Finding yourself confused by the seemingly endless promotion of weight-loss strategies and diet plans? In this series, we take a look at some popular diets—and review the research behind them.
What Is It?
Chances are you have heard of the Mediterranean diet. If you have a chronic condition like heart disease or high blood pressure, your doctor may even have prescribed it to you. It is often promoted to decrease the risk of heart disease, depression, and dementia.
The traditional diets of countries bordering the Mediterranean Sea differ slightly so there are different versions of the Mediterranean diet. However, in 1993 the Harvard School of Public Health, Oldways Preservation and Exchange Trust, and the European Office of the World Health Organization introduced the Mediterranean Diet Pyramid as a guide to help familiarize people with the most common foods of the region. More of an eating pattern than a strictly regimented diet plan, the pyramid emphasized certain foods based on the dietary traditions of Crete, Greece, and southern Italy during the mid-20th century. At that time, these countries displayed low rates of chronic disease and higher than average adult life expectancy despite having limited access to healthcare. It was believed that the diet—mainly fruits and vegetables, beans, nuts, whole grains, ﬁsh, olive oil, small amounts of dairy, and red wine—contributed to their health benefits. The pyramid also highlighted daily exercise and the beneficial social aspects of eating meals together.
How It Works
The Mediterranean diet is a primarily plant-based eating plan that includes daily intake of whole grains, olive oil, fruits, vegetables, beans and other legumes, nuts, herbs, and spices. Other foods like animal proteins are eaten in smaller quantities, with the preferred animal protein being fish and seafood. Although the pyramid shape suggests the proportion of foods to eat (e.g., eat more fruits and vegetables and less dairy foods), it does not specify portion sizes or specific amounts. It is up to the individual to decide exactly how much food to eat at each meal, as this will vary by physical activity and body size. There are additional points that make this eating plan unique:
- An emphasis on healthy fats. Olive oil is recommended as the primary added fat, replacing other oils and fats (butter, margarine). Other foods naturally containing healthful fats are highlighted, such as avocados, nuts, and oily fish like salmon and sardines; among these, walnuts and fish are high in omega-3 fatty acids.
- Choosing fish as the preferred animal protein at least twice weekly and other animal proteins of poultry, eggs, and dairy (cheese or yogurt) in smaller portions either daily or a few times a week. Red meat is limited to a few times per month.
- Choosing water as the main daily beverage, but allowing a moderate intake of wine with meals, about one to two glasses a day for men and one glass a day for women.
- Stressing daily physical activity through enjoyable activities.
The Research So Far
Research has consistently shown that the Mediterranean diet is effective in reducing the risk of cardiovascular diseases and overall mortality. A study of nearly 26,000 women found that those who followed this type of diet had 25% less risk of developing cardiovascular disease over the course of 12 years. The study examined a range of underlying mechanisms that might account for this reduction, and found that changes in inflammation, blood sugar, and body mass index were the biggest drivers.
One interesting finding of this eating plan is that it dispels the myth that people with or at risk for heart disease must eat a low fat diet. Although it does matter which types of fats are chosen, the percentage of calories from fat is less of an issue. The PREDIMED study, a primary prevention trial including thousands of people with diabetes or other risk factors for heart disease found that a Mediterranean diet supplemented with extra virgin olive oil or nuts and without any fat and calorie restrictions reduced the rates of death from stroke by roughly 30%. Most dietary fats were healthy fats, such as those from fatty fish, olive oil, and nuts, but total fat intake was generous at 39-42% of total daily calories, much higher than the 20-35% fat guideline as stated by the Institute of Medicine. Risk of type 2 diabetes was also reduced in the PREDIMED trial.
There has also been increased interest in the diet’s effects on aging and cognitive function. Cell damage through stress and inflammation that can lead to age-related diseases has been linked to a specific part of DNA called telomeres. These structures naturally shorten with age, and their length size can predict life expectancy and the risk of developing age-related diseases. Telomeres with long lengths are considered protective against chronic diseases and earlier death, whereas short lengths increase risk. Antioxidants can help combat cell stress and preserve telomere length, such as by eating foods that contain antioxidants nutrients like fruits, vegetables, nuts, and whole grains. These foods are found in healthy eating patterns like the Mediterranean diet. This was demonstrated in a large cohort of 4676 healthy middle-aged women from the Nurses’ Health Study where participants who more closely followed the Mediterranean diet were found to have longer telomere length.
Another Nurses’ Health Study following 10,670 women ages 57-61 observed the effect of dietary patterns on aging. Healthy aging was defined as living to 70 years or more, and having no chronic diseases (e.g., type 2 diabetes, kidney disease, lung disease, Parkinson’s disease, cancer) or major declines in mental health, cognition, and physical function. The study found that the women who followed a Mediterranean-type eating pattern were 46% more likely to age healthfully. Increased intake of plant foods, whole grains, and fish; moderate alcohol intake; and low intake of red and processed meats were believed to contribute to this finding.
- There is a risk of excess calorie intake because specific amounts of foods and portion sizes are not emphasized, which could lead to weight gain. It might be helpful to use the Mediterranean Diet Pyramid, which provides guidance on specific types of foods to choose, along with a balanced plate guide such as the Harvard Healthy Eating Plate, which gives a better indication of proportions of food to eat per meal. However, it is important to note that—probably in part due to the higher intake of olive oil and less processed foods—the Mediterranean dietary pattern provides satiety and enables long term adherence. In one of the most successful weight loss trials to date, those assigned to the Mediterranean diet maintained weight loss over a period of six years.
- Research supports the health benefits of a Mediterranean-style eating pattern that includes several different foods. It is the combination of these foods that appear protective against disease, as the benefit is not as strong when looking at single foods or nutrients included in the Mediterranean diet. Therefore it is important to not simply add olive oil or nuts to one’s current diet but to adopt the plan in its entirety.
Research supports the use of the Mediterranean diet as a healthy eating pattern for the prevention of cardiovascular diseases, increasing lifespan, and healthy aging. When used in conjunction with caloric restriction, the diet may also support healthy weight loss.