Last updated on September 13th, 2022 at 01:22 pm
Although I think that most diets are bogus and healthy outcomes are not very well supported by scientific research, I have been a proponent of the so-called Mediterranean diet. It seems to have been linked to lower risks of cancer, cardiovascular disease, and some other chronic health conditions.
The claims of researchers who stated that the so-called Mediterranean diet, rich in plants, olive oil, fish, nuts, and other foods, was linked to lower risks of cardiovascular disease. It was a pivotal and robust cohort study, a powerful form of epidemiological study that sits near the top of the hierarchy of medical research, that influenced a lot of recommendations about the proper diet for people. The study was so powerful that I switched to that diet personally.
But lucky for the planet, science is self-correcting, and some aspects of the original study caused concerns, and the Mediterranean diet study was retracted and republished with corrections.
Does this mean that the Mediterranean diet was and is bogus? No, but let’s take a look at the whole story.
The Mediterranean diet
The Mediterranean diet is a diet that is common to the eating habits of people living in areas of the Mediterranean, including Greece, Southern Italy, and Spain. The diet generally includes proportionally high amounts of olive oil, legumes, unrefined grains, fruits, and vegetables. It also includes moderate to high consumption of fish, moderate consumption of dairy products (generally, cheese and yogurt), moderate wine consumption, and low consumption of other types of meat foods.
During the 1940s and 50s, scientists observed that people who consumed these diets seem to be objectively healthier (broadly defined) than other populations that ate other types of diets that included refined grains and non-fish meats.
There is moderate to excellent evidence that the primary health-promoting component of the Mediterranean diet may be olive oil. The oil may be linked to lower all-cause mortality, along with lower risks of cancer, neurodegeneration, and other chronic diseases.
The retracted study examined the benefits of the Mediterranean study with respect to cardiovascular diseases. Although the paper was retracted and republished with significant corrections, we need to remember two points:
- The retraction is just for cardiovascular diseases, the other studies that support the link between the Mediterranean diet and other chronic diseases are, as far as I can tell, still valid and still compelling reasons to continue with the diet.
- The Mediterranean diet is probably still linked to lower risks of cardiovascular disease.
The Mediterranean diet and cardiovascular disease study
The revised and republished study by Ramón Estruch, M.D., Ph.D. et al., published in the New England Journal of Medicine, still shows the importance of the Mediterranean diet, despite the retraction of their first study. The first study was retracted because of a statistical review identified randomization issues in the study. Thus, the revised article comes to similar conclusions as the original one, but the data is a bit less robust.
As with the older study, for the overall study population, the new report cites hazard ratios for a Mediterranean diet supplemented with:
- Nuts (3 servings per week, see note 1), 0.72 (95% CI, 0.54-0.95); or
- Olive oil (4 tablespoons per day), 0.69 (95% CI, 0.53-0.91).
Hazard ratios above 1 mean the diet shows increased risk than a control, whereas a number below 1 means that risks of cardiovascular diseases are lower. So, a Mediterranean diet supplemented with nuts lowers risks by 28%. That diet supplemented with olive oil reduces those risks by 31%. That may not be as robust as the original study, but it appears to be convincing.
The authors then removed the 1588 participants whose randomization was not per-protocol, such as placing couples in the diet arm of the study, and recalculated the hazard ratios::
- Nuts, 0.70 (95% CI, 0.53-0.94); or
- Olive oil, 0.70 (95% CI, 0.53-0.92).
That still looks good to me, although the error is a bit high. Still, the revised study supports the hypothesis that the Mediterranean diet, especially when supplemented with nuts and olive oil, does indeed significantly lower the risk of cardiovascular diseases.
The authors concluded that:
In this study involving persons at high cardiovascular risk, the incidence of major cardiovascular events was lower among those assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts than among those assigned to a reduced-fat diet.
Now, this study focused on those with a pre-existing cardiovascular disease, but I’d have to extend their conclusion that this diet could have a preventative function too. I find this study convincing enough to follow the guidelines, although I’m not a fan of either walnuts or hazelnuts. But I’m sure I could overlook my tastebuds.
Summary
Yes, the authors did mess up the randomization of their study that showed that the Mediterranean diet reduced the risk of cardiovascular events in individuals who had previously diagnosed disease. And, as good scientists do (and bad scientists don’t), they heard criticisms of their analytical techniques, retracted their original paper, revised their analysis removing problematic data, and republished it.
Despite the retraction, the revised study still shows us one thing – the Mediterranean diet, supplemented with olive oil and nuts, may reduce the risk, up to 30%, of cardiovascular events.
Now I wonder if almonds toasted with olive oil makes it even better for my health?
Notes
- The nuts included in this study were almonds, hazelnuts, and walnuts, all provided by Big Nut (giggle). They had no involvement in the study, much like in the pharmaceutical industry, but I’m sure someone will claim that there is some conspiracy.
Citations
- Buckland G, Gonzalez CA. The role of olive oil in disease prevention: a focus on the recent epidemiological evidence from cohort studies and dietary intervention trials. Br J Nutr. 2015 Apr;113 Suppl 2:S94-101. doi: 10.1017/S0007114514003936. Review. PubMed PMID: 26148926.
- Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM, Serra-Majem L, Pintó X, Basora J, Muñoz MA, Sorlí JV, Martínez JA, Fitó M, Gea A, Hernán MA, Martínez-González MA; PREDIMED Study Investigators.. Primary Prevention of Cardiovascular Disease with a Mediterranean Diet Supplemented with Extra-Virgin Olive Oil or Nuts. N Engl J Med. 2018 Jun 21;378(25):e34. doi: 10.1056/NEJMoa1800389. Epub 2018 Jun 13. PubMed PMID: 29897866.
- Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM, Serra-Majem L, Pintó X, Basora J, Muñoz MA, Sorlí JV, Martínez JA, Martínez-González MA. Retraction and Republication: Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. N Engl J Med 2013;368:1279-90. N Engl J Med. 2018 Jun 21;378(25):2441-2442. doi: 10.1056/NEJMc1806491. Epub 2018 Jun 13. Corrected and republished in: N Engl J Med. 2018 Jun 21;378(25):e34. PubMed PMID: 29897867.
- Estruch R, Ros E, Salas-Salvadó J, Covas MI, Corella D, Arós F, Gómez-Gracia E, Ruiz-Gutiérrez V, Fiol M, Lapetra J, Lamuela-Raventos RM, Serra-Majem L, Pintó X, Basora J, Muñoz MA, Sorlí JV, Martínez JA, Martínez-González MA. Retraction and Republication: Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. N Engl J Med 2013;368:1279-90. N Engl J Med. 2018 Jun 21;378(25):2441-2442. doi: 10.1056/NEJMc1806491. Epub 2018 Jun 13. Corrected and republished in: N Engl J Med. 2018 Jun 21;378(25):e34. PubMed PMID: 29897867.
- Piroddi M, Albini A, Fabiani R, Giovannelli L, Luceri C, Natella F, Rosignoli P, Rossi T, Taticchi A, Servili M, Galli F. Nutrigenomics of extra-virgin olive oil: A review. Biofactors. 2017 Jan 2;43(1):17-41. doi: 10.1002/biof.1318. Epub 2016 Sep 1. Review. PubMed PMID: 27580701.
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