The Mediterranean diet: how does it compare to a plant-based diet?

By Dr Shireen Kassam, Director of Plant-Based Health Professionals UK

The Mediterranean diet is one of the most well-researched dietary patterns in the medical literature and is universally considered to be one of the healthiest ways to eat.  The diet is best known for its positive impact on cardiovascular health.

The Mediterranean diet is not just a single diet because the region itself is large with a variety of traditional ways of eating. The usual image that comes to mind when thinking about the Mediterranean diet is sitting on a white, sandy beach on a warm summer’s day sipping red wine and eating olives and maybe even grilling fish on an open barbecue. In fact, Sardinia in Italy and Ikaria in Greece are both Blue Zones, diverse regions of the world where people live the longest and healthiest lives and have the greatest chance of living to 100 years old.

What is important to understand is that the Mediterranean diet is beneficial because of the emphasis on whole plant foods.

Evidence supporting the Mediterranean diet

Primary prevention

The PREDIMED study is usually cited as the landmark study that demonstrated that the Mediterranean diet is good for cardiovascular health. This study randomised 7,447 participants who were at high risk of developing cardiovascular disease (CVD) into three groups; two intervention groups and a control group. The intervention groups were randomised to a Mediterranean diet with added extra-virgin olive oil (50 grams/4 tablespoons) or a daily portion of nuts (30 grams).

After following the participants for 4.8 years, the results showed only minimal weight loss in each group, with no difference between the intervention and control groups. However, both intervention groups had a lower combined risk of experiencing a heart attack, stroke, or dying from CVD compared to control. The main contributor to this significant finding was a 40% reduction in the risk of stroke in the nut consuming group rather than any reduction in heart attacks or risk of dying from CVD. There was no reduction in the risk of death.

Secondary prevention

The Lyon Diet Heart Study was a randomised secondary prevention trial aimed at testing whether a Mediterranean diet could reduce the risk of recurrent myocardial infarction (heart attack) after a first myocardial infarction.

The intervention arm on the Mediterranean diet included eating alpha-linolenic acid (omega-3 fatty acid) and linoleic-acid (omega-6 fatty acid) supplemented margarine in place of butter and cream. The study was stopped early due to the benefits in the Mediterranean diet group, which showed a significant reduction in recurrent cardiac events and death.

The CORDIOPREV study (Coronary Diet Intervention With Olive Oil and Cardiovascular Prevention) is the latest randomised study of a Mediterranean diet. 1002 participants with heart disease were either assigned to a Mediterranean diet or a low-fat diet and followed for 7 years. The goal in the Mediterranean diet group was to consume >35% of calories from fat mainly from olive oil. In the low-fat group the aim was to lower fat consumption to <30% of calories. Protein consumption was intended to remain constant and hence fat was replaced by carbohydrates. In the Mediterranean diet group, fat was increased by consuming more olive oil, nuts and fatty fish. In the low-fat group these foods were reduced and replaced by more whole grains, legumes and low-fat dairy. Of note, the low-fat group did not achieve the macronutrient goals, so this cannot truly be deemed a low-fat intervention.

Nonetheless, the results showed a significant benefit for the Mediterranean diet with participants having a 26% lower overall rate of cardiovascular events and mortality. Those with the greatest adherence to the Mediterranean diet had a 40% reduction in cardiovascular events.

What makes the Mediterranean diet healthy?

When researchers analysed the dietary data of more than 20,000 men and women in Greece, they found that vegetables, legumes, nuts, fruits and unsaturated fatty acids (from plant sources) were the components of the Mediterranean diet associated with health benefits. Dairy, fish, and meat as part of the Mediterranean diet did not appear to confer health benefits. So, the diet is healthy because of the strong emphasis on the plant-based foods and not because of the animal-based foods that are included.

When the PREDIMED study data were analysed using the provegetarian score, there was a significant reduction in the risk of all cause and cardiovascular mortality in participants consuming a diet with higher intakes of plant-based foods. The authors of this analysis concluded ‘we provide evidence to support that the simple advice to increase the consumption of plant-derived foods with compensatory reductions in the consumption of foods from animal sources confers a survival advantage to older subjects at high cardiovascular risk’.

Can the Mediterranean diet be made even healthier?

Researchers have tried to improve upon the traditional Mediterranean diet by adding more plant foods, less meat, green tea, walnuts and Mankai (duckweed), the so-called ‘Green Mediterranean diet’.

