More study types...So do the olives & wine help, or what?

Prospective studies, also known as cohort studies, are longitudinal, follow individuals that have been identified as being “exposed” or not, to something being studied (such as the Mediterranean Diet), and following these two groups to see how many develop the “disease” or condition (in the formerly discussed study, Metabolic Syndrome). One of the big problems with cohort, or prospective, studies is that they can take long periods of time, even decades. Sometimes one can use historical data (such as infant immunization records), and then compare two groups (ones with a specific immunization, or vaccination, and the ones that did not get the vaccine), and then investigate how many in each group had gotten a disease or not (such as measles). This gives an idea of the relationship between an exposure (vaccine), and whether or not it affects the outcome (disease) being studied....this is called a “retrospective” cohort study (Gordis, p. 170).


What does it all mean?!

Several kinds of studies were used in the meta-analysis, and these studies ranged in sizes & methods. Additionally, they were done in many different countries (although they were primarily European, or in countries with a higher proportion of people of European descent (Australia, U.S.).  This can mean that the study’s results can be generalized to broader populations and cultures.
What did they find?
When looking at multiple studies, comparisons are made of results. If several studies are seen to have similar (or heterogeneous) results, it is seen as a good indicator that the result (disease, health state, or desired outcome) is indeed related to the exposure.

The comparison of the studies in this meta-analysis found that following the Mediterranean Diet did not significantly consistently affect the following things:
Waist circumference measurements, blood pressure measurements

Adopting the Mediterranean Diet did significantly affect:
Lowered triglyceride levels (this is a type of blood fat that you want lower), increased HDL levels (this is a type of blood fat you want higher), decreased fasting blood glucose levels (this is good, as a high fasting blood sugar is an indicator of diabetes & increasing insulin resistance), and insulin resistance was reduced. 

What Caused Confusion? Some of the studies combined the diet with other factors, such as exercise. The studies varied greatly in length. And the studies in the Mediterranean countries showed improvement in all health indicators significantly, except waist circumference. So, if your ancestors ate lots of olives, it is not too surprising that your own body responds well to them too (you still carry their DNA!)....
So, Does it Help, or What?!
Overall, the Mediterranean Diet appears to be associated with lower rates of Metabolic Syndrome, and its development, as several key risk factors are improved by following the diet.
Since Metabolic Syndrome is an increasing public health problem, adopting the Mediterranean dietary habits can be an cost-effective intervention & prevention tool.