Win Your Heart with the Mediterranean Diet
Rich in minimally processed plant-based food and monounsaturated fat from olive oil, but low to moderate in animal products, the Mediterranean diet (MedDiet), one of the most well studied dietary patterns in scientific literature, has been identified as one of the healthiest dietary patterns for prevention of cardiovascular diseases (CVDs)1-3. More established mechanisms underlying the beneficial effects of the MedDiet include protection against oxidative stress, inflammation and platelet aggregation, and improvements in lipid profiles, insulin sensitivity and endothelial function2,4,5. These effects are likely to be attributable to healthy nutrients such as monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs), bioactive compounds exerting antioxidant properties, such as polyphenols, and fibre2,4.
Defining the Mediterranean Diet (MedDiet)
Although cardiovascular diseases (CVDs) are largely preventable by managing modifiable risk factors, they are a leading cause of mortality in the world, accounting for 31% of all global deaths in 20153. Promoting healthy lifestyles, therefore, should be an important strategy to reduce CVD burden, and healthy eating habits have long been considered a crucial component of a heart-friendly lifestyle3,6. In that regard, the MedDiet, which is characterised by high intakes of vegetables, fruit, nuts, legumes and whole grains; moderate intakes of fish, white meat and low-fat dairy products; low intakes of red meat; a preference for olive oil and moderate wine consumption with meals, has been identified as one of the healthiest dietary patterns for CVD prevention (Figure 1)3,6.
Figure 1. The MedDiet pyramid1
The MedDiet is the generic term referring to the traditional dietary patterns of people living in the countries along the coast of Mediterranean Sea7. It was first defined by Ancel Keys as a diet low in saturated fat and high in vegetable oils in the 1960s. The pioneer epidemiological study supporting the MedDiet for cardiovascular health was the Seven Countries Study, an ecological, international investigation of diet and CVDs in nearly 13,000 men in 7 countries (Greece, Italy, Japan, Finland, the former Yugoslavia, the Netherlands and the United States)1,8. In this study, the MedDiet was found associated with a reduced risk of coronary heart disease (CHD) in people from southern Europe compared to those from northern Europe and the United States after 25 years of follow-up, highlighting the importance of this dietary pattern2,9. Since then, it has been extensively studied in nutritional epidemiology1.
The Cardiovascular Benefits of Key Nutrients in the MedDiet
In terms of nutrients, the MedDiet is low in saturated fatty acids but rich in monounsaturated fatty acids (MUFAs), especially oleic acid from olive oil. Olive oil is the principal source of the fat in the MedDiet and have a role in CVD prevention2,7,10. A large meta-analysis of 32 prospective observational studies has shown that the upper tertile of olive oil consumption is associated with a 20%-40% reduction in the risks of stroke and CHD, when compared with the lower tertile4. In addition to MUFAs, polyunsaturated fatty acids (PUFAs) are found in the MedDiet7. Nuts, another component of the MedDiet, are a rich source of not only MUFAs but also PUFAs, such as linoleic and linolenic acids4. In dose-response meta-analyses of prospective observational studies, nut consumption has been associated with lower risks of all-cause mortality, CHD, hypertension, and adiposity4.
The PREDIMED (PREvención con DIeta MEDiterránea) study, which is a long-term prospective multicentre double-blind randomised controlled trial comparing the MedDiet supplemented with extra-virgin olive oil or nuts with a relatively low-fat diet for the primary prevention of CVD in a Spanish population, is a landmark study and it remains the largest dietary intervention trial to date to assess the effects of the MedDiet on CVD prevention. The trial demonstrated that CVD could be reduced by approximately 30% by an increased intake of either olive oil, especially extra-virgin olive oil, or nuts. The findings of the PREDIMED study not only confirmed the beneficial role of the MedDiet, as suggested in previous epidemiological and prospective cohort studies, but also led to a paradigm shift in nutrition recommendations for CVD prevention1,2,10,11.
One of the most important components of the MedDiet that is rich in unsaturated fatty acids (UFAs) is fish. A vast array of studies have demonstrated the beneficial effects of fish consumption on CVD, and it is believed that the beneficial effects are attributed to the high level of omega-3 long-chain PUFAs such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)4,7.
