Why a Mediterranean Diet Is Better for Heart Health

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Health mavens have long believed that a Mediterranean diet — one rich in olive oil, seafood, and nuts — lowers one's risk for cardiovascular disease, but that belief was based solely on small-scale studies and anecdotal data . . . until now. Early in 2013, The New England Journal of Medicine published the results of a nearly five-year-long study, called PREDIMED (Prevención con Dieta Mediterránea), that assessed this diet's effect on cardiovascular disease, providing scientific data to back up the old claims.

What is PREDIMED?

The PREDIMED study was designed to focus on the health effects of a Mediterranean diet on people who were at high risk for cardiovascular disease. In 2003, with the help and cooperation of a large number of Spanish universities, government organizations, and research facilities, PREDIMED researchers selected 7,447 high-risk individuals between the ages of 55 and 80 who had not been diagnosed with a cardiovascular disease. A participant was considered high-risk if they had type 2 diabetes or had at least three of the following risk factors:

  • A family history of premature coronary heart disease

  • Hypertension (high blood pressure)

  • Overweight or obesity

  • Smoking

  • Elevated low-density lipoprotein (LDL) cholesterol levels

    LDLs are the "bad fats" that you find, among other places, in fried foods and mass-produced sweet snacks.

  • Low high-density lipoprotein (HDL) cholesterol levels

    HDLs are the "good fats" found in olive oil, seafood, and unsaturated fats.

Participants were randomly assigned to one of three groups and were educated in and asked to follow three different dietary plans:

  • A Mediterranean diet supplemented with extra-virgin olive oil (EVOO)

  • A Mediterranean diet supplemented with nuts

  • A low-fat diet (the control group)

The participants were then followed for nearly five years, and their dietary habits and medical conditions were monitored. After the study ended, the results were compared.

How is a Mediterranean diet different?

Participants in the study were given some dietary guidelines based on the group to which they were randomly assigned.

Those in the low-fat control group were encouraged to follow what many consider a "normal, healthy diet":

  • Three servings per day of low-fat dairy

  • Three servings per day of bread, potatoes, pasta, or rice

  • Three servings per day of fresh fruit

  • Two servings per day of vegetables

  • Three servings per week of lean fish and seafood

They were discouraged from consuming

  • Vegetable oils (including olive oil)

  • Commercial baked goods

  • Nuts

  • Fried snacks

  • Red meat and processed meat

  • Fatty fish and seafood canned in oil

  • Spread fats

  • Sofrito (a sauce made of onions and tomatoes simmered in olive oil)

Participants on a Mediterranean diet were given different dietary guidelines, as shown in the following table.

Dietary Guidelines for the Mediterranean Diet
Increase intake of Decrease intake of
Olive oil Soda
Nuts Commercial baked goods
Fresh fruit and vegetables Spread fats
Legumes Red meat
Fatty fish Processed meat
Sofrito
White meat

In the Mediterranean diet group, those supplementing their diet with extra-virgin olive oil were asked to take in at least 4 tablespoons of olive oil a day. Those supplementing their diet with nuts were asked to consume 30 g of nuts per day (15 g of walnuts, 7.5 g of hazelnuts, 7.5 g of almonds). Both Mediterranean diet groups were encouraged to drink one glass of wine (with a meal) each day.

[Credit: Photo ©iStockphoto.com/bit245]
Credit: Photo ©iStockphoto.com/bit245

What were the study's conclusions?

After nearly 5 years, the 7,447 participants had suffered 288 times from one of three "endpoint events": a myocardial infarction (heart attack), a stroke, or death from a cardiovascular cause. The data revealed that those who were at a high risk of cardiovascular disease lowered their risk by following a Mediterranean diet rather than simply a low-fat diet.

PREDIMED Research Results
Med. Diet + EVOO Med. Diet + Nuts Low-Fat Diet
(control)
Total
No. of participants 2,543 2,454 2,450 7,447
Total no. of events
(percent)
96
(3.8%)
83
(3.4%)
109
(4.4%)
288
(3.9%)
Stroke
(percent)
49
(1.9%)
32
(1.3%)
58
(2.4%)
139
(1.8%)
Myocardial infarction
(percent)
37
(1.5%)
31
(1.3%)
38
(1.6%)
106
(1.4%)
Death from cardiovascular cause
(percent)
26
(1.0%)
31
(1.3%)
30
(1.2%)
87
(1.2%)

Note: The total number of endpoint events is less than the sum of each suffered endpoint event because some participants experienced more than one event.

Analysis of the results showed a 30% reduction in the relative risk of cardiovascular disease among high-risk individuals who hadn't previously been diagnosed with a cardiovascular disorder. They also revealed a significant reduction specifically for stroke among those following a Mediterranean diet. These results led the researchers to conclude the following:

Among persons at high cardiovascular risk, a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced the incidence of major cardiovascular events, according to The New England Journal of Medicine.

What do these conclusions mean for the future? Doctors will now take a second look at the diets they put their heart patients on and consider other possibilities. A low-fat diet alone might not be enough. This data may even lead to changes in dietary recommendations for everyone.

And this study will almost certainly lead to a spate of short-lived diet schemes based on the Mediterranean diet.


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