Tuesday December 11 2007
Fish, vegetables and olive oil
"A Mediterranean diet can help you live longer," reported The Guardian and other newspapers today. They said a Mediterranean diet was one high in vegetables (excluding potatoes), fruits, nuts, beans, grains and fish. It was also low in saturated fat, meat and dairy products and contained a moderate amount of alcohol.
The Guardian said: “Women who stuck most closely to the alternate Mediterranean diet had a 22% smaller chance of dying from any cause, a 14% smaller chance of dying from cancer and a 21% smaller chance of dying from heart disease. The findings for men followed a similar pattern.”
These stories are based on a study of almost 400,000 older Americans that found that the more people conformed to a “Mediterranean dietary pattern”, the less likely they were to die over the 10-year period of the study. This study provides us with more evidence that a healthy balanced diet is good for our health and that we’re more likely to live longer by following one.
Where did the story come from?
Dr Panagiota Mitrou, Arthur Schatzkin and colleagues from the National Cancer Institute, University of Minnesota, and the American Association of Retired Persons (AARP), and Lund University in Sweden carried out this research. The study was funded by the National Institutes of Health, the National Cancer Institute and the Division of Cancer Epidemiology and Genetics. The study was published in the peer-reviewed medical journal Archives of Internal Medicine.
What kind of scientific study was this?
This prospective cohort study, called the National Institutes of Health-AARP Diet and Health study, investigated the effects of a Mediterranean diet on mortality over a 10-year period.
The researchers enrolled more than 500,000 people aged 50 to 71 who were members of the AARP. They all completed a questionnaire about themselves, including any health-related problems they had. For this analysis, researchers excluded people who had a history of cancer, heart disease, stroke, end stage kidney disease, diabetes, emphysema or who reported a very high or very low energy intake in their diet. This left 380,296 people for the analysis.
Study participants answered a questionnaire about their diets (the Diet History Questionnaire), which gave information about what foods they ate, how much of these foods they ate, and how often they ate them. The results were adjusted to take into account the fact that people ate different amounts in total, and the results were checked by asking the participants to recall what they ate in two separate 24-hour periods.
The researchers rated how well people’s diets conformed to a Mediterranean dietary pattern on a nine-point scale (called the alternate Mediterranean diet score, or aMED), with a higher score indicating greater conformity to a Mediterranean diet.
People gained points for a pattern that included vegetables (not including potatoes), legumes, fruits, nuts, whole grains or fish consumption in the top 50% of consumption, and for having a monounsaturated fat to saturated fat consumption ratio in the top 50%. People also gained a point for consuming a specific amount of alcohol (5g to 25g a day).
People lost points for being in the bottom 50% of consumption of these foods or of the monounsaturated fat to saturated fat ratio, or being in the top 50% of consumption of red and processed meats.
Researchers followed the participants for 10 years and recorded the cause of death of the people that died using national databases. They then compared the death rate of people whose dietary pattern was more like a Mediterranean diet (score six to nine on aMED) with that of people with a less Mediterranean diet (score zero to three on aMED).
In their analyses, the researchers adjusted for factors that might affect results including: smoking, age, race, education, body mass index, physical activity and total dietary energy consumed.
What were the results of the study?
During the study, 27,799 people died (about 7%of all people enrolled). Overall, people whose diets were most like a Mediterranean diet were less likely to die during the 10-year follow up period than people whose diets were less like a Mediterranean diet. These results were independent of whether people had ever smoked.
Men who conformed to a Mediterranean diet had a 21% less risk of dying during the follow-up than those who conformed poorly to the Mediterranean diet. When death was broken down by cause, men who ate a Mediterranean diet were 22% less likely to die from heart disease and 17% less likely to die from cancer.
Women who conformed to a Mediterranean diet were 20% less likely to die during follow-up, 19% were less likely to die from heart disease and 12% wer less likely to die of cancer than those who did not.
What interpretations did the researchers draw from these results?
The researchers concluded that their study provided strong evidence that, in the US, people who follow a Mediterranean dietary pattern reduce their risk of death from all causes including stroke, heart disease and cancer.
What does the NHS Knowledge Service make of this study?
This was a large and well-conducted study, which does suggest that there are benefits in following a Mediterranean dietary pattern. There are a few points to bear in mind when interpreting this study:
- As the researchers assessed how well people conformed to a Mediterranean diet as a whole, it is not possible to identify from this analysis whether it is an individual part of this diet that is having the beneficial effect. It can only be said that the dietary pattern as a whole seems to be beneficial.
- As with all studies of this kind, it is possible that factors other than the one being studied are responsible for the results. For example, the researchers found that people who smoked were less likely to conform to a Mediterranean diet, and this could affect the results. The researchers considered smoking and other factors in their analyses, but may not have totally eliminated their influence. However, they note that the benefits of conforming to a Mediterranean diet were seen in people who had never smoked, increasing confidence that smoking is not entirely responsible for the results seen.
- People’s diets were assessed by questionnaire when they enrolled. Although the researchers tried to make sure people were recalling consumption correctly by repeating the questionnaire, people may still have had inaccurate recall of what they ate. In addition, people’s diets may have changed over the follow up period, which could affect results.
- This study only included relatively healthy people, who did not have a history of cancer or other chronic diseases, and more than 90% of whom were white. These results may therefore not be representative of the potential benefits of a Mediterranean diet in people from different ethnic backgrounds, or people who are less healthy.
Overall, this study provides us with more evidence that a pattern of eating that is high in vegetables, legumes, whole grains and fish, and low in saturated fats and red and processed meats, is good for our health.
Sir Muir Gray adds...
Pass the olive oil.