Furthermore, the MedDiet recommends increased consumption of fruits and vegetables. Fruits, vegetables, whole grains and legumes are good sources of dietary fibre. A multitude of studies have revealed that a diet high in fibre is inversely associated with the risk of CVDs7.
The Effects of Polyphenols in the MedDiet on CVD Prevention
Increased dietary antioxidant intake has been observed associated with lower incidences of heart failure, stroke and CHD11. The traditional MedDiet is rich in antioxidants such as vitamins (β-carotene, vitamin C and vitamin E), natural folate, carotenoids, the mineral selenium, as well as polyphenols2,4,11. Polyphenols are a large and heterogeneous group of phytochemicals containing phenol rings, which are divided into flavonoids, phenolic acids, stilbenes and lignans, and particularly abundant in fruits, vegetables, whole grains, legumes, as well as in olive oil and red wine. More than 8,000 different polyphenols have been identified so far, and there is growing evidence that long-term intake of polyphenols has a positive effect on the incidence of CVDs2.
Subgroup analysis of the PREDIMED study revealed that higher polyphenol intake was associated with lower incidences of the primary outcome (composite of acute myocardial infarction, stroke, or death from cardiovascular causes), overall mortality, blood pressure, inflammatory biomarkers, new-onset type 2 diabetes mellitus, and obesity. However, it should be noted that some foods rich in polyphenols are also rich in UFA, such as olive oil, making it very difficult to differentiate the beneficial effects of one individual component from another. It is fully possible that the beneficial effect of polyphenols is synergistic with that of UFAs11. In fact, most of the health benefits provided by the MedDiet are due to the effects of biological interactions between different components rather than the effect of a single component7.
Pharmacological Mechanisms Underlying the Health Benefits of MedDiet
The exact mechanisms by which the traditional MedDiet exerts its beneficial effects in lowering the risk of developing CVDs remain to be elucidated. However, more established mechanisms provided by bioactive compounds of ingredients of the MedDiet include (1) reduction of levels of blood lipids, such as low-density lipoprotein (LDL) cholesterol and triglycerides, with PUFAs, phytosterols and water-soluble dietary fibres, (2) protection against oxidative stress and inflammation by reducing circulating oxidised LDL and inflammatory markers with antioxidative vitamins, polyphenols and omega-3 long-chain PUFAs, (3) improvement in insulin sensitivity by promoting better glycaemic control with polyphenols and fibres, (4) enhancement of endothelial function in terms of flow-mediated dilatation by increasing the local bioavailability of vasodilators, such as nitric oxide (NO), with polyphenols and omega-3 long-chain PUFAs, and (5) protection against platelet aggregation and coagulation by polyphenols (Figure 2)2,4,5.
Figure 2. The relationship between the MedDiet and CVDs4,11. CVD: cardiovascular disease. UFA: unsaturated fatty acid
Adherence to the MedDiet
A vast body of observational evidence has demonstrated adherence to the MedDiet is inversely associated with risks of all-cause mortality, CVDs, CHD, stroke and heart failure4. Despite its well-known health benefits and protective role in CVD prevention, a low adherence rate to the MedDiet has been documented12. A scoring system for adherence to the MedDiet has been proposed and would help people to recognise the importance of adherence to the diet8.
References
1. Martínez-González MA, et al. Circ Res 2019;124(5):779-798. 2. Ditano-Vázquez P, et al. Nutrients 2019;11(11): 2833. 3. Becerra-Tomás N, et al. Crit Rev Food Sci Nutr 2000;60(7):1207-1227. 4. Schwingshackl , et al. Br J Pharmacol 2020;177(6):1241-1257. 5. Tosti V, et al. J Gerontol A Biol Sci Med Sci 2018;73(3):318-326. 6. Amato M, et al. Nutr Metab Cardiovasc Dis 2020;30(8):1315-1321. 7. Asbaghi O, et al. Clin Nutr ESPEN 2020;37:148-156. 8. Rishor-Olney CR and Hinson MR. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan 2020 May 21. 9. Davis C, et al. Nutrients 2015;7(11):9139-9153. 10. Rosato V, et al. Eur J Nutr. 2019;58(1):173-191. 11. Billingsley HE and Carbone S. Nutr Diabetes 2018;8(1):13. 12. Raparelli V, et al. Nutrients 2020;12(3):759.
