The Mediterranean diet, good for your health?
The Mediterranean diet consists of an abundance of whole-grain cereal products, colorful fruits and vegetables, and legumes, in particular.
Inscribed since 2013 on the UNESCO list of Intangible Cultural Heritage, the Mediterranean diet is attributed many virtues, including that of preventing heart disease. The Rumor Detector verified what is known about its effectiveness.
The origin of the rumor
As explained by the Montreal Heart Institute, which recommends a Mediterranean-type diet, it emphasizes whole-grain cereal products, colorful fruits and vegetables, legumes, soy and its derivatives, olive oil and canola oil, fish, nuts, flax and chia seeds, as well as home-cooked meals. This diet, rich in alpha linoleic acid, is inspired by the diet of the inhabitants of the Mediterranean basin in the 1950s and 1960s.
Indeed, this diet was first described in a book published in 1953 and dedicated to Crete. Its authors are researchers who have collected data on the difficult living conditions of the inhabitants of this Greek island, then considered an “underdeveloped region”. They observed that the Cretans consumed little meat and dairy products and that their diet consisted mainly of foods of plant origin (wild plants, herbs, fruits and vegetables) and virgin olive oil.
At the same time, the American physiologist Ancel Keys began a study in seven countries to compare the frequency of cardiovascular disease in different populations. He includes Crete, in particular because of its different diet from that of the countries of northern Europe. Result: cardiovascular diseases are rarer among Cretans. He concludes that diet would play an important role.
Promising results for cardiovascular health
A few subsequent studies confirmed these observations. For example, researchers in Lyon, France, in 1999 published the results of a study of patients who had survived a myocardial infarction. They recommended half of them to be careful with their diet and the other half to follow a Mediterranean-style diet. After studying participants for almost four years, they concluded that the Mediterranean diet reduced the risk of cardiac death and re-infarction by 70%.
More recently, a study of the same type in Spain, published in 2018, went in the same direction. Patients who were at high risk of cardiovascular disease and who were recommended the Mediterranean diet had about a 30% lower risk of serious cardiovascular events in the following five years, compared to those who were recommended consume less fat.
In 2017, Italian researchers reviewed 13 meta-analyses of observational studies, and 16 meta-analyses of randomized controlled trials, i.e. in which researchers intervene in the choice of diet . In all, these studies represented a total of nearly 13 million patients. The conclusion of the Italian researchers: the Mediterranean diet would be associated with a reduction in the risk of chronic diseases and mortality. It would also reduce weight, body mass index, waist circumference and cholesterol levels. In addition, it would reduce the risk of diabetes, promote better blood sugar control and reduce insulin resistance. Finally, the researchers observed a possible protective effect against certain cancers and neurodegenerative diseases. According to scientists, the diet would be beneficial because it would fight inflammation and the accumulation of fatty deposits on the inner lining of the arteries.
A few flats
According to what the non-profit collective Cochrane – which publishes systematic health reviews – wrote in 2019, the quality of studies on the Mediterranean diet is not yet sufficient to determine its effectiveness in preventing cardiovascular disease.
One of the problems comes from the very variable way of describing this type of diet. In a review of several meta-analyses published in 2018, German researchers listed more than 34 different definitions. For example, in the Lyon study, olive oil was replaced with canola-based margarine. The Cochrane collective has also chosen two fairly broad criteria to determine whether a study should be included in its analysis: the proposed diet has a higher content of monounsaturated fat than saturated fat and it is composed of a lot of vegetable products (fruits, vegetables, legumes).
Moreover, noted in 2014 the British doctor Richard Smith, it is difficult to assess whether a diet can prevent certain diseases. It is indeed complicated for a person to record all the foods consumed and to evaluate their nutritional content. In addition, a person's diet can vary greatly over their lifetime. Finally, research indicates that most patients have difficulty following a diet they are unfamiliar with.
Richard Smith also pointed out in his text, which appeared in the British Medical Journal, the role of certain food lobbies, such as the International Olive Council (formerly the International Olive Oil Council), which may have played an important role in the popularity of this diet, without regard to scientific arguments.
Studies on the Mediterranean diet tend to show that this type of diet could have beneficial effects on health, especially cardiovascular. But the variable quality of the studies and the difficulty in agreeing on the exact content of such a diet make it difficult to reach a consensus.