Davis CR, Hodgson JM, Woodman R, Bryan J, Wilson C, Murphy KJ. A Mediterranean diet lowers blood pressure and improves endothelial function: results from the MedLey randomized intervention trial. Am J Clin Nutr. 2017;105(6):1305-1313.
MedLey was a 6-month, randomised controlled 2-cohort parallel group intervention trial; participants were assessed at baseline, 3 months, and 6 months.
One hundred sixty-six healthy Australian men and women aged 65 years and above with normal cognitive function and English language proficiency, recruited from metropolitan Adelaide, South Australia
Study Medication and Dosage
Participants randomly allocated to the experimental group were required to maintain an intervention dietary pattern based on the traditional Cretan MedDiet (ie, vegetables, fruits, olive oil, legumes, fish, whole grain cereals, nuts, and seeds with low consumption of processed foods, dairy products, red meat, and vegetable oils) for 6 months. Those allocated to the control group were asked to maintain their customary lifestyle and diet.
Data from these cohorts have informed several recent publications evaluating the impact of the Mediterranean diet on cognitive function, F2-isoprostanes, and triglycerides. This current study used blood pressure measurements taken on 5 consecutive days at baseline, 3 months, and 6 months. Endothelial function was assessed by flow-mediated dilation (FMD) at baseline and at 6 months. Adherence to Mediterranean diet was monitored through 3-day food records.
Participants in the Mediterranean-style diet group had significantly lower systolic blood pressure at 3 months (mean: −1.3 mm Hg [95% CI: −2.2, −0.3 mm Hg; P=0.008]) and at 6 months (mean: −1.1 mm Hg [95% CI: −2.0, −0.1 mm Hg; P=0.03]) and a 1.3% higher FMD (95% CI: 0.2%, 2.4%; P=0.026) at 6 months, compared to baseline. These results show a significant improvement in endothelial function and a small but significant reduction in systolic blood pressure in the Mediterranean diet group.
While we know greater adherence to a Mediterranean diet provides health benefits, we must add the qualifier: The majority of data substantiating these claims comes from studies conducted on cohorts of participants who live in the Mediterranean region. The question now being addressed by researchers is whether these benefits might be transposed to other parts of the world, in this case Australia.
This current paper by Karen Murphy’s team is one of a series derived from the MedLey Cohort recruited from metropolitan Adelaide, South Australia. The initial focus of the trial was to determine if greater Mediterranean diet adherence would be associated with either improved cognitive function or greater psychological well-being.1 Past prospective studies report higher adherence to a Mediterranean diet is associated with improvements in a range of cognitive outcomes in healthy older adults, including slower global cognitive decline,2-4 higher episodic memory and global cognitive performance,5,6 and higher verbal memory performance.7 The results of this initial analysis were published in September 2016; unfortunately, they did not show that the active dietary intervention had a significant impact on cognitive function or psychological health.8
Normal Australian diets may be too pro-inflammatory and too pro-oxidative. It may take longer than 6 months to erase a lifetime of brain damage.
On the other hand, this current paper and a second paper published by the same authors in July 2017 suggest that the intervention will have an impact on cardiovascular disease (CVD). As mentioned, the Mediterranean diet appears to have a small but significant effect on blood pressure and endothelial function. The July paper reported reductions in F2-isoprostanes and triglycerides, both actions that should be associated with lower CVD risk.9
It is unclear why dietary intervention had no impact on cognitive parameters in the earlier study. Admittedly there is no clear mechanistic explanation for why following a Mediterranean diet improves cognitive function. The assumption has been that this dietary pattern supplies specific nutrients (ie, vitamins E, B6, B12, folate, monounsaturated fatty acids, fish, carotenoids, flavonoids, antioxidants, and omega-3 and omega-6 polyunsaturated fatty acids) that may protect against cognitive decline.10 It has been assumed that combining the various food elements found in this diet would have some sort of synergistic or at least additive action on the brain, and that the effects could not be attributed to a single food.
These results question this assumption. Perhaps there is a key chemical constituent found in Mediterranean olive oil not present in the Australian iteration? Perhaps it is not the general pattern but large amounts of specific foods suggested in the PrediMed trials that supplied participants with extra virgin olive oil (EVOO) or nuts?11 In that Spanish trial participants received about 2 ounces of EVOO per day.
It is also possible that the Mediterranean diet is good for health, but the standard Western diet is so detrimental that participants who followed this experimental diet were simply avoiding the deleterious aspects of their regular diet.12 Normal Australian diets certainly might be considered too proinflammatory and too pro-oxidative to see a quick fix via diet.13 It may take longer than 6 months to erase a lifetime of brain damage. The MedLey study does not detail actual mean consumption by weight or servings of specific foods. Perhaps there is a minimum quantity of EVOO or nuts needed to have significant impact?
A recently published (August 2017) study reports cognitive benefits of Mediterranean dietary adherence in a Greek cohort of 1,865 older adults. Analysis of data from the Hellenic Longitudinal Investigation of Ageing and Diet (HELIAD) showed that for each unit increase in the Mediterranean dietary score (MedDietScore) there was a 10% decrease in odds for dementia.14
We end up having to rely on terms such as “multifactorial factors” to explain the inconsistent results. When we compare the findings to date from the MedLey cohort to findings from previous studies, the question arises: Does the Mediterranean diet offer less protection to people in Australia than to people in other parts of the world?
Is there something unique about living in Australia?