processes (which I chaired) received a submission for a tomato paste made from a GM tomato in which synthesis of this enzyme had been slowed down. This enabled the fruit to ripen normally but to soften slowly. The tomato did not have to be picked so early, the fruit could be transported with less damage and, because of the higher levels of pectin, the eventual paste was more naturally viscous. The company chose to market the paste, rather than the whole fruit, to avoidcomplications about consumer concerns over eating the DNA from the seeds. My committee recommended approval of the modified tomato, despite it containing an antibiotic resistance gene, because the gene was controlled by a plant promoter, and therefore could not work in gut bacteria, and because the antibiotic, kanamycin, was not of great clinical significance. The company concerned also worked with supermarkets to label the genetically modified tins of paste.

SOYA BEANS In plants the first genes to be manipulated were the herbicide-resistant genes. This development has been criticised, and is often put down to a "plot" by companies to increase their sales of herbicides. It is true that such an opportunity exists. However, the main reason these genes were selected was that the genes for herbicide resistance are single genes and therefore much easier to isolate and manipulate than the multi-gene complexes responsible for traits such as drought resistance.

A number of products from several herbicide resistant plants were approved by my committee but difficulty arose over soya beans from the Monsanto company which were resistant to the herbicide glyphosphate. Glyphosphate works by inactivating an enzyme in the plant essential for the production of complex amino acids, thereby preventing growth. By introducing a gene from an agrobacterium into a commercial variety of soya, the bean was made resistant to the herbicide.

We had no safety concerns over the product, which is the flour rather than the beans, since the DNA would be degraded during production. Nor did the product need to be labelled, although information was provided, on a voluntary basis, by the retailer. However, the retailers were unable to offer customers choice because the GM soya was not segregated from "normal" soya at source. Soya is grown in the US Middle West, where farmers grow different varieties of soya in the same field. So segregation would mean complete separation from start to finish: cleaning out the harvester between harvesting different varieties, using separate trucks to separate elevators, using separate rail wagons to the ports etc. This explanation of the difficulties was not accepted by consumers, who organised several boycotts.

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Maize GM maize developed by Ciba-Geigy contained, in addition to a bacterial gene that confers resistance to the European corn borer insect, and a gene that confers resistance to the herbicide glufosinate-ammonium, a third gene that confers resistance to the antibiotic ampicillin. We were worried that there might be a risk of transfer of this antibiotic resistance gene into gut bacteria when the maize was used for animal feed in an unprocessed form. The technical risk was certainly small; the consequential risk could have been large. We did not recommend approval but were later overruled in Brussels.

Derek Burke chaired the Advisory Committee on Novel Foods and Processes for nine years.

Our GM future: what will biotechnology produce next?

For plants, roughly chronologically: Identification of genes (genetic typing) responsible for desirable traits and their transfer to other species, for example between cereals.

Continued development of GM plants resistant to herbicides, viruses, bacteria and fungi.

Development of fruit and vegetables with longer shelf-lives and better shipping characteristics.

Modification of fatty acid synthetic pathways to produce oils containing more suitable fats and starches for either dietary or industrial use.

Improving the flavour, texture and nutritional content of fruit and vegetables through genetic modification.

Isolation and utilisation of more complex genetic systems - such as those controlling salt tolerance and drought resistance - making possible the production of plants that can be grown in a wider variety of habitats.

Manipulation of the genes that control flower shape and colour for the horticultural industry. Recently a gene has been identified that makes stressed grass stay green longer.

Isolation of the genes that control the plant's response to day length, and modification of these genes to produce plants that mature more quickly, so pushing north, eg, the boundaries for growing rape in Canada.

Developments in animals will be slower, for public concerns are much more serious. But some predictions are possible: Development of rapid genetic typing techniques will revolutionise animal breeding, enabling identification of the genes critical for elite stocks and their transfer by conventional breeding to others.

The identification of genes for undesirable traits will accelerate our ability to remove them from breeding stock.

Better understanding of infectious disease pathogens should lead to the ability to breed animals with increased disease resistance.

Genes could be introduced to enable cows to produce milk that is much closer in its composition to human milk for feeding to babies.

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A similar approach could be used to produce transgenic animals with, for example, less body fat.

Derek Burke