Mediterranean diet - so good for the heart?

tags: #metanalyses #primary_prevention #secondary_prevention #Lifestyle #prevention #cardiovascular_disease #angina #IHD #healthy_aging #Mediterranean_diet

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The Mediterranean diet is in evidence. Often their health benefits are publicized in the media and the internet. However is it as good for the heart as propagated? Read the following text and learn more!

Randomized clinical trials versus observational studies

Wherever possible and available, the best medical evidence to prove whether or not a treatment works comes from randomized controlled trials. If this is not the case, observational studies may be used to raise hypotheses of association (they do not prove cause and effect). The best scientific evidence for any medical treatment comes from the compilation of several good quality randomized controlled trials. In the case of the Mediterranean diet, there are several randomized clinical studies published on the subject. So it makes little sense to use observational studies to try to answer whether or not the Mediterranean diet helps protect us against heart disease.

What does the compilation of randomized clinical trials on the Mediterranean diet tell us?

UK researchers published an analysis compiling 37 randomized clinical studies on the subject (several compilation studies are called systematic review/meta-analysis) from Cochrane. Most studies (22 studies) designed for people who had no heart disease at the start of the study (we call them primary prevention studies). The other studies evaluated people with heart disease (we call secondary prevention studies).

These studies (meta-analysis) are extensive - for example, the article in question has 154 pages, divided into four sections of analyzes comprising 54 sub-analyzes of results. That is, it is a Herculean work of reviewing and compiling the data that the authors need to do. We do not claim to exhaust and detail every publication, but to give you an idea, here's a summary of the review sections:

Section 1. Comparison of Mediterranean diet pattern versus no intervention (or intervention considered minimal) - primary prevention context. It had six sub analyzes.

Section one example: total cholesterol, change from baseline (the Mediterranean vs. no intervention).

Section 2. Comparison of Mediterranean Diet Pattern versus Other Dietary Intervention - Primary Prevention Context. It had 14 sub analyzes.

Section 2 example: cardiovascular deaths (the Mediterranean vs. other diets).

Section 3. Comparison of Mediterranean diet pattern versus standard management in the context of secondary prevention. It had nine sub analyzes.

Section 3 example: all-cause deaths (the Mediterranean vs. standard management).

Section 4. Comparison of the Mediterranean diet pattern versus another dietary intervention in the context of secondary prevention. It had 25 sub analyzes.

Section 4 example: all-cause deaths (the Mediterranean vs. other diets).

Main results

The main results can divide into two parts. Part 1 includes sections one and section two. Both deal with primary prevention (people who had no disease upon entering the study). Part 2 (sections 3 and 4) focus on secondary prevention studies (people with the illness on entering the study) - eg., study analyzing individuals after heart infarction);

The main outcome of primary prevention studies

Mediterranean diet + extra virgin olive oil supplementation or 3 nuts vs. low-fat diet reduced in favor of the Mediterranean diet in absolute terms one stroke per 100 people treated (strokes decreased from 24/1000 to 14/1000) with median follow-up time of 4.8 years. Quality of scientific evidence: moderate.

The principal outcome of secondary prevention studies

Mediterranean diet + canola margarine supplementation vs. usual care showed a reduction in cardiovascular deaths. These findings are of poor scientific quality, according to the researchers, which increases the uncertainty of the usefulness of this information for cardiac patients in clinical practice.

The authors conclude that there are uncertainties (doubts) about the real benefit of the Mediterranean diet for both primary and secondary prevention. At best, the Mediterranean-style benefits are modest in primary prevention (see results above for primary stroke prevention).

From this extensive research, we can make some comments:

• The real benefit of such a popular Mediterranean diet is small or very small compared to what published in the media (primary prevention);
• The advantage of secondary prevention is even more uncertain;
• In terms of safety, the good news is that studies have found no evidence that the Mediterranean diet causes harm to people (doesn't hurt);
• This “exaggeration” in our perception of the Mediterranean diet based on the analysis of observational studies (much more susceptible to false-positive findings).

I particularly like this tasty food style very much, and nothing changes for me in that regard. I just become more aware that in terms of disease prevention, I can't wait long!

Reference:

Rees K, Takeda A, Martin N, Ellis L, Wijesekara D, Vepa A, et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. The Cochrane database of systematic reviews. 2019;3: Cd009825.

link to the original scientific article: click here