Mediterranean and low fat dietary programmes reduce the likelihood of death and heart attack in patients at heightened risk of cardiovascular disease, finds the first comparative review based on randomised trials of seven popular dietary programmes.

The mediterranean diet which is rich in olive oil, nuts, seafood, whole grains and vegetables has previously been linked to a number of benefits. It has been known to reduce major cardiovascular events such as heart attacks (myocardial infarction) and strokes, as well as help healthy people to live longer. But any beneficial impact on death has still remained uncertain.

The study, led by an international team of researchers and published by The BMJ, showed that mediterranean and low fat dietary programmes "probably reduce the risk of mortality and non-fatal myocardial infarction in people at increased cardiovascular risk".

The review of 48 trials involving 35,548 participants showed that mediterranean dietary programmes were better than minimal intervention at preventing all cause mortality (17 fewer deaths per 1,000 over five years), non-fatal heart attack (17 fewer per 1,000) and stroke (seven fewer per 1,000) for patients at intermediate risk of cardiovascular disease.

While mediterranean dietary programmes also showed reduction in stroke risk, other dietary programmes showed little or no benefit over minimal intervention (eg. usual diet or brief dietary advice from a health professional), said researchers, including from universities of McMaster in Canada and Texas in the US.

Low fat programmes were also superior to minimal intervention with moderate certainty for prevention of all cause mortality (nine fewer deaths per 1,000) and non-fatal heart attack (seven fewer per 1,000).

The absolute effects for both mediterranean and low fat programmes were more pronounced for patients at high risk of cardiovascular disease (36 fewer all-cause deaths per 1,000 and 39 fewer cardiovascular deaths per 1,000 among those that followed the Mediterranean dietary programme over five years).

The five other dietary programmes generally had little or no benefit compared with minimal intervention typically based on low to moderate certainty evidence.

The researchers also acknowledged several limitations, such as being unable to measure adherence to dietary programmes and the possibility that some of the benefits may have been due to other elements within the programmes like drug treatment and support to stop smoking.