Published in the Canadian Medical Association Journal, the research looked at the long-term effects of a randomised controlled trial 'PREDIMED', which saw men and women aged 55–80 years old with a high risk of heart disease given either a Mediterranean diet supplemented with extra-virgin olive oil; a Mediterranean diet with nuts; or a control low-fat diet.
Around 64% (3,707) of the 5,801 participants had metabolic syndrome at the start of the study. After a mean follow-up period of 4.8 years, participants given the two Mediterranean diets decreased their central obesity levels and 958 participants (28.2%) no longer fell within the criteria for metabolic syndrome. The olive oil group were also more likely to have reduced their previously high fasting plasma levels.
Despite this, the Mediterranean diets did not appear to impact the number of new cases of metabolic syndrome or occurrence of its symptoms among the participants after a median period of 3.2 years and a maximum of seven years. The researchers said this went against the findings of some earlier studies.
"Mediterranean diets supplemented with olive oil or nuts were not associated with a reduced incidence of metabolic syndrome compared with a low-fat diet; however, both diets were associated with a significant rate of reversion of metabolic syndrome," the researchers said.
The nuts and bolts
Participants randomly assigned to the Mediterranean diet groups were given either extra virgin olive oil (about one litre a week) or mixed nuts (30 grams a day made up of 15 g walnuts, 7.5 g hazelnuts and 7.5 g almonds) at no personal cost. In the control group participants were given small non-food gifts.
To assure adherence to each diet, all three were offered written guidance and contact time in groups. The intervention groups were given information on typical Mediterranean foods, seasonal shopping lists, meal plans and recipes and were asked to complete a 13-point questionnaire during sessions. For the control group they were simply told to reduce intake of all types of fat from both animal and vegetable sources. At the beginning of the study this information was given in leaflet form, but this was then upped to match that given the Med groups with personalised advice, group sessions and a 9-point questionnaire.
The participants were not advised on physical activity in any of the groups and the researchers found that body weight and physical activity did not significantly differ across the three groups.
Dr Jordi Salas-Salvadó, one of the authors of the study, said: "Because there were no between-group differences in weight loss or energy expenditure, the change is likely attributable to the difference in dietary patterns."
Source: Canadian Medical Association Journal
Published online ahead of print, doi:10.1503/cmaj.140764
“Mediterranean diets and metabolic syndrome status in the PREDIMED randomized trial”
Authors: N. Babio, E. Toledo, R. Estruch, E. Ros, M. A. Martínez-González, O. Castañer, M. Bulló, D. Corella, F. Arós, E. Gómez-Gracia, V. Ruiz-Gutiérrez, M. Fiol, J. Lapetra, R. M. Lamuela-Raventos, L. Serra-Majem, X. Pintó, J. Basora, J. V. Sorlí and J. Salas-Salvadó