The PREDIMED (Prevention with a Mediterranean Diet) study was multicentre research trial carried out in Spain which investigated the effect of the Mediterranean diet on the primary prevention (prevention of the onset) of cardiovascular disease. The experiment, co-ordinated by the University of Navarra in a multicentre study with PREDIMED (Prevention with a Mediterranean Diet) and the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition (CIBERobn), took place between 2003 and 2009. The experiment involved 7,447 people who were either men aged 55-80 or women aged 60-80, and who were not suffering from a cardiovascular disease at the beginning of the study. These participants had type 2 diabetes or at least 3 of the following health problems:

• A tobacco addiction
• Hypertension
• High levels of LDL ('bad') cholesterol
• Low levels of HDL ('good') cholesterol
• Excess weight or obesity
• A family history of premature coronary diseases
• Each participant was allocated at random one of three diets:
• A Mediterranean diet supplemented with extra virgin olive oil.
• A Mediterranean diet supplemented with nuts.
• A control diet (participants were given advice on how to reduce their intake of all types of fat).

The typical Mediterranean diet is generally characterised by plenty of olive oil, fruit, nuts, vegetables and cereals; moderate consumption of fish and poultry and low consumption of dairy products, red meat, processed meat and cakes and desserts. It also includes moderate consumption of wine with meals. The participants received dietary advice every three months and attended educational group sessions. In addition, depending on the group that they belonged to, they received certain supplements:

• Extra virgin olive oil (approximately 1 litre per week).
• 30g of nuts per day (15g of walnuts, 7.5 of hazelnuts and 7.5g of almonds).
• The control group received advice on how to cut down on fat.

The PREDIMED study has become a benchmark in its field and in addition, it has allowed researchers to conduct a subanalysis of the effects of diet on other diseases. The study covered a period of 10 years and in 2013 its results were published with the following conclusion: ''Among people at a risk of developing cardiovascular diseases, a Mediterranean diet supplemented with extra virgin olive oil or nuts reduces the incidence of severe diseases of this type.'' The second phase of the PREDIMED study is in progress. This time, the effects of a low-calorie Mediterranean diet on obesity are being studied. The effects of cognitive behavioural therapy and the role of physical activity in helping to reduce weight are also being analysed, with the aim of determining whether in the long term cardiovascular problems and the incidence of cancer are reduced.