Heart disease is a major problem around the world.
However, research shows that the incidence of heart disease seems to be lower among people living in Italy, Greece, and other countries around the Mediterranean, compared with those living in the United States. Studies suggest that diet may play a role.
People around the Mediterranean have traditionally followed a diet that’s rich in plant-based foods, including fruits, vegetables, whole grains, breads, legumes, potatoes, nuts, and seeds.
The main dietary fat is extra virgin olive oil, and people also consume moderate amounts of red wine, fish, poultry, dairy, and eggs. Meanwhile, red meat plays only a small part.
This eating pattern has started to become popular around the world as a means to improve health and prevent disease.
Several randomized controlled trials, which are reliable and effective methods of research, have looked at the possible benefits of this diet.
This article looks at 5 long-term controlled trials on the Mediterranean diet. All of them appear in respected, peer-reviewed journals.
Most people who joined these studies had health problems, including diabetes, metabolic syndrome, or a high risk of heart disease.
Most of the studies looked at common health markers, such as weight, heart disease risk factors, and markers of diabetes. Some larger studies also looked at rates of heart attacks and death.
1. The PREDIMED Study
This large study involved 7,447 individuals with a high risk of heart disease.
For almost 5 years, the participants followed one of three different diets:
- a Mediterranean diet with added extra virgin olive oil (Med + Olive Oil)
- a Mediterranean diet with added nuts (Med + Nuts)
- a low fat diet control group
None of the diets involved reducing calories or increasing physical activity.
Many researchers have used data collected during PREDIMED to investigate its effect. The studies looked at the diet’s effect on different risk factors and end points.
Here are 6 papers (1.1 to 1.6) from the PREDIMED study.
1.1 Estruch R, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra Virgin Olive Oil or Nuts. The New England Journal of Medicine, 2018.
Details. In this study, 7,447 individuals with a high risk of heart disease followed either a Mediterranean diet with added olive oil, a Mediterranean diet with added nuts, or a low fat control group. The study lasted for 4.8 years.
The main focus was the diet’s potential effect on heart attack, stroke, and death from cardiovascular causes.
Results. The risk of combined heart attack, stroke, and death from heart disease was lower by 31% in the Med + Olive Oil group and 28% in the Med + Nuts group.
- There were no statistically significant differences in heart attacks or stroke between the diets.
- Dropout rates were twice as high in the control group (11.3%), compared with the Mediterranean diet groups (4.9%).
- People with high blood pressure, lipid problems, or obesity responded better to the Mediterranean diet than the control diet.
- There was no statistically significant difference in total mortality, which is the overall risk of death from all causes.
Conclusion. A Mediterranean diet with either olive oil or nuts may reduce the combined risk of stroke, heart attack, and death from heart disease.
1.2 Salas-Salvado J, et al. Effect of a Mediterranean Diet Supplemented With Nuts on Metabolic Syndrome Status. JAMA Internal Medicine, 2008.
Details. Researchers analyzed data from 1,224 individuals in the PREDIMED study after following the diet for 1 year. They looked at whether the diet helped reverse metabolic syndrome.
Results. The prevalence of metabolic syndrome decreased by 6.7% in the Med + Olive Oil group and 13.7% in the Med + Nuts group. The results were statistically significant only for the Med + Nuts group.
Conclusion. A Mediterranean diet supplemented with nuts may help reverse metabolic syndrome.
1.3 Montserrat F, et al.
Details. Scientists assessed 372 individuals with a high risk of heart disease after following a diet in the PREDIMED study for 3 months. They looked at changes in oxidative stress markers, such as oxidized LDL (bad) cholesterol.
Results. Levels of oxidized LDL (bad) cholesterol decreased in both Mediterranean diet groups but did not reach statistical significance in the low fat control group.
Conclusion. People who followed the Mediterranean diet experienced reductions in oxidized LDL (bad) cholesterol, along with improvements in several other heart disease risk factors.
1.4 Salas-Salvado J, et al.
Details. Researchers assessed 418 people without diabetes who participated in the PREDIMED study for 4 years. They looked at their risk of developing type 2 diabetes.
Results. In the two Mediterranean diet groups, 10% and 11% of people developed diabetes, compared with 17.9% in the low fat control group. The Mediterranean diet appeared to reduce the risk of developing type 2 diabetes by 52%.
Conclusion. A Mediterranean diet without calorie restriction appears to prevent the development of type 2 diabetes.
1.5 Estruch R, et al.
Details. Scientists analyzed data for 772 participants in the PREDIMED study with regards to cardiovascular risk factors. They had been following the diet for 3 months.
Results. Those on a Mediterranean diet saw improvements in various cardiovascular risk factors. These included blood sugar levels, blood pressure, the ratio of total to HDL (good) cholesterol, and levels of C-reactive protein (CRP), a marker of inflammation and various diseases.
Some more details:
- Blood sugar: fell by 0.30–0.39 mmol/L in the Mediterranean diet groups
- Systolic blood pressure: fell by 5.9 mmHG and 7.1 mmHG in the two Mediterranean diet groups
- Total to HDL (good) cholesterol ratio: fell by 0.38 and 0.26 in the two Mediterranean diet groups, compared with the low fat group
- C-reactive protein: fell by 0.54 mg/L in the Med + Olive Oil group, but did not change in the other groups
Conclusion. Compared with a low fat diet, a Mediterranean diet appears to improve various risk factors for heart disease.
