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When we look for high–quality scientific research, we want to see a large sample size, and we also want to see that the study was conducted over a long period of time. In addition, we hope that the scientists were able to control as many variables as possible, considering that they are dealing with people, who are most definitely not all the same and clearly uncontrollable on many occasions. (As a teacher, I know this.) Fortunately, the PREDIMED trial meets many of these criteria fairly well.
PREDIMED stands for “Prevencion con Dieta Mediterranea,” which is Spanish for “I am not sure exactly because I don’t speak Spanish, but I know they were studying the effects of a Mediterranean diet on various health outcomes.” This study, which began in 2003 and lasted until 2010, investigated the relationship between a Mediterranean diet and various health outcomes. Fortunately for me, their results have all been published in English.
Before we get into specifics, let’s define what we mean by a “Mediterranean diet.” This type of eating pattern is generally high in fruits and vegetables, and also includes plenty of legumes (beans), fish, whole grains, nuts and seeds, and olive oil. You’ll find a more moderate intake of dairy products and wine, with a lower overall consumption of certain foods, including red and processed meats and foods with a high sugar content.
To design and oversee this large-scale research study, scientists in Spain collaborated with others from around the world, including researchers from Columbia University, Harvard University, and Loma Linda University. They enrolled 7,447 participants between the ages of 55-80, all of whom were judged to be at “high risk” of cardiovascular disease (CVD) at the beginning of the study. This means that all of the participants in the study had three or more risk factors for CVD, including Type 2 diabetes, high blood pressure, smoking, poor cholesterol profiles, obesity, and/or a family history of CVD.
Participants were divided into three groups:
These three groups were then followed for about 5 years to assess the effect of these dietary patterns on their overall health, and specifically their cardiovascular outcomes. None of the participants were asked to limit calorie intake or increase exercise.
If you want to watch a short video (about 15 minutes) as an introduction to their study methods, here is a link to one:
The video is called “Presentation of the Final Results [PREDIMED]”, and it explains how the participants were selected and placed into groups so that each group was as similar as possible to the other groups.
Of course, as I mentioned before in a previous chapter, one limitation to this type of research is that it can be difficult to ascertain whether participants in a study followed the prescribed dietary recommendations, so it’s important to know that the researchers conducted interviews frequently with the participants to see if they were following the guidelines outlined in the plans. To measure adherence, participants met with dieticians who determined if they were, indeed, eating according to recommendations. A questionnaire was used to rate participants’ levels of compliance. It is possible that participants weren’t honest with the researchers about what they were eating? Sure.
At the conclusion of the study in 2013, initial results were published, in a paper called Primary Prevention of Cardiovascular Disease with a Mediterranean Diet, which is available at this link:
http://www.unav.edu/departamento/preventiva/files/file/predimed/NEJM_PREDIMED_printed.pdf
At that link, you can find more details about how the study was conducted. Remember: it’s always best to look at something for yourself in order to draw conclusions about results, rather than just take my word for it.
The most exciting information in this paper is found in the discussion section. According to the authors, they found that the two Mediterranean diet groups had a 30% risk-reduction for cardiovascular events during the study, when compared to the control diet group. The two Mediterranean diet groups also had a lowered risk of stroke. Remember that the participants were selected because they were at a high risk for cardiovascular disease: they all had 3 or more risk factors, and they were all between the ages of 55-80. To substantially lower the risk for cardiovascular events within this population is impressive, since they were all considered to be high-risk at the beginning of the study. These results were all due to dietary interventions alone, and not based on medications.
To learn more about the PREDIMED trial specifically, all of their published research is available to you at their website:
http://www.predimed.es/publications.html
Through this link, you have access to paper after paper showing the amazing benefits attributed to the Mediterranean diet. I encourage you to dig into these studies to see what you can learn.
The PREDIMED study is not the only one to investigate the benefits of a Mediterranean diet. In fact, scientists have been investigating the effectiveness of a Mediterranean diet for years. While PREDIMED is the most ambitious study undertaken thus far, other studies also support this particular dietary pattern. Some of the key research from these studies has been summarized in a paper called Protective Effects of the Mediterranean Diet on Type 2 Diabetes and Metabolic Syndrome, which is available here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4807638/
This paper does an excellent job discussing many of the various studies and what was found. I highly encourage you to read it.
In one meta-analysis of studies related to the Mediterranean diet, researchers found 20 studies with dietary interventions that lasted for more than 6 months. Overall, they found that the Mediterranean dietary pattern showed greater improvement in both glycemic control and insulin sensitivity when compared to other diets. Based on what we know about insulin and weight management, we understand that insulin sensitivity is associated with better health outcomes long-term.
Besides clinical trials, some of the Mediterranean diet studies were epidemiologic in nature, meaning that the study attempted to link specific health results to certain factors within the participants’ lifestyles. While these types of studies do have some limitations, and may not give us as much information as well done clinical trials, common results were discovered among these studies:
One specific study is interesting because it takes us back to the Blue Zone located in Loma Linda, California. Results of a study (using the Adventists that we learned about earlier) were reported in a paper called Intake of Mediterranean Foods Associated with Positive Affect and Low Negative Affect, which can be found here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790574/pdf/nihms512849.pdf
By now, it shouldn’t surprise you that results of this study indicated that the more fresh vegetables, fruits, olive oil, nuts, and legumes participants ate, the better their overall health outcomes.
So, you might ask: do we have sufficient evidence to point toward a Mediterranean dietary pattern as superior to other eating styles? A group of experts from France, Germany, Italy, Portugal, Spain, and Switzerland would say that the answer to that question is yes.
Recently, this team of experts (including cardiologists, endocrinologists, and internists) got together and examined all of the evidence related to dietary recommendations and health outcomes. Their 2017 report is called Is There a Role for Lifestyle Changes in Cardiovascular Prevention? What, When, and How? The full report in pdf format can be found here:
http://www.sciencedirect.com/science/article/pii/S156756881730020X
Their overall dietary recommendations can be seen throughout the paper. Based upon the most recent scientific understandings, this group of physicians felt strongly that the best dietary pattern includes plenty of fruits and vegetables, seeds, nuts, fish, whole grains, and olive oil. As you know, this is typical of what is found in a Mediterranean diet. Rather than think of specific foods found only in the Mediterranean region, however, the physicians felt that anyone could adapt these recommendations to include foods that are available to us locally that meet these criteria. That is: eat plenty of whatever fruits, vegetables, seeds, nuts, fish, and whole grains are available to you.
These experts also agreed that there is no evidence to support a low-fat diet, though they did recommend getting most of the fat in our diets from plant sources such as olive oil. (In a later chapter about genetic differences, we will see that some people need to worry more about saturated fat than others, based on individual differences.)
To read what some other experts have to say about the Mediterranean dietary pattern, including their recommendations of what to eat and how it has been shown to affect various health outcomes, you can read Definitions and Potential Health Benefits of the Mediterranean Diet: Views from Experts Around the World:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4222885/pdf/12916_2014_Article_994.pdf
In this paper, 8 different experts share their thoughts. In addition, there is an image called the Mediterranean Diet Pyramid (Figure 5) that includes specific dietary guidelines for what a Mediterranean dietary pattern generally looks like.
While we know that there are limitations to be found with all scientific studies, the accumulation of evidence is pretty compelling. If you have been paying attention (and the teacher in me hopes that you have), you may have noticed that the types of foods associated with a healthy Mediterranean diet are similar to the foods eaten in the Blue Zones. These foods are also the ones that seem to feed our gut microbiomes the best.
Now, let’s put all of this information together and see what foods we can confidently add to our diets so we can Feast Without Fear!