Mediterranean Diet Enriched With Walnuts Also Protects Against Oxidative Damage

03/07/07 - Findings from a new study show that a decrease in the oxidative damage to LDL cholesterol is one of the protective mechanisms by which the Mediterranean diet exerts a protective effect on coronary heart disease development.

- The first results of the PREDIMED study reported an improvement in markers of cardiovascular disease that, in the long term, could translate into a 50% reduction in the risk of suffering a heart attack.

- PREDIMED is a long-term multicenter trial -supported by the Spanish Health Ministry- designed to assess the effects of a Mediterranean-style diet on the primary prevention of cardiovascular disease. 17 groups of Spanish researchers in 200 health centres in Spain and 9000 patients at high risk of cardiovascular disease participate in the study.

Findings from a new study show that a decrease in the oxidative damage to LDL cholesterol is one of the protective mechanisms by which the Mediterranean diet exerts a protective effect on coronary heart disease development. Data from this study provide further evidence to recommend the Mediterranean diet as a useful tool against atherosclerosis development, particularly in individuals at high risk of developing coronary disease.

The results of this substudy, part of the large Prevencion con Dieta Mediterranea (PREDIMED) study, are published in the June 11, 2007 issue of the leading medical journal Archives of Internal Medicine.

As the study reports, the investigators designed a large-scale feeding trial in a population at hight risk for coronary heart disease to assess the effects on cardiovascular outcomes of 2 Mediterranean diets, one supplemented with mixed nuts, mainly walnuts and the other with virgin olive oil -the main fat component of the Mediterranean diet. Boths diets were compared with a low-fat diet. The daily dose of mixed nuts included 15 g walnuts, 7.5 g hazelnuts, and 7.5 g almonds. Walnuts have a favorable fatty-acid profile and are a rich source of nutrients and other bioactive compounds, such as fiber, phytosterols, folic acid, and antioxidants, which might beneficially influence against the risk factors for heart diseases.

Individuals who improved their diet toward a Mediterranean diet pattern had significant reductions in their LDL oxidation compared with individuals assigned to a low-fat diet. Current evidence implicates oxidative damage as part of the pathophysiological changes occurring in various diseases, such as coronary heart disease, cancer, and neurodegenerative diseases, as well as aging, but as yet there are no randomized controlled intervention studies assessing the efficacy of the Mediterranean diet on in vivo lipoprotein oxidation.

"We also know that the Mediterranean diet is rich in fruits and vegetables and consequently rich in antioxidants, and a lot of people simply figured that it would be beneficial. But nobody has tested the antioxidant effects of this dietary pattern in a randomized trial. This is one of the reasons we started the study." says the general coordinator of the PREDIMED, Ramon Estruch, M.D., from the Service of Internal Medicine at Hospital Clinic, Barcelona.

Reduction in the risk of heart disease

The PREDIMED study, a long-term multicenter randomized controlled clinical trial designed to assess the effects of the Mediterranean diet on the primary prevention of cardiovascular disease, allowed investigators to test the hypothesis that oxidized LDL plays a major role in atherosclerosis and cardiovascular disease. An estimated 9000 high-risk participants, more than 6000 already recruited, will be assigned to three interventions: Mediterranean diet with virgin olive oil, Mediterranean diet with mixed nuts, or low-fat diet. The main outcome is an aggregate of cardiovascular events, including cardiovascular death, nonfatal MI, or nonfatal stroke; the study is expected to be completed in late 2010.

The first results of the PREDIMED study reported that the Mediterranean diet, supplemented with oil olive or nuts, basically walnuts, reduced arterial pressure, blood lipids, fasting blood glucose, and inflammation, thus favourably influencing all measured risk factors for heart disease (Annals of Internal Medicine, 2006). Given these results, Dr Estruch confirms "It's easy to foresee that the participants who follow the Mediterranean diet supplemented with olive oil or with nuts will show in the long run a 50% reduction in the incidence of cardiovascular complications."

"After the 3-month intervention period, the two groups following the Mediterranean diet were compared with the low fat diet group and showed lower blood pressure and decreased blood glucose levels, cholesterol, triglycerides and inflammation markers. They also had increased HDL cholesterol levels (good cholesterol)," as reported by Dr Estruch.

Emilio Ros, M.D., Head of the Lipid Clinic at Hospital Clinic, Barcelona, and researcher for PREDIMED, gives the reassurance that an important part of the benefits obtained by the group on the Mediterranean diet supplemented with nuts "Was probably due to the high levels of strong antioxidants found in walnuts". The study also highlighted that although the two Mediterranean diets had beneficial effects on blood lipids, triglycerides were only reduced in this group.

Additionally, "There were no increases in body weight even though the participants were consuming increased amounts of fatty foods (olive oil and nuts), probably because these foods contain good fats (unsaturated fats)," Dr. Ros reported.