Digging into the Mediterranean Diet

In the realm of healthy eating, few diets have garnered as much praise and research-backed support as the Mediterranean diet. Rooted in the traditional dietary patterns of countries like Italy, Spain, and Greece, its origins can be traced back to the mid-20th century. The seminal Seven Countries Study from the 1950s provided evidence that communities in the Mediterranean region had notably reduced rates of cardiovascular disease, which could be attributed to their distinct diet. Rich in fruits, vegetables, legumes, whole grains, nuts, seeds, lean proteins, and healthy fats, this diet stood out as a potential blueprint for healthy living.

In a previous post, I described a remarkable randomized controlled trial (RCT) encompassing approximately 7500 people (aged from 55 to 80) investigating the healthful benefits of the Mediterranean diet. There were two experimental groups (Mediterranean diet with extra virgin olive oil and Mediterranean diet with extra nuts), and one control group which followed a low-fat diet. The study lasted for approximately 5 years, and the measured outcomes were number of heart attacks, stroke and death from cardiovascular disease. Amazingly, the two groups on the Mediterranean diet had a hazard ratio of approximately 0.7 relative to the control group. This meant that the rate of heart attacks and strokes was roughly 30% less in the Mediterranean diet groups compared to the control. 

Unfortunately, a few years later, doubts were raised about the legitimacy of the trial (QH). More specifically, the British epidemiologist John Carlisle ran some statistical tests on the initial trial data which suggested that the two groups had not been properly randomized. His suspicions were borne out when the study authors admitted to mistakes in the randomization: "The authors have now reported that randomization had gone awry for 21% of the participants – 1,588 of the 7,447 people." In other words, roughly 20% of the subjects were not properly randomized. The authors claimed that a re-analysis of the data correcting for the error still showed significant benefits for the Mediterranean diet but the statistical significance was reduced. A more conservative approach would have been just to throw out the 21% that were not properly randomized.

Nevertheless, there have been countless observational studies that have extensively demonstrated the cardiovascular benefits of the Mediterranean diet. Such studies are subject to confounding (e.g. perhaps other lifestyle factors of Mediterranean nations contribute to health) that an RCT is supposed to avoid, but the total sum of supporting evidence is noteworthy. In particular, the diet has been associated with improved Type 2 diabetes, weight management, blood pressure, cholesterol levels and other factors that lead to lower risk of cardiovascular disease. There is even evidence that it reduces the incidence of gallstones (QH), certain types of cancer, and Alzheimer's Disease.

One way of thinking about the Mediterranean diet and its healthful benefits is that it replaces sugar and junk food with healthier substitutes. According to ChatGPT and Bard, the Mediterranean diet is characterized by the following key characteristics:

• High Consumption of Plant-Based Foods: This includes fruits, vegetables, whole grains, nuts, and legumes.
• Olive Oil as the Primary Source of Fat: Olive oil is used instead of butter or other fats. It's high in monounsaturated fatty acids, which are considered healthy fats.
• Moderate Consumption of Fish and Poultry: These are preferred over red meat, which is eaten less frequently.
• Low to Moderate Intake of Dairy Products: This mostly includes cheese and yogurt.
• Limited Red Meat and Processed Foods: These are eaten sparingly.
• Beans, lentils, and other legumes: These foods are a good source of plant-based protein, fiber, and other nutrients.
• Limited amounts of added sugar and refined grains: Sugary drinks, candy, and other processed foods are high in calories and low in nutrients. Fruits and nuts are eaten for dessert.

In sum, plant rather than animal foods, fish and chicken rather than red meat, olive oil instead of saturated fat like animal fat, fruits and nuts rather than added sugars, whole grain versus refined grain, foods like beans, lentils, legumes that contain fiber versus food without fiber, and consuming dairy products for calcium and other nutrients.

One phrase tossed around a lot is that the Mediterranean diet is "more of a lifestyle than a strict plan." Fortunately there are a lot of resources on how to create a plan that fits your lifestyle (e.g. Figure 1). One should be flexible including foods not even from the Mediterranean region. This past week The New York Times ran a series of articles on how to incorporate different aspects of the Mediterranean diet into your meal plans. It is worth a look.

Video 1. The 15 Minute Meal Plan for the Mediterranean Diet