The first genetically modified foods with direct benefits for human health should be available within four years after successful experiments in the United States.

A GM soya bean that can help to prevent heart attacks has passed the first phase of trials, clearing the way for its use in foods such as spreads, yoghurts, cereal bars and salad dressings.

The research, at the University of South Dakota, has shown that oil from the GM soya can raise blood concentrations of long-chain omega3 acids, which are found chiefly in oily fish such as salmon, trout and fresh tuna. They protect against cardiovascular diseases and diabetes and help the growth of brain cells in the young.

Omega3 acids are regarded as so important that the Food Standard Agency (FSA) recommends a portion of oily fish every week, although 70 per cent of adults ignore the advice.

Efforts to promote fish consumption have raised concerns about fragile marine stocks, but the GM soya offers a sustainable, fish-free way in which people can maintain a diet rich in omega3 fatty acids.

More than 280 million acres of GM crops are already grown worldwide, but they are modified to resist weeds or insects. In Britain their reception has been lukewarm. The GM soya beans could change that attitude. The biotechnology company Monsanto has harvested 600 tonnes this year from trial plots in the US and some of this has already been passed on to food companies to develop products.

Monsanto expects the US Food and Drug Administration to clear it as a food by 2011, allowing it to reach American supermarket shelves by 2012. If it is approved by the European Food Safety Authority and the FSA’s novel foods committee, products containing the omega3 oil could then be exported to Britain.

Any product would be clearly labelled as GM, in the US and Europe. “We’ll want to label it,” said David Stark, Monsanto’s vice-president for consumer traits. “Consumers will have a choice: some may choose not to try it, but others will.”

He added: “It’s another reason for consumers to pause and consider whether GM has a role to play. I think it does, not only for how we deliver food for the planet, but also for how we protect our own health. We’ve shown for years that GM crops can control pests. That’s important to consumers, but not in a personal way. Hopefully this will be personal enough to make a difference.”

If it is passed by regulators, the soya oil would become the first beneficial food to be produced by genetic modification. It is much further ahead in development than the GM tomatoes announced last week by scientists at the John Innes Centre in Norwich, which are rich in an antioxidant thought to have anticancer properties. The tomato has so far been tested only on mice, but the soya has completed a trial, led by William Harris, professor of medicine at the University of South Dakota, on 33 volunteers.

The study, published in the journal Lipids, found that the GM soya oil increased the “omega3 index” in the participants’ blood from an average of 4 per cent to 5 per cent. Such a change, which was not seen in people taking normal soya oil, would be associated with a drop of about 50 per cent in the risk of heart attacks, Professor Harris said.

“We saw these effects in our subjects after just a few weeks. I can imagine that, if you got this into the food supply and people were eating it year after year, you do have an opportunity to raise omega3 levels in the blood.”

Professor Harris is now conducting a larger study, involving 250 volunteers, which will finish next month. He will also test food products containing the soya oil as they are developed.

The two long-chain omega3 fatty acids required by the body are eicosapentaenoic acid and docosahexaenoic acid. They are produced by algae and enter the human food chain through the fish that feed on them. The GM soya is enhanced with fungal and plant genes.

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