In randomised studies, this more plant-based version out-performed the traditional Mediterranean diet for improvements in cardiometabolic risk factors and fatty liver disease. These additional benefits of the Green Mediterranean diet correlate with increased intake of plants and reduced intake of meat and may be due to enhanced effects on the health of the gut microbiome.

Comparing Mediterranean diet to vegetarian and vegan diets

There are now a few, head-to-head comparisons of the Mediterranean diet versus a 100% plant-based diet or vegetarian diet.

The CARDIVEG study randomly assigned 118 overweight participants with high blood lipids or glucose, who were not on any medication, to either a vegetarian or Mediterranean diet. It was a 3-month intervention with both diet groups having the same but reduced calorie intake. After 3 months both groups crossed over to the other diet pattern.

Both diets were equally effective in reducing body weight, body mass index, and fat mass. The vegetarian diet was more effective in reducing total cholesterol, low-density lipoprotein (LDL) cholesterol and insulin levels, whereas the Mediterranean diet led to a greater reduction in triglyceride levels.

The OMNIVEG study compared the Mediterranean diet with a vegan Mediterranean diet in 14 healthy, physically active men. The results showed that the vegan version resulted in greater reduction in total and LDL-cholesterol and blood pressure and without compromising markers of athletic performance.

Another small study compared the vegan diet to a Mediterranean diet in 24 young, healthy volunteers. The Mediterranean diet led to improvements in microvascular function and the vegan diet led to greater reductions in total cholesterol and body weight. It is worth noting that the vegan diet in this study was relatively high in fat with participants consuming 35% of calories from fat.

At the start of 2021, a larger head-to-head comparison of the Mediterranean diet versus a low-fat vegan diet was published. The study randomised 62 overweight adults to either a Mediterranean or vegan diet for 16 weeks. After a 4-week washout period in which participants returned to their baseline diet, they then crossed over to the alternate diet for a further 16 weeks. Both groups could eat as much as they wanted. The Mediterranean diet followed the diet in the PREDIMED study and included 50g of olive oil daily. The vegan diet was intended to contain approximately 75% carbohydrates, 15% protein and 10% fat from whole plant sources, no added oil and a B12 supplement. Body weight, blood pressure, body composition, insulin resistance and glucose tolerance were measured before and after each phase.

The actual fat intake was 43% of calories in the Mediterranean group and 17% in the vegan group. Although participants could eat as much as they wanted, the vegan group consumed around 500 less calories per day and had a higher intake of fibre and lower intakes of saturated fat and cholesterol. The vegan group lost an average of 6kg, but the Mediterranean diet group lost no weight. The vegan group also had significant reductions in body fat and visceral fat and significant improvements in blood total and LDL-cholesterol levels and insulin sensitivity. These parameters did not change in the Mediterranean diet group. Both groups had reductions in blood pressure but there was a greater effect in the Mediterranean diet group.

Planetary health, cost and inclusivity

Where a fully plant-based or vegan diet has a clear advantage is the impact on planetary health and cost. All animal sourced foods have a greater environmental footprint compared to plant-based foods, regardless of farming methods and place of origin. The emphasis on fish and inclusion of other animal-sourced foods in the Mediterranean diet increase both the environmental impact and cost of the diet.

It’s also worth noting that many cultures around the world will not identify with the Mediterranean diet. Their traditional diet patterns may already be healthy due to an emphasis on healthy plant foods. This includes traditional Asian and African diets.

An Indian adaptation of the Mediterranean may even be healthier than the typical version due to the higher intakes of legumes, wider variety of whole grains such as millet, and the abundance of beneficial spices.

Summary

• The Mediterranean diet is beneficial because of the emphasis on whole plant foods.
• Compared to a typical Western-style diet it has significant benefits for health.
• Dietary components such as fish, poultry, alcohol and dairy may make the diet more acceptable within our cultural and societal norms, but are not essential components.
• Increasing the plant-based component of the Mediterranean results in improvement in body weight, LDL-cholesterol and fatty liver with variable results shown for blood pressure and triglyceride levels.
• The macronutrient ratio of the diet matters less than the quality of food being consumed.
• A fully plant-based diet is better for the environment and cheaper than the Mediterranean diet.
• A plant-based diet is more easily adapted to different cultural and traditional diet patterns, as most of the global population will not identify with the Mediterranean diet.