There is no evidence of a clear benefit to heart health from fats commonly found in oily fish, researchers say.
Omega-3 fats are contained in oily fish and some seeds
Consumption of omega-3 fatty acids is thought to protect against heart disease and UK guidance advise eating up to four oily fish portions a week.
But the British Medical Journal review of 89 earlier studies looking at heart disease, cancer or strokes found no evidence the fats offered protection.
Heart experts said people should not stop eating oily fish, such as salmon.
The balance of evidence had suggested omega-3 fats decreased mortality, but then one large-scale trial came to a contradictory conclusion - changing the overall picture.
That trial looked at the impact of omega-3 fats on patients with chronic heart disease and suggested the fatty acid did nothing to prevent a recurrence of these conditions.
Looking at 3,114 men with stable angina in 2003 it found that those given high amounts of oily fish were at a higher risk of heart attack and recorded an increased number of cardiac deaths.
The authors could not say why the results of this trial differed from other large studies in the field.
They therefore concluded that it was not clear whether omega-3 fatty acids reduced or increased total mortality, cardiovascular events, cancer and strokes.
The team led by Lee Hooper, lecturer in the school of medicine, health policy and practice at the University of East Anglia in Norwich, said: "UK guidelines encourage the general public to eat more oily fish, and higher amounts are advised after myocardial infarction (heart attacks).
"This advice should continue at present but the evidence should be reviewed regularly.
"It is probably not appropriate to recommend a high intake of omega-3 fats for people who have angina but have not had a myocardial infarction."
Epidemiology expert Dr Eric Brunner, of the Royal Free and University College London Medical School, said for the general public some omega-3 was good for health.
"Whether omega-3 fat prevents cognitive impairment and dementia is currently being tested in trials, with the first results expected in 2008," he said.
"It seems that for healthy people the health advice remains well-founded but for people with chronic heart disease there is now a doubt."
Dr Mike Knapton, director of prevention and care at the British Heart Foundation, said people should not stop consuming omega-3 fats or eating oily fish as a result of this study.
"Until now, medical research has demonstrated a benefit from omega 3 fats in protecting people from heart and circulatory disease," he said.
"This systematic review of numerous studies concludes that there is no clear evidence either way.
"More research is needed to establish why some studies have shown a slightly increased risk associated with eating very high amounts of oily fish, which is possibly related to mercury levels."