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A number of diets have received attention, but the strongest evidence for a beneficial health effect and decreased mortality after switching to a largely plant based diet comes from studies of Mediterranean diet, e.g. from the NIH-AARP Diet and Health Study.[24]
The Mediterranean diet often is cited as beneficial for being low in saturated fat and high in monounsaturated fat and dietary fiber. One of the main explanations is thought to be the health effects of olive oil included in the Mediterranean diet.
Research has shown that people who adopt a strict Mediterranean diet and take regular exercise, often find this helps keep their weight under control. Mediterranean-style meals packed with fruit, vegetables and grains can be quite filling, which reduces any desire to top up with extra calories.[25]
Dietary factors are only part of the reason for the health benefits enjoyed by certain Mediterranean cultures. Physically active lifestyle or labour is also beneficial.[26][27] Environment may also be involved. However, on the population level, i.e. for the population of a whole country or a region, the influence of genetics is rather minimal, because it was shown that the slowly changing habits of Mediterranean populations, from an active lifestyle and Mediterranean diet to a less physically active lifestyle and a diet influenced by the Western pattern diet, significantly increases risk of heart disease.[28][29][30] There is an inverse association between adherence to the Mediterranean diet and the incidence of fatal and non fatal heart disease in initially healthy middle aged adults in the Mediterranean region.[31]
A 2011 systematic review found that a Mediterranean diet appeared to be more effective than a low-fat diet in bringing about long-term changes to cardiovascular risk factors, such as lowering cholesterol level and blood pressure.[32]
The putative benefits of the Mediterranean diet for cardiovascular health are primarily correlative in nature; while they reflect a very real disparity in the geographic incidence of heart disease, identifying the causal determinant of this disparity has proven difficult. The most popular dietary candidate, olive oil, has been undermined by a body of experimental evidence that diets enriched in monounsaturated fats such as olive oil are not atheroprotective when compared to diets enriched in either polyunsaturated or even saturated fats.[33][34] A recently emerging alternative hypothesis to the Mediterranean diet is that differential exposure to solar ultraviolet radiation accounts for the disparity in cardiovascular health between residents of Mediterranean and more northerly countries. The proposed mechanism is solar UVB-induced synthesis of Vitamin D in the oils of the skin, which has been observed to reduce the incidence of coronary heart disease, and which rapidly diminishes with increasing latitude.[35] Interestingly, residents of the Mediterranean are also observed to have very low rates of skin cancer (which is widely believed to be caused by over-exposure to solar UV radiation); incidence of melanomas in the Mediterranean countries is lower than in Northern Europe and significantly lower than in other hot countries such as Australia.[36] It has been hypothesized that some components of the Mediterranean diet may provide protection against skin cancer.
A 2013 Cochrane review found limited evidence that a Mediterranean diet favorably affects cardiovascular risk factors.[37]
The global spread of the Mediterranean diet may be contributing to the marked increase of gluten-related disorders, such as coeliac disease and non-celiac gluten sensitivity, as it includes high levels of gluten.[38][39]