We often hear about the virtues of a Mediterranean Diet and a recent study provides the first clear evidence that the diet may really be good for health. Here is what I wrote about this new work in the April edition of the Dorset-based Marshwood Vale Magazine:
There’s something very seductive about the idea of a “Mediterranean Diet”. It’s not just the food; it’s a life lived in the sunshine, near the sea, with family and friends, laughter, relaxed …… It’s not so far away now if you live in Dorset: there are olive stalls on Bridport and Wimborne markets, olive oil is readily available and there’s no shortage of fresh fruit and vegetables; not sure about the weather though. But is the idea of the “Mediterranean Diet” simply a marketing ploy or does it have some foundation in reality?
Let’s start by going back to the 1940s when the American scientist, Ancel Keys, heard about the apparent epidemic of heart disease among US business executives. This was a very well fed group of men and Keys wondered if, paradoxically, their “good” diet might be the source of their illness. He decided to investigate the influence of diet on health by looking at the incidence of heart disease (stroke and heart attack) in men from different countries and found a striking pattern: men in Southern Europe (especially Crete) were at much lower risk of heart disease compared to men from the US and Northern Europe. The idea that lifestyle and diet influenced the risk for heart disease arose from this study and by analysing blood samples from participants it was found that the level of cholesterol was an important risk factor.
The idea of a “Mediterranean Diet” developed from this work and reflected food typically consumed in the early 1960’s in the low risk countries such as Crete together with much of the rest of Greece and Southern Italy. As well as regular physical activity, the diet emphasises plant-derived foods (vegetables and legumes), fresh fruit, olive oil as the main fat source, dairy produce (cheese and yoghurt) in moderation, fish and poultry in low to moderate amounts and a few eggs. The diet has little red meat but wine is consumed in low to moderate amounts.
These kinds of study, where the influence of diet on disease is examined in different populations are called observational studies. They are very valuable in spotting trends but they cannot rule out other influences. To focus on the effect of diet, a more rigorous study design called a clinical trial is required and the results of the first full clinical trial of the effect of a “Mediterranean Diet” on health have just been released.
About 7500 men and women were recruited to the trial by doctors in Spain. Aged between 55 and 80, they did not have heart disease at the outset of the trial but they were all at risk for the disorder, either because of type 2 diabetes or other risk factors. They were assigned randomly to three dietary groups: “Mediterranean Diet” including 60 ml of olive oil a day, “Mediterranean Diet” including 30 g of mixed nuts (walnuts, almonds and hazelnuts) a day, “low fat” diet (starchy foods, fruit and vegetables, lean fish but avoiding vegetable oil, nuts and red meat). All participants were given regular advice on diet and their urine was analysed to check that they were following the diets. The two “Mediterranean Diet” groups found it easy and pleasant to stick to the prescribed eating pattern. This was not the case for the “low fat” group and their diet gradually changed in to one resembling a typical Western Diet.
The study was terminated early, after nearly five years, because the results were so clear cut and it would have been unethical to continue. It was found that the risk of suffering a heart attack or stroke was 30% lower in the two groups following the “Mediterranean Diet” compared to those on the typical western diet.
This is a striking result for several reasons. It had long been suspected that a “Mediterranean Diet” conferred health benefits but this is the first confirmation using a rigorous format where participants are randomly assigned to different diets and carefully monitored. The trial also uses real-world outcomes such as heart attack and stroke. Many studies have used so-called “surrogate indicators” such as levels of cholesterol; these are useful but do not tell you about the real-world effects of the diet. The effects of the diet are also comparable to those of the cholesterol-reducing drugs called statins but without the side effects. Moreover, the participants actively enjoyed the diet. For all these reasons there is great excitement about these new findings.
Of course there are still questions to be answered. The group of people studied were all at risk for heart disease and although we might suspect that the “Mediterranean Diet” would also protect low risk groups, we don’t yet have clear evidence. It would also be useful to know whether any specific factors in the diet had greater effects. There has been some speculation that it is the nuts and olive oil but this remains to be verified.
How should we respond to the results of the trial? The message is clear: following a “Mediterranean Diet” can improve cardiovascular health and we might all want to reflect on this in choosing what we eat. Many of the participants in the trial were already taking cholesterol-lowering statins and despite this the diet had a clear effect. So, if you are already taking statins, changes in diet may still help. It’s important to remember that the original “Mediterranean Diet” was part of a lifestyle which included regular exercise and where food was eaten for pleasure, not convenience, with family and friends often being involved. Perhaps underlining this idea, in 2010, UNESCO recognised the “Mediterranean Diet” as a style of eating embedded in the culture, tradition and way of life in these parts of Europe. So, some changes to diet may help but make sure you take exercise and make sure you enjoy your food!