Adherence to Mediterranean diet and health status: meta-analysis
BMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a1344 (Published 11 September 2008) Cite this as: BMJ 2008;337:a1344
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We certainly would agree that further meta-analyses could be
strengthened by considering the Moslem community as a group with specific
dietary habits, and where neither pork nor alcohol forms part of what is
normally consumed in Northern Mediterranean regions, although such
communities co-exist here.
Perhaps Sofi et al. could provide more data as to ethnic differences. We
made a pilot study (ms. in preparation) regarding the dietary habits in
two immigrants communities: one was Moroccan and shows a shift in food
intake patterns.
Competing interests:
None declared.
Competing interests: No competing interests
I would be interested to know how many per cent of these people were
moslem . They dont eat pork .They are mostly poor, they dont drink
Competing interests:
None declared
Competing interests: No competing interests
The Mediterranean diet is not only a single entity, as the authors
assumed. As a health source, in several studies, it has been related to
NCD (Non Communicable Disease) prevention. Its´ generalisation as a food
pattern allows study inclusion in a broad sense without specific
differences from each country, eg Greece (1), in this meta-analysis.
However, to contemplate the Mediterranean diet without specific fish and
shellfish intake evaluation, increases sample heterogeneity and shifts the
diet model to diets within health promotion strategies and general
recommendations. This could give pattern differing from that of a specific
Mediterranean pyramid (2), beyond its´ consumption in these countries,
which consequently affect exclusion criteria. Olive oil use as an integral
part of the Mediterranean diet has been studied longer (3), focussing on
its´ contribution first as MUFAs, along with alpha-linolenic acid. Eating
fish in Mediterranean countries is a generalised practice which
contributed to the omega-3 intake eicosapentanoic acid and docosahexanoic
acid, and therefore modifies the omega-6/omega-3 ratio, parameter which
reflects a health quality diet (4). The change of this parameter is
related to NCD. The main factor responsible for mortality by NCD,
particularly cardiovascular diseases or cancer, was associated with fish
consumption in making the low incidence of mortality in Japan rather than
in the Mediterranean countries and last of all the Americans (5,6).
References
1 - Simopoulos A What is so special about the diet of Greece? The
scientific evidence. World Rev Nutr Diet 2005;95:80-92.
2 - Willett WC, Sacks F, Trichopoulou A, Drescher G, ferro-Luzzi A,
Helsing E, Trichopoulos D. Mediterranean diet pyramid: a cultural model
for healthy eating. Am J Clin Nutr.1995 Jun;61 (6 Suppl):14025-14065.
3 - Perez-Jimenez F, Alvarez de Cienfuegos G, Badimon L, Barja G,
Battino M, Blanco A, Bonanome A, Colomer R, Corella-Piquer D, Covas I,
Chamorro-Quiros J, Escrich E, Gaforio JJ, Garcia Luna PP, Hidalgo L,
Kafatos A, Kris-Etherton PM, Lairon D, Lamuela-Raventos R, Lopez-Miranda
J, Lopez-Segura F, Martinez-Gonzalez MA, Mata P, Mataix J, Ordovas J,
Osada J, Pacheco-Reyes R, Perucho M, Pineda-Priego M, Quiles JL, Ramirez-
Tortosa MC, Ruiz-Gutierrez V, Sanchez-Rovira P, Solfrizzi V, Soriguer-
Escofet F, de la Torre-Fornell R, Trichopoulos A, Villalba-Montoro JM,
Villar-Ortiz JR, Visioli F. International conference on the healthy effect
of virgin olive oil.
Eur J Clin Invest. 2005 Jul;35(7):421-4. Review.
4 - Simopoulos AP The importance of the omega-6/omega-3 fatty acid
ratio in cardiovascular disease and other chronic diseases. Exp Biol Med
(Maywood). 2008 Jun;233(6):674-88. Epub 2008 Apr 11.
5 -Tokudome S, Nagaya T, Okuyama H, Tokudome Y, Imaeda N, Kitagawa I,
Fujiwara N, Ikeda M, Chiho G, Ichikawa H, Kuriki K, Takekuma K, Asuka S,
Hirose k, Usui T. Japanese versus Mediterranean Diets and Cancer. Asian
Pacific J of Cancer Prevention, 2000 Vol 1:61-6.
6 -Tokudome S, Ichikawa Y, Okuyama H, Tokudome Y, Goto C, Imaeda N,
Kuriki K, Suzuki S, Shibata K, Jiang J, Wang J, Takeda E. The
Mediterranean vs the Japanese diet. Eur J Clin Nutr. 2004 Sep;58(9):1323;
author reply 1324
Competing interests:
None declared
Competing interests: No competing interests
I was most interested in your article. As a non statistician I am
particularily interested in the benefit to the man or woman in front of
me.
For instance my understanding of dropping an average blood pressure
from 160/90 to 140/ 80 is that the NNT are about 125 for 5 years to
prevent a Cardiac or Stroke Event.
What is the NNT and Absolute risk reduction to be afforded by this diet??
It looks most encouraging.
Competing interests:
None declared
Competing interests: No competing interests
I am not satisfied that the studies reviewed are sufficiently wide
ranging to draw meaningful conclusions. In addition, the reviewed studies
are far too parochial.
