Data on the Diet

If you’re like me, you want to see the science behind the claims. In this article I’ve written summaries of the findings of a few big studies on the Mediterranean diet. Included are links to the publication so you can see the data for yourself. While the interventions for all of these studies were some version of the Mediterranean diet, the people who participated in the studies had different risk factors. I have divided the studies up according those risk factors.

All of the studies I included here are randomized controlled trials (RCT). A RCT identifies participants who meet the criteria of the study. The participants are randomly assigned to an intervention group or to a control group. These are true experiments and have the most reliable outcomes. RCT findings are the very definition of strong evidence.

Strong evidence does not mean truth or fact. All studies have weaknesses. For example, I’m completely baffled by the control groups in these large, highly-touted studies. All of them had control groups on a low-fat diet. Missing was a control group whose members ate regional foods in an unmodified diet.

In the findings of RCTs (and other studies for that matter), you will see terms such as “associated with” or “related to”, “risk reduction” or “incidence of”; not “proof”, “truth”, or “cause and effect”.

People with high risk of cardiovascular disease

In recent years, the PREDIMED trial has many publications in scientific journals. PREDIMED was a multi-year trial conducted in Spain including 7447 individuals at high risk of cardiovascular disease who were randomly assigned to one of three diets:

• An energy-unrestricted (calories/amount of food not limited) Mediterranean diet with added extra virgin olive oil (Med + Olive Oil)

• An energy-unrestricted Mediterranean diet with added nuts (Med + Nuts)

• A low fat diet control group

The study was published in 2013 and reported a reduction in the incidence of major cardiovascular events (heart attack, stroke, or death from cardiovascular disease). The risk reduction was 30% in the Med + Olive Oil group, and 28% in the Med + Nuts group.

An energy-unrestricted Mediterranean diet, supplemented with extra-virgin olive oil or nuts, resulted in a substantial reduction in the risk of major cardiovascular events among high-risk persons. The results support the benefits of the Mediterranean diet for the primary prevention of cardiovascular disease.

Sub-studies from the PREDIMED found:

• reversal of metabolic syndrome by 13.7% in the Med + Nuts group

• reduction in oxidative stress biomarkers in both Mediterranean diet groups

• reduction in risk of developing type 2 diabetes in both Mediterranean diet groups

• showed beneficial effects on several cardiovascular risk factors in the Mediterranean diet groups

• showed risk of death was significantly less in the Med + Nuts group

People with history of heart attack

The Lyon Diet Heart Study enrolled 605 middle-aged men and women with a history of having suffered one heart attack. The study enrollees were assigned to one of two diet groups:

• Mediterranean diet supplemented with high omega-3 margarine

• prudent Western-type diet for control group

Results of the study after 4 years suggest a protective effect of the Mediterranean diet, significantly reducing the risk of having a second heart attack or dying from heart disease.

People with metabolic syndrome

This RCT conducted in Naples, Italy enrolled 180 men and women diagnosed with metabolic syndrome. Enrollees had stable weight and were sedentary. They were randomly assigned to one of two groups:

• Mediterranean diet

• low-fat diet

After 2 years, 30 out of 91 patients in the Mediterranean diet group and 73 out of 91 patients in the low fat diet group were classified as still having metabolic syndrome. The level of physical activity increased in both groups. Weight decreased by 8.8 pounds in the Mediterranean diet group compared to 2.6 pounds in the low-fat diet group. Endothelial function, inflammatory markers, and insulin resistance improved significantly in the Mediterranean diet group.

People with high bodyweight

The PREDIMED trial did not limit calories or fat intake for the participants assigned to the Mediterranean diet groups. After 4.8 years, the participants in all three groups had reduced their bodyweight by a small amount while also increasing their waist circumference. The participants in both Mediterranean groups lost more weight and had smaller increase in waist circumference than those in the low fat diet group. Overall, the changes in weight and waist circumference were very small and could be interpreted as weight stability.