The Mediterranean Diet in Australia

Relation

Davis CR, Hodgson JM, Woodman R, Bryan J, Wilson C, Murphy KJ. A Mediterranean diet lowers blood pressure and improves endothelial function: results of the MedLey randomized intervention trial.Am J Clin Nutr. 2017;105(6):1305-1313.

Draft

MedLey was a 6-month, randomized, controlled, parallel-group intervention study with 2 cohorts; Participants were assessed at baseline, 3 months, and 6 months.

Participant

One hundred and sixty-six healthy Australian men and women aged 65 years and over with normal cognitive function and English proficiency recruited from metropolitan Adelaide, South Australia

Study medication and dosage

Participants randomly assigned to the experimental group were required to maintain an intervention diet regimen based on the traditional Cretan MedDiet (i.e. vegetables, fruits, olive oil, legumes, fish, whole grains, nuts and seeds with low consumption of processed foods). dairy products, red meat and vegetable oils) for 6 months. Those assigned to the control group were asked to maintain their usual lifestyle and diet.

Target parameters

Data from these cohorts have influenced several recent publications evaluating the effects 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 dilatation (FMD) at baseline and 6 months. Adherence to the Mediterranean diet was monitored through 3-day dietary records.

Key insights

Participants in the Mediterranean diet group had significantly lower systolic blood pressure after 3 months (mean: -1.3 mm Hg [95% CI: −2.2, −0.3 mm Hg;P=0.008]) and after 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) after 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.

Practice implications

Although we know that greater adherence to a Mediterranean diet provides health benefits, we must add the caveat: The majority of data supporting these claims comes from studies conducted on cohorts of participants living in the Mediterranean region. The question researchers are now addressing is whether these benefits could be transferred to other parts of the world, in this case Australia.

This recent paper from Karen Murphy's team is one of a series drawn from the MedLey cohort recruited from metropolitan Adelaide, South Australia. The initial focus of the study was to determine whether greater adherence to the Mediterranean diet would be associated with either improved cognitive function or greater psychological well-being.¹Previous prospective studies report that 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,^2-4higher episodic memory and global cognitive performance,^5.6and higher verbal memory performance.⁷The results of this initial analysis were published in September 2016; Unfortunately, they did not show that the active nutritional intervention had a significant impact on cognitive function or mental health.⁸

Normal Australian diet can be too pro-inflammatory and too pro-oxidant. It can take longer than 6 months to reverse lifelong brain damage.

On the other hand, this current study and a second study published by the same authors in July 2017 suggest that the intervention will have an impact on cardiovascular disease (CVD). As previously mentioned, the Mediterranean diet appears to have a small but significant impact on blood pressure and endothelial function. The July paper reported reductions in F2-isoprostanes and triglycerides, both effects that should be associated with a lower risk of CVD.⁹

It is unclear why the dietary intervention had no effect on cognitive parameters in the previous study. Admittedly, there is no clear mechanistic explanation as to why a Mediterranean diet improves cognitive function. This dietary pattern has been hypothesized to provide certain nutrients (i.e., vitamins E, B6, B12, folic acid, monounsaturated fatty acids, fish, carotenoids, flavonoids, antioxidants, and omega-3 and omega-6 polyunsaturated fatty acids) that may protect against cognitive decline.¹⁰It was believed that the combination of the different food elements found in this diet would have some kind of synergistic or at least additive effect on the brain and that the effects could not be attributed to a single food.

These results challenge this assumption. Perhaps there is an important chemical component in Mediterranean olive oil that is not present in the Australian iteration? Maybe it's not the general pattern, but large amounts of specific foods suggested in the PrediMed studies that provided participants with extra virgin olive oil (EVOO) or nuts?¹¹In this Spanish study, participants were given 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 harmful that the participants who followed this experimental diet simply avoided the harmful aspects of their regular diet.¹²Normal Australian diets could certainly be considered too pro-inflammatory and too pro-oxidant to see a quick fix through diet.¹³It can take longer than 6 months to reverse lifelong brain damage. The MedLey study does not provide information on actual average consumption by weight or portions of specific foods. Perhaps a minimum amount of EVOO or nuts is required to have a significant effect?

A recently published (August 2017) study reported cognitive benefits of a Mediterranean diet in a Greek cohort of 1,865 older adults. Analysis of data from the Hellenic Longitudinal Investigation of Aging and Diet (HELIAD) showed that for every 10% increase in the Mediterranean Diet Score (MedDietScore), the likelihood of dementia decreased.¹⁴

In the end, we have to rely on terms like “multifactorial factors” to explain the contradictory results. Comparing the findings so far from the MedLey cohort with 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 anything unique about living in Australia?