For example:
1 Have causes of death for the indigenous people in each of the
countries surrounding the Mediterranean been evaluated to determine ( as a
percentage of the population ) how they materially differ, if at all, from
other European countries ?
2 Is their any significant difference between causes of mortality in
Mediterranean countries than those in Scandinavia ?
3 With regard to both of the above what differnces are there of
significance, if any, in longevity of live in the respective countries ?
Similarly, is there any material difference in the repective country's
morbidity ?
4 None of the studies appear to compare the Mediterranean countries
with other "mature" economies around the globe. Why, for example, does
Japan ( the second largest economy in the world ) have longevity of life
far greater than in the Mediterranean countries? In addition, analysis of
the reason for longevity of life being far greater for residents of the
southern Japanese island of Okinawa being greater than for the rest of
Japan would be a useful piece of research.
In summary, the studies evaluated are not in any way sufficiently
widespread as to draw valid and meaningful conclusions.
Best wishes.
Colin Williams
Competing interests:
None declared
Competing interests: No competing interests
Are the olives just as green on the other side of the Mediterranean? Meta-analysis of a concept rather than an intervention.
Considering the empirical and public health attention to the
Mediterranean diet, a meta-analysis of studies examining the association
between adherence to this diet and associated mortality and morbidity
outcomes might further our understanding of how nutritional patterns in
accordance with this diet may be of both individual and public health
importance. Sofi et al. [1] reported some potentially important meta-
analytic findings. However, unclarity as to what is understood by the
Mediterranean diet makes these findings suggestive at best. This is
compounded by additional methodological concerns.
Foremost, Sofi et al. do not specify what constitutes the
Mediterranean diet – as if they assume that it is generally known or that
it is a narrowly defined and operationalized diet. Instead, they provide
a definition of the overall composition (7-9 elements), rather flatly so;
without prioritization and proportioning as provided, for instance, in the
Mediterranean diet pyramid [2]; ignoring it is based on dietary habits
from the 1960s; and skirting the call for redefinition [3]. Instead, the
authors focus on adherence to various elements of not much more than a
concept (the Mediterranean diet), operationalizing this adherence (and not
the concept) as the summed extent to which people consume above-median
amounts of each element – a statistical boundary without much empirical
substantiation and devoid of statistical context.
The lack of clarity is compounded by the omission of nutrition-
impacting variation within the Mediterranean region - in terms of topo-
and hydrography, agri- and pesciculture, cultures and religions, and
economic variations. Should one assume that the nutritional pattern
referred to as the Mediterranean diet show a certain uniformity across
this large an area? And how far should one leave the 46000km of shoreline
before dietary patterns begin to diverge significantly? Furthermore, how
does the (ill-defined) Mediterranean diet differentiate itself from other
regional diets that are comparable in part or in all nutritional
components - e.g., diets along the Atlantic coast of Morocco, Portugal,
Spain and France? In the end, what is the Mediterranean diet, where is it
found, how is it operationalized, and how much does it vary across
geography and populations? In the absence of answers to these questions,
the Mediterranean diet is at best a concept, certainly not a definable
intervention.
Other concerns compound this primary problem of not meta-analyzing an
intervention but rather a concept. Might there be a study cohort effect,
as the Sofi et al. meta-analysis is limited to studies in which adherence
to the diet, not the diet itself, could be quantified? Granted, and using
randomized clinical trial terminology, by studying adherence to the
Mediterranean diet one asserts a degree of “adherence to the protocol”.
Yet this occurs at the risk of a collusion between adherence to a concept
and adherence to a replicable (or at least imitable) intervention
protocol. Might there be a “lead author” effect as five of the nine
studies included in Figure 2 are by two lead authors, including one
covering one-third of the studies? As Sofi et al. argue correctly,
interactions between the components of a dietary pattern must be
considered. However, what this interaction is and how it is influenced by
nonnutritional factors is not addressed: one does not eat in isolation and
instead one is thought familially and socially certain nutritional
patterns – based on (seasonal) availability. Thus, Sofi et al.’s decision
to combine studies with subjects indigenous to the Mediterranean region
and studies involving subjects from, for instance, the US merits a
convincing argument.
Notwithstanding the high position of meta-analysis in the hierarchy
of evidence, sometimes individual and public health might be served better
by an integrative review of a large corpus of studies that addresses the
full range of scientific issues from conceptualization,
operationalization, study design, statistical analysis, to interpretation.
The Sofi et al. findings may provide some direction, however the
destination remains elusive.
References
[1] Sofi F, Cesari F, Abbate R, Gensini GF, Casini A. Adherence to
Mediterranean diet and health status: a meta-analysis. BMJ 2008;337:1344.
doi:10.1136/bmj.a1344.
[2] Willett WS, Sacks F, Trichopoulou A, Drescher G, Ferro-Luzzi A,
Helsing E, et al. Mediterranean diet pyramid: a cultural model for
healthy eating. Am J Clin Nutr 1995;61:1402-6.
[3]Serra-Majem L, Trichopoulou A, de la Cruz JN, Cervera P, Alvarez
AG, La Vecchia A, et al. Does the definition of Mediterranean diet need
to be updated ? Publ Health Nutr 2004;7:927-9.
Competing interests:
None declared
Competing interests: No competing interests