1.6 Ferre GM, et al.
Details. Scientists evaluated 7,216 participants in the PREDIMED study after 5 years.
Results. After 5 years, a total of 323 people had died, with 81 deaths from heart disease and 130 deaths from cancer. Those who consumed nuts appeared to have a 16–63% lower risk of death during the study period.
Conclusion. Consuming nuts as part of a Mediterranean diet may significantly reduce the risk of death.
2. De Lorgeril M, et al.
Details. This study enrolled 605 middle-aged males and females who had had a heart attack.
For 4 years, they consumed either a Mediterranean-type diet (supplemented with an omega-3-rich margarine) or Western-type diet.
Results. After 4 years, those who followed the Mediterranean diet were 72% less likely to have experienced a heart attack or died from heart disease.
Conclusion. A Mediterranean diet with omega-3 supplements may help prevent a repeat heart attack in people who have had a heart attack.
3. Esposito K, et al. Effect of a Mediterranean-Style Diet on Endothelial Dysfunction and Markers of Vascular Inflammation in the Metabolic Syndrome. The Journal of the American Medical Association, 2004.
Details. In this study, 180 people with metabolic syndrome followed either a Mediterranean diet or low fat diet for 2.5 years.
Results. At the end of the study, 44% of patients in the Mediterranean diet group still had metabolic syndrome, compared with 86% in the control group. The Mediterranean diet group also showed improvements in other risk factors.
Some more details:
- Weight loss. Body weight decreased by 8.8 pounds (4 kg) in the Mediterranean diet group, compared with 2.6 pounds (1.2 kg) in the low fat control group.
- Endothelial function score. This improved in the Mediterranean diet group but remained stable in the low fat control group.
- Other markers. Inflammatory markers (hs-CRP, IL-6, IL-7, and IL-18) and insulin resistance decreased significantly in the Mediterranean diet group.
Conclusion. A Mediterranean diet appears to help reduce metabolic syndrome and other cardiovascular risk factors.
4. Shai I, et al. Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet. The New England Journal of Medicine, 2008.
Details. In this study, 322 people with obesity followed either a calorie-restricted low fat diet, calorie-restricted Mediterranean diet, or an unrestricted low carb diet.
Results. The low fat group lost 6.4 pounds (2.9 kg), the low carb group lost 10.3 pounds (4.7 kg), and the Mediterranean diet group lost 9.7 pounds (4.4 kg).
In those with diabetes, blood glucose and insulin levels improved on the Mediterranean diet, compared with the low fat diet.
Conclusion. A Mediterranean diet may be more effective than a low fat diet for weight loss and managing diabetes.
5. Esposito K, et al.
Details. In this study, 215 people with overweight who had recently received a diagnosis of type 2 diabetes followed either a low carb Mediterranean diet or a low fat diet for 4 years.
Results. After 4 years, 44% of the Mediterranean diet group and 70% of the low fat diet group needed treatment with medication.
The Mediterranean diet group had more favorable changes in glycemic control and heart disease risk factors.
Conclusion. A low carb Mediterranean diet may delay or prevent the need for drug therapy in people who are newly diagnosed with type 2 diabetes.
Two of the studies — the PREDIMED study and the Lyon Diet Heart study — involved enough people and lasted long enough to obtain results about mortality, or the risk of death during the study period (1.1,
To compare them more easily, this article combines the two types of Mediterranean diets in the PREDIMED study into one.
In the Lyon Diet Heart Study, the Mediterranean diet group was 45% less likely to die over the 4-year period than those in the low fat group. Some experts have called this study the most successful diet intervention study in history.
The Mediterranean diet group in the PREDIMED study was 9.4% less likely to die, compared with the control group, but the difference was not statistically significant.
The risk of dying from heart disease was 16% lower (not statistically significant) among those in the PREDIMED study and 70% lower in the Lyon Diet Heart Study.
The risk of stroke was 39% lower in the PREDIMED study, on average (31% with olive oil and 47% with nuts), which was statistically significant. In the Lyon Diet Heart Study, 4 people in the low fat group had a stroke, compared with none in the Mediterranean diet group.
The Mediterranean diet is not primarily a weight loss diet, but it is a healthy diet that can help prevent heart disease and early death.
However, people may lose weight on the Mediterranean diet.
In every study the Mediterranean group lost more weight than the low fat group, but it was only statistically significant in one study (3).
Several studies have shown that the Mediterranean diet can benefit people with metabolic syndrome and type 2 diabetes.
- The PREDIMED study showed that a Mediterranean diet with nuts helped 13.7% of people with metabolic syndrome reverse their condition (1.2).
- Another paper from the same study showed that the Mediterranean diet reduced the risk of developing type 2 diabetes by 52% (
- Esposito, 2004 showed that the diet helped reduce insulin resistance, one feature of metabolic syndrome and type 2 diabetes (3).
- The Shai study showed that the Mediterranean diet improved blood glucose and insulin levels, compared with the low fat diet (4).
- Esposito, 2009 showed that the diet could delay or prevent the need for medication in people newly diagnosed with type 2 diabetes.
The Mediterranean diet appears to be an effective option for people with type 2 diabetes.
Number of people who dropped out of the studies
In all the investigations, some people dropped out of the research.
However, there are no clear patterns in the dropout rates between the Mediterranean and low fat diets.