mediterranean diet review

It is typically well-known that a Mediterranean diet is associated with a healthier lifestyle, and studies have consistently demonstrated a reduction in mortality, chronic diseases, and cardiovascular diseases linked with a Mediterranean diet. Here we review Mediterranean diet health benefits you might not know about.

Mediterranean diet and improved cognitive function

There are currently no effective drugs to either treat or prevent dementia. One study set out to investigate whether simple dietary changes can affect cognitive function.1

Dietary changes have the advantage of being easy to implement and relatively inexpensive. Dietary changes have the potential to be used as a prevention strategy, at a stage where disease symptoms may not yet be present, potentially delaying onset of symptoms.

The study, published in the Journal of the American Medical Association, extended the emerging evidence that dietary components can have positive effects on brain health. The researchers assessed whether including nuts or olive oil, in addition to sticking to a Mediterranean diet, would have positive outcomes in terms of cognitive changes in older people.

The study population was made up of a sub-cohort of patients from the ‘PREDIMED’ randomized clinical trial. A total of 446 healthy volunteers were randomly assigned to either Mediterranean diet supplemented with 1 litre of olive oil per week, Mediterranean diet supplemented with 30g of mixed nuts per day, or a control group who were advised to reduce their total fat intake. Participants with an average age of 67 years were monitored over a period of four years.

The participants underwent neuropsychological testing at the beginning of the study, and at approximately four years after the study began. These tests measured cognitive change over time.

The study reported a significant improvement in cognitive function in participants allocated to the Mediterranean diet compared with the control group. There was greater memory preservation seen in patients who were eating a Mediterranean diet plus nuts compared with the other two groups.  

The people eating a Mediterranean diet plus olive oil had an overall improvement in frontal function and cognition. The results of the study were found to be independent of age, sex, total energy intake, and vascular risk factors. The benefits were seen even in participants with higher genetic risk of cognitive disorders and dementia.

The authors suggest that the beneficial effects seen are likely due to the antioxidant and anti-inflammatory effects of the phenols found in olive oil and nuts. They suggest that the phenols could potentially reduce the oxidative stress within the brain that leads to neurodegeneration and ultimately the onset of dementia. They also suggest that the benefits may occur through increased blood flow to the brain, which is also promoted by the phenols in olive oil and nuts. Since studies have pointed to a link between vascular risk factors and dementia, this vascular improvement could prevent or delay the onset of cognitive decline.

Overall, the study demonstrated a reduction in age-related cognitive decline in participants who were adhering to a Mediterranean diet supplemented with olive oil or nuts. They suggest that this diet can be a potential prevention strategy, however that further research is necessary.

Mediterranean diet linked with preserved brain connectivity

While the Mediterranean diet has been linked with a lower risk of Alzheimer’s disease, there has been very little research into the mechanisms that may account for these benefits.

Researchers from Bordeaux, France, investigated the potential mechanisms that might be involved in the reduced risk of Alzheimer’s disease. A total of 146 participants were recruited for the study.2 Each participant answered questionnaires, in addition to having an MRI performed to assess brain structure up to 10 years later.

The study reported that adherence to a Mediterranean diet was associated with preservation of white matter microstructure in the brain. In addition, there were increases in structural connectivity within the brain, which were associated with cognitive benefits. These cognitive benefits were estimated to have the equivalence of up to a 10-year delay in cognitive aging.

The researchers suggest that overall quality of the diet, rather than individual foods, more likely explains the benefits observed in the study. In addition, they suggest that the study provides evidence that healthy diets, such as the Mediterranean diet, can have a marked effect on brain structure, in particular structural connectivity.

This connectivity has been linked with cognitive deficiencies seen in the aging brain. The researchers state that this study establishes a link between the Mediterranean diet and preservation of structural integrity as a mechanism for the observed benefits of the Mediterranean diet on risk of cognitive decline.

Mediterranean diet may protect against melanoma

Researchers from northern Italy aimed to extend previous laboratory and epidemiologic research that suggests a role for diet in melanoma risk. Previous research in laboratory animals has suggested that antioxidants could provide protection against melanoma. In addition, the Mediterranean diet has been suggested as beneficial, since incidence of melanoma is relatively low in Italy, Greece, and Albania.

Four types of diets were evaluated in the study,3 from each diet a ‘quality index’ was calculated. These included the Healthy Eating Index 2010 (HEI-2010), Dietary Approaches to Stop Hypertension (DASH) Index, Greek Mediterranean Index (GMI), and Italian Mediterranean Index (IMI). A total of 380 participants in Northern Italy were evaluated for diet and melanoma risk.

The study reported an inverse association between risk of melanoma and the HEI-2010 and the DASH index, but neither of the Mediterranean diet indices. The results suggest that risk of melanoma decreases as diet quality increases (particularly for HEI-201, and DASH).

While there is mounting evidence for the role of dietary factors in many other cancers, melanoma has not typically been associated with diet. Contrary to currently held ideas regarding the risk of melanoma, the results of the current study suggest a role for dietary factors.

The association was found to be strongest in women, in particular young women. While there appear to be gender-specific differences, the researchers state that the reasons for these differences are unknown. They do suggest, however that hormonal factors could play a role, given the fact that younger (premenopausal) women seem to have had the greatest reduction in risk with increasing diet quality. The researchers suggest further study to confirm and extend the relationship between diet and gender differences in melanoma risk.

