Sound Science: The Mediterranean Diet and Heart Health

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Heart disease affects many people in the U.S., with almost half of Americans having at least one of three risk factors (high blood pressure, high cholesterol, smoking) for heart disease. A 2013 study published in the New England Journal of Medicine examined if following a Mediterranean-style eating pattern would impact heart health. When the study was released, it generated quite a bit of attention for a variety of reasons and with the recent 2015-2020 Dietary Guidelines referencing a Mediterranean eating style, this dietary pattern remains top of mind for many as a healthy eating style option.

What is a Mediterranean eating pattern?

Before we take a deeper look into the study, let’s first talk about what this eating style looks like. A Mediterranean eating pattern diet is what it sounds like: It’s a way of eating that mimics the traditional eating style of people who live in Mediterranean countries (think Italy, Greece and Spain).

Mediterranean diets incorporate lots of vegetables, fruits, nuts, olive oil, legumes, and grains, especially whole grains, as well as smaller amounts of lean meat, fish, and low-fat dairy.

What did this study test?

The PREDIMED study (Prevention with the Mediterranean Diet) investigated the effects of following a Mediterranean diet on the risk of cardiovascular disease in a cohort of 7,447 older adults between the ages of 55 and 80. These participants were at high cardiovascular risk before joining the study. All of them had either type 2 diabetes or three of the following: smoking, hypertension, elevated LDL cholesterol levels (the “bad” cholesterol), low HDL cholesterol levels (the “good” cholesterol), overweight or obesity, or a family history of premature coronary heart disease.

The participants were assigned to one of three experimental diets. One group ate a Mediterranean-style diet with the addition of 1L/week of extra virgin olive oil. The second group also ate a Mediterranean-style diet but with the addition of one 30 g serving of mixed nuts (walnuts, hazelnuts, almonds) a day instead. The third group ate a low-fat diet. Participants consumed their assigned diets for almost five years.

To make sure that participants followed the diets, the research team collected blood and urine samples from randomly selected participants to check for certain markers that indicated whether participants were actually consuming olive oil or nuts. Participants also completed annual questionnaires about their eating habits.

What did the study discover?

The results demonstrated that participants consuming the Mediterranean diet supplemented with either olive oil or nuts were 30% less likely to experience heart attack, stroke, or death from cardiovascular causes than the group on a low-fat diet.

How does this study fit with what we already know about the Mediterranean Diet and heart disease?

Other studies about the Mediterranean diet, including a meta-analysis, a type of study that analyzes separate but similar studies in order to determine trends and significant results in the combined studies, report similar results. In addition, the PREDIMED study is actually the largest randomized clinical trial to date to look at the impact of Mediterranean-style diets on health. Compared with some other studies, the PREDIMED study also provides some of the highest quality evidence (i.e. it has a strong study design) so far, too.

How can I follow a Mediterranean diet?

Vegetables, fruits, nuts, whole grains, healthy unsaturated fats, and legumes are key components of healthy eating patterns appropriate for most people. The 2015-2020 Dietary Guidelines for Americans includes an eating pattern modeled on the Mediterranean diet to help you get started. If you’re at risk for developing cardiovascular disease or looking for ways to adopt a more healthy dietary pattern, following a Mediterranean diet more closely may be a smart choice.

This blog post was written by Julie Hess, PhD the 2017 Sylvia Rowe Fellow.