Resumen de La dieta mediterránea y su relación con enfermedades crónicas; obesidad, cáncer gástrico y enfermedades coronarias
The research undertaken for this thesis aimed to investigate further the possible role of the MD on reducing risk of chronic diseases, focusing on three chronic diseases and exploring areas where there were specific gaps in the scientific literature. The relationship between degree of adherence to a MD and risk of GC and CHD were investigated in two prospective studies carried out within the EPIC cohort. In order to estimate degree of adherence to a MD the rMED score was constructed, which captures the key elements of a MD. A systematic review of the epidemiological evidence on the MD and overweight and obesity was also undertaken. The results of this research are compatible with the hypotheses that higher adherence to a MD is associated with a lower risk of incident GC and incident CHD, and may play a role in preventing overweight and obesity. The research findings support and expand on the current knowledge on the beneficial effects of the MD on CHD and cancer, showing that high compared with low adherence to an rMED was related to a reduction the incidence of CHD by 40% and of GC by 33%.
GC was also analysed according to anatomical location and histological types, because they may be aetiologically heterogeneous. Despite the fact that previous studies in EPIC found that the relationship between certain dietary factors and GC varied by sub-site and sub-type there was no evidence of heterogeneity in our study. However, it is difficult to draw any firm conclusions from these results, as there could be true differences that were undetectable due to relatively imprecise estimate for the subgroups of GC.
As would be expected, the association between the MD and GC and CHD was similar for men and women (there was no evidence of interaction by sex). In both studies, there was evidence of a significant trend in the relationship between the disease and exposure; the risk of GC and CHD progressively decreased as the rMED score increased from low to high. The presence of a dose-response gradient is one of the criteria for assessing the strength of evidence of a relationship and can further support the observed relationship, even though cohort studies alone are unable to deduce causality.
In terms of the relationship between the MD and overweight and obesity, the systematic review revealed that the epidemiological evidence is still limited, as only 23 studies have explored this relationship. The majority of the studies were dietary intervention trials, followed by cross-sectional studies and very few cohort studies. Two-thirds (13) of the studies provided evidence that adhering to a MD was associated with less overweight and obesity or promoted more weight loss (when focusing on the 18 studies where weight was one of the main outcomes). Despite the lack of consistency, the evidence points towards a possible role of the MD in preventing overweight and obesity and the extent of the protective effect of the MD was reasonably strong in some cohort and intervention studies. The systematic review underscored the need for further research to substantiate these findings.
The results of the thesis support the evidence that the MD is associated with reduced risk of several important chronic diseases (GC, CHD and perhaps overweight and obesity), which is of public health relevance for primary prevention of these diseases. Nutritional policies and public health interventions should consider the extent of the benefits gained from following a MD pattern, given the tendency of societies to shift toward a more westernised and globalised dietary pattern and the increasing global burden of these chronic diseases.