Mediterranean diet and breast cancer risk 

A study published in the Journal of the American Medical Association Internal Medicine, reported that sticking to a Mediterranean diet could help to reduce the risk of developing breast cancer.4

The study was conducted as a part of the PREDIMED trial, which is a randomised controlled trial that was carried out in Spain between 2003-2009, including over 4000 women between the ages of 60 and 80 years. The women were assigned to either a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with nuts, or a reduced-fat diet, as a control group.

The study reported that rate of breast cancer in the Mediterranean diet plus olive oil group was reduced, as was the rate of breast cancer in the Mediterranean diet plus nuts group, compared with the control group.

The greatest reduction in risk was seen in participants who were eating a Mediterranean diet that was supplemented with olive oil, which showed a 62% reduction in risk of malignant breast cancer. While there was a reduction in risk with the Mediterranean diet plus nuts group, the effect was not significant.

The researchers report that this is the first study to show a preventive effect of diet on the incidence of breast cancer, and that a Mediterranean diet with extra virgin olive oil may have the potential to be a primary prevention measure for breast cancer. 

Mediterranean diet and brain volume

In a study investigating the effects of a Mediterranean diet on measured brain volume and cortical thickness, researchers used MRI to measure brain structure in over 650 elderly people without dementia.5

Dietary intake was also assessed, and scored between 0-9 for association with a Mediterranean diet. The study reported that sticking more closely to a Mediterranean diet was associated with greater total brain volume, total gray matter volume, and total white matter volume.

The study also reported that a higher amount of fish consumption, and lower amount of meat consumption, were associated with larger total gray matter volume.

The researchers concluded that a Mediterranean diet was associated with a reduction in brain atrophy (shrinkage), which was estimated as an equivalent of five years of aging. Eating more fish and less meat appear to be key contributors to this effect.

Mediterranean diet and longevity

A study,6 reported in the British Medical Journal, assessed the association between a Mediterranean diet and telomere length. Telomeres are, in essence, protective barriers present as repetitive DNA sequences at the ends of chromosomes. Over time, telomeres become shorter, a process that is enhanced by inflammation and oxidative stress. Studies have demonstrated links between telomere length and aging, with a shorter telomere length being linked with a reduction in life expectancy. Telomeres, therefore, are regarded as a biomarker of aging.

The study was based on the idea that telomere deterioration may be modifiable, likely by lifestyle and dietary factors. The study set out to assess the effect of consuming a Mediterranean diet on telomere length. The idea of the study was based on the fact that components of the Mediterranean diet (such as fruits, vegetables, and nuts) have anti-oxidant and anti-inflammatory activities.

The study assessed the association between the Mediterranean diet and telomere length in women from the Nurses’ Health Study Cohort in the United States. As a subset of the original cohort, 4676 female registered nurses, from 11 US states, aged between 30 and 55 years were included in the study.

The study revealed that eating a Mediterranean diet was significantly associated with longer telomere length. The greatest association was seen in women who stuck more closely to a Mediterranean diet. According to the researchers, the differences seen would correspond to an average of 4.5 years of aging.

References:

1. Valls-Pedret, C, Sala-Vila, A, Serra-Mir, M, Corella, D, de la Torre, R, Martínez-González, MA, Martínez-Lapiscina, EH, Fitó, M, Pérez-Heras, A, Salas-Salvadó, J, Estruch, R, Ros, E. “Mediterranean Diet and Age-Related Cognitive Decline :  A Randomized Clinical Trial” JAMA Intern Med. Published online May 11, 2015.

2. Pelletier, A, Barul, C, Féart, C, Helmer, C, Bernard, C, Periot, O, Bilharreguy, B, Dartigues, J-F, Allard, M, Barberger-Gateau, P, Catheline, G , Samieri, C. “Mediterranean diet and preserved brain structural connectivity in older subjects” Alzheimer’s & Dementia, Published Online: July 16, 2015

3. Malagoli, C, Malavolti, M, Agnoli, C, Crespi, CM, Fiorentini, C, Farnetani, F, Longo, C, Ricci, C, Albertini, G, Lanzoni, A, Veneziano, L, Virgili, A, Pagliarello, C, Santini, M, Fanti, PA, Dika, E, Sieri, S, Krogh, V, Pellacani, G, Vinceti, M. “Diet Quality and Risk of Melanoma in an Italian Population” J. Nutr. August 1, 2015 vol. 145 no. 8 1800-1807

4. “Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial:  A Randomized Clinical Trial” JAMA Intern Med. Published online September 14, 2015. doi:10.1001/jamainternmed.2015.4838 

5. Gu Y, Brickman AM, Stern Y, Habeck CG, Razlighi QR, Luchsinger JA, Manly JJ, Schupf N, Mayeux R, Scarmeas N. “Mediterranean diet and brain structure in a multiethnic elderly cohort.” Neurology. 2015 Oct 21.

6. Crous-Bou, M, Fung, TT, Prescott, J, Julin, B, Du, M, Sun, Q, Rexrode, KM, Hu, FB, De Vivo, I. “Mediterranean diet and telomere length in Nurses’ Health Study: population based cohort study”BMJ 2014;349:g6674

Image by DanaTentis from Pixabay 

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