A review of a small number of studies examining impacts of the Mediterranean Diet finds that the diet is associated with both cognitive improvements and slower cognitive decline. The study is laudable in that it seeks to capture a bit of the “big picture” by examining the results of many studies, and focusing on 18 studies that met the researchers’ criteria for inclusion.
The challenges of pinning down the effects of diet are well known (see, for example, a recent article in the New York Times reflecting on these issues) so determining the actual benefits of the Mediterranean diet will take time and careful analysis. This news release is far more convinced of that linkage than is warranted.
We assume that diet and exercise help us maintain health and longevity, and we may be right. But determining cause and effect in this arena is elusive.
Because cognitive decline and dementia are increasing in prevalence as the population lives longer, any lifestyle measures that delay or mitigate this are important to learn about and implement.
Although the text clearly identifies the components of the Mediterranean diet, it does not attempt to “cost” them out for the typical American. The costs of adhering to a Mediterranean diet could be prohibitive, especially for older adults living on fixed incomes. While it would be some work to estimate the annual cost of eating this way for a person or family, the cost consideration could at least be acknowledged.
The release mentions three outcomes—“slowed rates of cognitive decline, reduced conversion to Alzheimer’s, and improved cognitive function”—and explains those outcomes a bit more specifically lower in the text. But missing from the text is information supporting the benefit claims. Slower than what? Reduced relative to what? Improved relative to what? Our criteria call for releases to report the risk reduction in absolute terms if at all possible, but this release gives no numbers at all.
There appear to be minimal to no health debits stemming from the Mediterranean diet, assuming one eats in moderation.
This is a tough call. The release makes clear that the scientists conducting this analysis used “strict inclusion criteria” to cull 18 studies from a group of 135 for examination. Identifying the size of the sample is good, as it gives reporters the opportunity to evaluate that. But the release tells you nothing about those inclusion criteria. It turns out that the authors did a fairly rigorous job of choosing trials that were longitudinal in nature, including those that examine the same cohorts repeatedly over time, and they also excluded studies exploring outcomes other than cognitive decline/improvement, their dependent variables of choice. However, the number “18” should send up red flags for any journalist. The analytical strategy used in this study employed the study as the unit of analysis, so the sample size is actually 18. That’s way too small for purposes of generalization.
Finally, because the published review of studies included observational studies, we rate this not satisfactory for not addressing the lack of cause and effect. Further, the release uses active verbs to describe the benefit when cause isn’t shown, such as in the headline: “Eating a Mediterranean diet can slow down cognitive decline.”
The issues identified in this study are real ones for all individuals, particularly older ones. This is an important population health problem.
Although the published study indicates that none of the principal investigators received funding to conduct this study, presumably minimizing conflicts of interest, the news release doesn’t address these issues. That’s unfortunate, since the investigators’ independence would be a strength of the study.
Other lifestyle or medical interventions are not mentioned in the release. The published review article itself cited other lifestyle interventions.
The ingredients of the Mediterranean Diet are available worldwide.
Studies of this diet are numerous. Although this meta-analysis may be unique in its analytical characteristics, the text makes no claim for novelty.
The release includes quotes which make the study sound like new information, when it really isn’t. For example:
“The most surprising result was that the positive effects were found in countries around the whole world. So regardless of being located outside of what is considered the Mediterranean region, the positive cognitive effects of a higher adherence to a MedDiet were similar in all evaluated papers.”
The researcher quoted in the news release recommends that folks adopt the Mediterranean Diet and testifies that he himself follows it. That is a fairly robust statement of advocacy, but it is not overly sensational.