Scientists have published the first study that casts doubt on some of the health benefits of fish oils - and say that daily doses may actually increase the risk for people already suffering heart disease.

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• Omega 3 fatty acids contained in oily fish such as salmon and tuna have long been hailed a “super food” which plays a key role in boosting our immune system, staving off heart attacks and cancer as well as increasing brain power.

  

  Tuna are rich in Omega 3 fatty acids, but are also under threat from overfishing

  But the latest study finds little evidence to support the more extravagant claims and experts discovered that angina sufferers may put themselves at higher risk by taking fish oils.

  The authors say that people in developed countries already have access to plenty of Omega 3 fatty acids in their diet, while people in poor countries were being deprived of essential oils and proteins by foreign fishing fleets.

  They warned of an environmental catastrophe as ocean stocks are squandered due to the massive demand for fish - on the advice of medical experts and nutritionists in the West.

  Prof Daniel Pauly, of the University of British Columbia and one of the authors, said: “The food security of people in the developing world should not be depending on the whim of food fashion, which is what drives this ‘fish have omega 3s which are good for you’ in rich countries.”

  Over the years, fish oils have been credited as helping with everything from rheumatoid arthritis, to fighting obesity, diabetes and even the menopause.

  The paper, compiled by seven different authors, questions previous findings that fish oils promote good health and says more research is needed to prove that fish oil is essential for good health.

  It cites a study of men suffering angina - chest pains linked to poor blood flow to the heart – which found those who took fish oil were shown to be at greater risk of dying from heart disease.

  The report says: ”The evidence for the comprehensive benefits of increased fish oil consumption is not as clear-cut as protagonists suggest, including the strongest evidence to date that indicates a 15 per cent benefit in the prevention of cardiovascular disease, which may itself may be reduced further if sustainable lifestyle changes were adopted as currently recommended.

  ”The evidence is even less convincing for the benefits of fish oil to growth and brain development in infants, mental health and the prevention of dementia, cancer, inflammatory bowel disease and diabetes.

  ”Even if the evidence were more compelling, the development of dietary guidelines that may have large-scale environmental consequences, does not seem wise.”

  The controversial findings have appeared in a paper published in the Canadian Medical Association Journal and have already triggered a critical reaction from health experts.

  John Stein, professor of physiology at Oxford University who has made particular study of fish oils in the brain, said the evidence for fish oils being beneficial to the body for a wide range of reasons was stronger than the study gave credit for.

  He said: “Most people are in agreement that heart disease is reduced by 20 per cent in fish eaters and up to 37 per cent in people eating at least two portions a week.  This is better than statins, the drugs that lower cholesterol, and with none of the side effects.

  “Pregnant mums eating oily fish increase their child’s IQ even when all potential factors such as income, class and education are adjusted.  And our own studies show you can improve reading and attention in children with oily fish.

  “There is also growing evidence in the scientific literature that fish oils can reduce antisocial behaviour -  which this study does not quote.  There are few large studies on fish oils because you can’t patent them so no drug company is interested.  That doesn’t mean there is no effect!”

  Prof Michael Crawford of the Institute of Brain Chemistry, London Metropolitan University, another advocate of Omega 3s in the diet, said:

  “From the very start of animal evolution 600 million or so years ago to present day cephalopods, fish, amphibians, reptiles, birds, mammals, apes and humans the same Omega 3 fatty acid, DHA, has been used in eyes and brains.

  “Nature found no alternative in over 600 million years of evolution. That is the most compelling evidence for the absolute requirement for DHA in the building and function of brains and eyes.”

  As well as questioning the effectiveness of fish oil, the study asks whether it should be promoted as an essential supplement when fish stocks are in long-term decline.

  Global demand was putting massive pressure on developing countries to either allow powerful foreign fleets into their traditional waters or to export their catches to foreign markets.

  Poor communities, already suffering from poor nutrition and health, were being deprived of an important source of protein which – ironically – was being sent instead to richer countries where obesity and lack of exercise was causing major health problems.

  The study suggests that until alternative sources of Omega-3 – from plants, algae and yeast – are developed commercially it would be more responsible to stop advocating the use of fish oils.

  Britain’s Food Standards Agency is currently reviewing its recommendation that people eat two portions of fish a week on health grounds, one of them oily fish, because of global concern about fish stocks.