Newswise — Eating a Mediterranean diet can slow down cognitive decline.
The Mediterranean diet can improve your mind, as well your heart, shows a study published in the open-access journal Frontiers in Nutrition.
By sticking to the Mediterranean diet the study showed that people had slowed rates of cognitive decline, reduced conversion to Alzheimer’s, and improved cognitive function.
The main foods in the Mediterranean diet (MedDiet) include plant foods, such as leafy greens, fresh fruit and vegetables, cereals, beans, seeds, nuts, and legumes. The MedDiet is also low in dairy, has minimal red meat, and uses olive oil as its major source of fat.
Leading author Roy Hardman from the Centre for Human Psychopharmacology Swinburne University of Technology Melbourne Australia and his colleagues evaluated all the available papers between 2000-2015 that investigated if and how a MedDiet may impact cognitive processes over time. In total, 18 out of the 135 articles met their strict inclusion criteria.
“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;” he said.
Attention, memory, and language improved. Memory, in particular, was positively affected by the MedDiet including improvements in: delayed recognition, long-term, and working memory, executive function, and visual constructs.
“Why is a higher adherence to the MedDiet related to slowing down the rate of cognitive decline? The MedDiet offers the opportunity to change some of the modifiable risk factors,” he explained.
“These include reducing inflammatory responses, increasing micronutrients, improving vitamin and mineral imbalances, changing lipid profiles by using olive oils as the main source of dietary fats, maintaining weight and potentially reducing obesity, improving polyphenols in the blood, improving cellular energy metabolism and maybe changing the gut micro-biota, although this has not been examined to a larger extent yet.”
Moreover, the benefits to cognition afforded by the MedDiet were not exclusive to older individuals. Two of the included studies focused on younger adults and they both found improvements in cognition using computerized assessments.
The researchers stress that research in this area is important due to the expected extensive population aging over the next 20-30 years. They envision that the utilization of a dietary pattern, such as the MedDiet, will be an essential tool to maintain quality of life and reduce the potential social and economic burdens of manifested cognitive declines like dementia.
“I would therefore recommend people to try to adhere or switch to a MedDiet, even at an older age,” Hardman added.
Like many researchers, Hardman takes his research home: “I follow the diet patterns and do not eat any red meats, chicken or pork. I have fish two-three times per week and adhere to a Mediterranean style of eating.”
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.
Systematic, Criteria-Driven
As always, encouraging news outlets covering medicine to practice journalism, not stenography. https://twitter.com/garyschwitzer/status/1267796903141539846
Thanks @garyschwitzer & @HealthNewsRevu
So helpful & rational as always:
"Often it is what journalists allow interviewees to say – unchallenged – that is most concerning" https://twitter.com/garyschwitzer/status/1267796903141539846
CBS @60Minutes promoted one hospital’s “promise of plasma” for #COVID19. Here are some things that you need to know about that story. https://www.healthnewsreview.org/2020/06/60-minutes-promotes-one-hospitals-promise-of-plasma/
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