Doctors will raise doubts today over the health benefits of eating oily fish, as recommended by the government, or taking Omega 3 supplements.

A review of the data, published online by the British Medical Journal, finds that Omega 3 fatty acids do not prevent heart attacks or cut deaths from heart disease. The health benefits are not clear from the evidence so far, the researchers say.

Those who eat most fish tend to be people with healthier lifestyles, they say. In most of the studies so far, the effects of better eating and more exercise have not been sufficiently allowed for.

The authors, Lee Hooper from the school of medicine, health policy and practice at the University of East Anglia and colleagues, say they do not rule out an important effect on mortality but more and better studies should be done, and the evidence should be reviewed regularly. The Food Standards Agency recommends that most people should eat up to four 140g portions of oily fish, such as mackerel, kippers, herring or salmon, a week. But girls and women who might become pregnant and breastfeed should eat no more than two and should not eat marlin, shark or swordfish because of the toxic substances they have ingested.

Omega 3 has been considered good for health for decades. It has been thought that a diet of oily fish was responsible for the low rates of coronary heart disease among the Inuit people. Dr Hooper and colleagues pulled together data from more than 15,000 studies and found 89 that were robust enough.

But when the data was pooled, there was no strong evidence that Omega 3 reduced the likelihood of a heart attack.