The influence of Mediterranean diet in epidemiology

The influence of Mediterranean diet in epidemiology is a research of Tammy YN Tong and Nita G Forouhi.

Tammy Tong is undertaking her doctoral studies (PhD) at the MRC Epidemiology Unit in Cambridge, UK. Her work is focused on assessing the applicability of the Mediterranean diet in the UK context, and in examining etiological associations of the diet with cardio-metabolic disorders and Nita Forouhi is the Group Leader of the nutritional epidemiology program at the MRC Epidemiology Unit in Cambridge, UK. Trained in Medicine, Epidemiology and Public Health, Nita is interested in etiology, prevention and between-population differences.

Mediterranean countries are historically among the healthiest countries in the world, recording relatively low rates of cardiovascular diseases and cancer as well as greater longevity. This ecological observation led to the idea of a healthy Mediterranean diet, based on traditional diets of regions such as Crete, other parts of Greece and Southern Italy. Offering a potential solution to improve health and well-being through reduction in chronic disease incidence and mortality, the ‘Mediterranean diet’ has been studied for its effects on a range of conditions in countries not limited to the original Mediterranean region. Consistent with the findings of the landmark Lyon Diet Heart Study and the five-year PREDIMED trial, a number of long-term observational studies supported protective roles of the Mediterranean diet against non communicable diseases. The diet is also received favorably by the general population and government agencies alike, being rated joint third best diet overall by the US News & World Report, as well as being recommended by the UK National Health Service as a healthy meal choice. A further ‘feather in the cap’ of the Mediterranean diet is its recognition by UNESCO as an intangible cultural heritage of several Mediterranean countries [46].

To improve the evidence for the health benefits of the Mediterranean diet, more systematic and quantitative approaches are needed in research practice. To date, applicability of the Mediterranean diet to non-Mediterranean countries has not been established. The premier study in Greece by Trichopoulou evaluated eight dietary factors as components of the Mediterranean diet: vegetables, legumes, fruits and nuts, grains, meats, dairy, alcohol, as well as dietary fats, with fish added later on as a ninth component. However, while consumption of these factors provides a good approximation to a Mediterranean type diet under certain circumstances, it has several shortcomings. One problem is that the selection and use of the dietary information is too specific to the local populations studied. Therefore, when examining benefits of the Mediterranean diet in different populations, the patterns of consumption of key dietary components should be examined first in order to make appropriate adjustments.

Considering many advances in dietary research in the past decade, modifications to existing methods of assessing adherence to the Mediterranean diet are also warranted. This is particularly so since most studies have not evaluated the health benefits of adherence to the Mediterranean diet that was originally characterized in the Mediterranean region. For example, when assessing the Mediterranean diet, it still remains unclear as to whether, for alcohol intake, any distinction should be made between red wine and other types of alcohol, even though wine is the form of alcohol traditionally consumed in Mediterranean countries. While some epidemiological studies have reported potential health benefits of moderate wine consumption, the extent of these health benefits seems to be less apparent for other alcoholic beverages. However, only a few studies on the Mediterranean diet recognized wine as a standalone component instead of total alcohol. Future observational studies should take into account this differentiation, and ideally incorporate wine only as an element of the Mediterranean diet when assessing adherence to this dietary pattern. It will be of particular interest to examine differences in association with disease risk when wine alone versus total alcohol intake is included.

Moreover, high intake of dairy products is considered as adverse in the landmark publications on the Mediterranean diet and health. However, recent epidemiological evidence suggests lower cardiometabolic risk associated with consumption of dairy products, in particular fermented dairy products. Importantly, moderate amounts of fermented dairy products are also traditionally consumed in Mediterranean countries. Similarly, grains and meat products are of interest, in regards to whether whole grains and refined grains, or unprocessed red meats, processed meats, and poultry should be distinguished.

Existing studies of the Mediterranean diet have used varying definitions of the diet and found associations of adherence to the diet with different health outcomes. However, none of them has fully examined the traditional Mediterranean diet, reflecting the difficulty of attempting to use a simple definition to describe dietary behavior which is inherently complex. Future research should, therefore, aim to amalgamate existing definitions of the Mediterranean diet with up-to-date scientific evidence of health outcomes associated with individual components. Furthermore, the Mediterranean diet is essentially part of a lifestyle, requiring the simultaneous consideration of other non-dietary behavioral factors when assessing its effects. What the Mediterranean diet, therefore, means in the context of some countries with distinct cultural diets and lifestyles, such as for instance in China, India, and parts of Africa, needs further research and thought, despite the fair amount of evidence among the Western and, particularly, Mediterranean countries.

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