Ancel and Margaret Keys, an American husband-and-wife team, first reported on the Mediterranean diet’s health benefits in 1975. Since then, the diet has become particularly well known for its effect on cardiovascular health. What is less well known is whether the diet has different benefits for men and women. Our latest study sheds some light on the matter.
We found that eating a Mediterranean diet may reduce the risk of stroke by more than one-fifth in women aged 40 or older, but it appears to have no significant impact on men’s risk of stroke. We also found that in both men and women at high risk of cardiovascular disease, those who followed a Mediterranean diet had a 13% reduced risk of stroke, although this reduction was largely driven by women.
In our analysis, the Mediterranean diet as a whole appears to be more strongly protective against the risk of stroke than the individual foods within it. When we analysed individual foods, there were few significant associations with stroke risk. The benefits appear to come from the additive effects of combining a diet high in fish, fruits, vegetables, nuts and beans, cereals and potatoes. A Mediterranean diet also has a lower intake of meat and dairy and a lower ratio of unsaturated to saturated fat.
Although studies have investigated whether the effect of the Mediterranean diet is important for preventing stroke, only two previous studies investigated the difference of the associations between men and women. We believe that this is the first study to investigate the relevance of the Mediterranean diet on people at different levels of cardiovascular disease risk.
Most earlier studies have been in trials of people at high risk of cardiovascular disease. Population studies (which is what our study was) have not investigated the risk of stroke in people according to their risk of cardiovascular disease.
The traditional Mediterranean diet developed in Greece – and the key components are well known: olive oil as the main source of fat, high intakes of fish, fruit, vegetables, nuts and legumes and low meat and dairy consumption with moderate alcohol consumption. But we know from our previous research that the foods that contribute to the Mediterranean diet vary, depending on whether one lives in a Mediterranean or a non-Mediterranean country, leading to differences in nutrient intake. These differences could affect one’s risk of disease. So disease risk in different countries could vary due to differences in the type of Mediterranean diet. This is why we wanted to investigate the risk of stroke in people in the UK.
Before our study, there was only one study in the UK that used a food frequency questionnaire and one other small study that used a diary method. Diary methods are considered to be more precise than food frequency questionnaires because they are an actual record of what a person ate for a given time rather than a recollection of diet at a particular point in time.
For our study, we looked at the food diaries of 23,232 people, aged 40 to 77, in Norfolk, UK, to find out if following a Mediterranean diet could prevent stroke of any type.
We measured the Mediterranean diet by calculating a score based on how close it was to a traditional Mediterranean diet. We also measured blood cholesterol and blood pressure and collected other important factors that affect stroke risk such as having diabetes and smoking. We took all this into account in our analysis. In the 17-year follow-up period, 2,009 people in our study had a stroke.
Women benefit the most
We found that women benefited the most from a Mediterranean diet. Their risk of stroke was reduced by 22%. This means that if 14 women per 10,000 people have a stroke that the risk would be reduced to 11 women per 10,000 – so, three lives saved in 10,000. There was no statistically significant reduction in stroke risk in men who adhered to a Mediterranean diet. Future research needs to investigate why men and women differ in response to the Mediterranean diet and if this is due to the differences in risk factors that affect women only, or whether women respond differently for risk factors such as blood pressure and diabetes. For this, we need randomised controlled trials.
One of the limitations of our study was that we measured diet at the start of the study and so cannot exclude the possibility that people’s diets changed during the study period.
We were also unable to look at racial diversity as the study was done in Norfolk, UK, where there is insufficient diversity to understand the relationship between diet and stroke for a non-white population. This would also be important to research in the future as people who are black and of African or Caribbean origin have a higher risk of stroke than other people in the UK.
Ailsa Welch, Professor of Nutritional Epidemiology, University of East Anglia.
This article first appeared on The Conversation.
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