What about the Mediterranean diet? Isn’t that a healthy way of eating?

Extract from the book Eating Plant-Based, Scientific Answers to Your Nutrition Questions (updated version Jan 2023) By Dr Shireen Kassam and Dr Zahra Kassam

Yes, this is correct. The Mediterranean diet is a healthy diet pattern, which is why for 6 years in a row it has been voted the ‘best diet overall’ by a panel of experts for the US World and News Report on best diets (2023). There are a few things to consider before concluding whether the Mediterranean diet is better than a 100% plant-based diet. The Mediterranean diet is not just a single diet because the region is large with a variety of traditional diets. 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 may be even grilling fish on an open barbecue. In fact, Sardinia in Italy and Ikaria in Greece are both Blue Zones, regions of the world where people live the longest and healthiest lives and have the greatest chance of living to 100 years old. But what is it about the Mediterranean diet that makes it so healthy? Well it turns about that researchers have asked just this question (1). What they found when analysing the dietary data from more than 20,000 men and women from Greece was that the components of the diet that are associated with the health benefits are the vegetables, legumes, nuts, fruits and unsaturated fatty acids (from plant sources). The foods that did not appear to impact health outcomes in the Mediterranean diet are dairy, fish, and meat. 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.

The PREDIMED study is always cited as the one that proves how good the Mediterranean diet is for cardiovascular health (2). This study randomised 7447 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 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. The main difference in outcome was in a combined reduction in the chance of suffering a heart attack or stroke or dying from CVD. 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. However, there was NO reduction in the risk of death. In contrast, when the PREDIMED study was analysed using the plant-based diet index there was a significant reduction in the risk of all cause and cardiovascular mortality in those consuming a diet with a high plant-based diet score suggesting once again that the whole plant foods in the Mediterranean diet are those conferring the benefit (3). 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’.

There are very few direct, head-to-head comparisons of the Mediterranean diet versus a 100% plant-based diet. There has been one of a Mediterranean diet versus a vegetarian diet (4,5). The CARDIVEG study randomly assigned 118 overweight participants with high blood lipids or glucose, but who were not on any medication, to either one of the two diet patterns. 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, with no significant differences between them. However, 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. In another very small study comparing the vegan diet to the Mediterranean diet for cardiovascular health in 24 young, healthy volunteers, the Mediterranean diet led to improvements in microvascular function and the vegan diet led to a greater reduction in total cholesterol and weight loss (6). 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, the long anticipated results of a head-to-head comparison of the Mediterranean diet and a low-fat WFPB diet were published (7). A low-fat WFPB diet is a healthy version of a vegan diet, which in clinical studies has been shown to have excellent effects on health outcomes. Prior research has shown that a low-fat WFPB diet (meaning avoidance of added processed oils) has the ability to halt the progression of atherosclerosis and in some cases even shown regression of atherosclerotic plaques (8–10).

So, what did this new research show? The study randomised 62 overweight adults to either a Mediterranean or low-fat 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 well-known PREDIMED study, described above, 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.

What were the results? 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.

All in all, the healthy vegan diet held its own against the Mediterranean diet, and in some areas outperformed. The authors hypothesise that the greater reduction in blood pressure in the Mediterranean diet group may have been due to more consumption of vitamin E in olive oil and its antioxidant function. Dairy and nut consumption, which is included in the Mediterranean diet, may have had a lowering effect on blood pressure. We wonder how the vegan diet would have fared with a daily tablespoon of flaxseed or portion of nuts added (see Chapter 9). Nonetheless, these results go some way to explaining why the Ornish low-fat WFPB diet that has been voted the top heart healthy diet for 10 years in a row by the US World and News Report.

Researchers have tried to improve upon the traditional Mediterranean diet by adding more plant foods, less meat, green tea, walnuts and Mankai (duckweed, discussed in Chapter 10), the so-called ‘Green Mediterranean diet’. No surprise, studies show that this ‘greener’ version outperforms the standard version (11,12).

Our conclusions are that the Mediterranean diet is beneficial because of the emphasis on whole plant foods. The other components such as fish, poultry, alcohol and dairy for example act to make this diet more acceptable within our cultural and societal norms but are not essential components of the diet for health. It is certainly very much better than the typical Western-style diet pattern.

References

1. Trichopoulou A, Bamia C, Trichopoulos D. Anatomy of health effects of Mediterranean diet: Greek EPIC prospective cohort study. BMJ. 2009;
2. Estruch R, Ros E, Salas-Salvadó J, Covas M-I, Corella D, Arós F, et al. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. N Engl J Med. 2018;
3. Martínez-González MA, Sánchez-Tainta A, Corella D, Salas-Salvadó J, Ros E, Arós F, et al. A provegetarian food pattern and reduction in total mortality in the Prevención con Dieta Mediterránea (PREDIMED) study. In: American Journal of Clinical Nutrition. 2014.
4. Pagliai G, Dinu M, Mangino A, Cesari F, Giusti B, Gori AM, et al. Comparison between Mediterranean and Vegetarian diets for cardiovascular prevention: The cardiveg study. Nutr Metab Cardiovasc Dis. 2017;
5. Sofi F, Dinu M, Pagliai G, Cesari F, Gori AM, Sereni A, et al. Low-calorie vegetarian versus mediterranean diets for reducing body weight and improving cardiovascular risk profile. Circulation. 2018;
6. Rogerson D, Maçãs D, Milner M, Liu Y, Klonizakis M. Contrasting effects of short-term mediterranean and vegan diets on microvascular function and cholesterol in younger adults: A comparative pilot study. Nutrients. 2018;
7. Barnard ND, Alwarith J, Rembert E, Brandon L, Nguyen M, Goergen A, et al. A Mediterranean Diet and Low-Fat Vegan Diet to Improve Body Weight and Cardiometabolic Risk Factors: A Randomized, Cross-over Trial. J Am Coll Nutr. 2021;
8. Ornish D, Brown SE, Billings JH, Scherwitz LW, Armstrong WT, Ports TA, et al. Can lifestyle changes reverse coronary heart disease?. The Lifestyle Heart Trial. Lancet. 1990;
9. Esselstyn CB, Gendy G, Doyle J, Golubic M, Roizen MF. A way to reverse CAD? J Fam Pract. 2014;
10. Gupta SK, Sawhney RC, Rai L, Chavan VD, Dani S, Arora RC. Regression of Coronary Atherosclerosis through Healthy Lifestyle in Coronary Artery Disease Patients — Mount Abu Open Heart Trial. Indian Heart J. 2011;63:461–9.
11. Tsaban G, Yaskolka Meir A, Rinott E, Zelicha H, Kaplan A, Shalev A, et al. The effect of green Mediterranean diet on cardiometabolic risk; A randomised controlled trial. Heart. 2020;
12. Yaskolka Meir A, Rinott E, Tsaban G, Zelicha H, Kaplan A, Rosen P, et al. Effect of green-Mediterranean diet on intrahepatic fat: the DIRECT PLUS randomised controlled trial. Gut. 2021;