Can the Mediterranean diet prevent heart attacks and strokes?

According to new research published in the British Medical Journal, people at high risk who follow a Mediterranean style diet may lower the chances of heart attack, stroke and early death when compared to ‘minimal intervention’ (for example, being given dietary advice).

The study also examined six other dietary programmes: low-fat, very low-fat, modified-fat, combined low-fat and low-sodium, the Ornish diet (a vegetarian diet low in fat and refined sugar) and Pritikin diet (a plant-based diet limiting processed food). As well as the Mediterranean diet, the only one to show benefit in comparison to minimal intervention was the low-fat diet, which reduced the risk of non-fatal heart attacks and death.

This was a systematic review, which means the researchers didn’t carry out new experiments. Instead, they analysed 40 different studies from the past and looked for patterns in them. In total, these studies involved over 35,000 participants who either had heart disease already, or were at risk of it, for example because they had conditions such as obesity or diabetes.

There’s a known link between what we eat and the risk of heart attack, stroke and death. However, when it comes to recommending specific diets or dietary patterns that could be helpful, there isn’t much research available. This study offers stronger evidence, and that may be welcome news for healthcare professionals and patients wanting more confidence in their chosen dietary programmes.

• Watch our video answering common questions about the Mediterranean diet

The BHF verdict

Tracy Parker, Senior Dietitian at the BHF, says: “It’s long been known that eating a Mediterranean-style diet is good for your heart, but it’s encouraging to see programmes like this lower the risk of death and heart attacks in patients already at risk of cardiovascular disease.

Whether you are at risk or not, a healthy lifestyle which includes a balanced diet can help you to lower your risk

"Whether you are at risk or not, a healthy lifestyle which includes a balanced diet like the Mediterranean-style diet can help you to lower your risk of developing heart and circulatory diseases. The risk factors associated with cardiovascular disease such as type 2 diabetes, obesity, high blood pressure and high cholesterol are also reduced with a Mediterranean diet.

“It’s easy to do – make sure you are eating plenty of fruit and vegetables, beans, lentils, wholegrains, fish, nuts and seeds, along with some low-fat dairy and fat from unsaturated sources like olive oil. It’s also important to eat less processed meat, salt and sweet treats.”

• Brush up on the most common sources of salt and sugar in the average diet

How good was the research?

This study used two related methods called systematic review and meta-analysis. In systematic reviews, several studies which looked at the same research question are grouped together and evaluated in a structured way. Meta-analysis is the statistical method used in a systematic review to combine the findings of those studies.

When it comes to gathering evidence on which interventions work and which ones don’t, high-quality systematic reviews are very reliable. Because they give a meticulous summary of multiple studies, systematic reviews are often more trustworthy than each study taken alone.

Another key strength of this research was that it used the ‘GRADE’ method to assess the quality of each study and the effectiveness of each dietary intervention. (GRADE is a method of assessing the certainty in evidence and the strength of recommendations in health care.)

However, the study also had some limitations. For instance, some of the studies looked at other treatments besides dietary programmes, such as drug treatment and stopping smoking. Although the researchers tried to consider this in their analysis, they couldn’t be completely sure it didn’t influence their findings.

In addition, the researchers couldn’t fully consider how well people followed the dietary programmes because that information wasn’t always documented in the studies they analysed.

One further limitation is that people in the ‘minimal intervention’ groups experienced a variety of support, ranging from no dietary advice to dietary counselling. In all studies, however, minimal intervention was less intensive compared to following a dietary programme, which sometimes included physical exercise and behavioural support as well.

How good was the media coverage?

This research was covered in news outlets including The Guardian, The Independent and The Mirror.

The Guardian offers a balanced take on the research, drawing attention to its weaknesses while making clear that the findings are robust enough to boost confidence in Mediterranean and low fat diets.

Helpfully, they quote the study authors as follows: “moderate-certainty evidence shows that programmes promoting Mediterranean and low-fat diets, with or without physical activity or other interventions, reduce all-cause mortality and non-fatal myocardial infarction [heart attacks] in patients with increased cardiovascular risk. Mediterranean programmes are also likely to reduce stroke risk.”

Similarly, The Independent and The Mirror both summarise the research accurately, describing the study design along with its key findings and main conclusions. The Independent headline gives a useful snapshot of the overarching message, with “Mediterranean diet can reduce death risk due to heart attack, stroke”.

Furthermore, The Mirror makes clear exactly which diets were included in this research, explaining potentially lesser-known ones such as the Pritikin diet and the Ornish diet.

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