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Proof that Mediterranean diet has health benefits

By Lilian Anekwe

Older people who are at risk of heart problems, but have not had a heart attack or stroke, can lower their chances of having these problems by eating a ‘Mediterranean diet’, a new study suggests.

What do we know already?

The Mediterranean diet typically includes olive oil used as a main cooking oil; lots of fruit, nuts, vegetables, and cereals; some fish and poultry; little dairy products, red meat, processed meats, or sweets; and wine in moderation and consumed with meals.

Studies have shown that this type of diet is the most likely to protect people from heart problems. In studies where researchers have asked people about what they eat, people who eat a Mediterranean diet were less likely to have problems like heart attacks and strokes and less likely to die from them.

But these types of studies can only suggest a link between the Mediterranean diet and these problems - it can’t show cause and effect. That’s because people who choose to eat a Mediterranean diet may be healthier in other ways. They may not smoke, for example, or they may exercise more. So it’s hard to tell what is down to diet.

Cause and effect can be shown by a study that randomly divides people into different groups following different types of diet. There have been some of these studies looking at the Mediterranean diet for people with heart disease, but fewer of this type of study in people without previous heart or circulation problems.

This study included 7,447 people in Spain aged between 55 and 80 years old who hadn’t had heart disease in the past, but were at risk of heart disease because they had other health problems like type 2 diabetes, high blood pressure or high cholesterol, were overweight or had close family members who had had heart disease.

They were divided into three groups. One group followed a Mediterranean diet with approximately one litre of extra virgin olive oil a week. A second group followed a Mediterranean diet with a 30 gram serving of nuts a day. A third group, the comparison group, didn’t follow a specific diet but were given advice about how to reduce the amount of unhealthy fats in their diet. All three groups met with dietitians to get advice and training about their diet.

After an average of around five years, researchers worked out whether people who followed a Mediterranean diet were less likely to have a heart attack or stroke, or to die from heart problems, than people who didn’t.

What does the new study say?

People in either Mediterranean diet group were less likely to have a heart attack or a stroke, or to die from heart problems, than people who didn’t follow this type of diet.

Around 38 in 1,000 people who followed the Mediterranean diet with olive oil, and around 34 in 1,000 people who followed the Mediterranean diet with nuts, had a heart attack, or a stroke, or died from heart problems. This compares to around 44 in 1,000 people who didn’t follow a Mediterranean diet.

For every year they were in the study, around 3 in 1,000 people who followed the Mediterranean diet avoided having a heart attack, or a stroke, or dying from heart problems.

How reliable is the research?

This was generally a large, well-conducted, good-quality study. The researchers checked how well people were following their diets by using questionnaires and by testing their blood for substances contained in olive oil and in nuts. This helps to avoid the results being affected by people not accurately remembering or recording what they ate.

There were some differences between the groups, for example in how many people had type 2 diabetes, but the researchers took this into account in their calculations, as well as differences in things like age and sex that can affect people’s risk of heart attacks and strokes.

The most potentially important thing to note about the study was that people in the group who didn’t follow the Mediterranean diet originally only had one session with a dietitian, at the beginning of the study. After three years, the researchers felt this lack of support might have affected the results and so from then on, people in every group met with a dietitian every three months. It’s possible that this could have affected the results and made the benefits of the Mediterranean diet seem more favourable.

What does this mean for me?

If you’ve been told by your doctor that you are at risk of heart disease in the future, making changes such as adjusting your diet might help you. This study suggests the Mediterranean diet, especially one with lots of low fat olive oil and nuts, is a good option and is likely to reduce the chances of health problems affecting the heart or circulation.

Source:

Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. New England Journal of Medicine. Published online 25 February.

Feb 26, 2013