In 2003, 16 Spanish research groups began a long-term study designed to uncover the effects of the Mediterranean diet on preventing cardiovascular disease (CVD) in people at high risk of the condition. Known as the PREDIMED study, it ran until 2011, studying nearly 7400 older adults at high risk of developing CVD.
The findings of this and other studies of the Mediterranean diet have been significant, with positive outcomes for cardiovascular health identified, along with a host of other benefits for weight management, diabetes, metabolic syndrome and mental health.
Attendees of the 2017 Australian Nut Conference were fortunate to hear from two esteemed researchers with extensive knowledge of the health benefits of the diet.
Professor of Nutrition and Bromatology Jordi Sals-Salvado from the Department of Biochemistry and Biotechnology at Spain’s Universitat Rovira I Virgili provided global insights from the PREDIMED study.
Dr Catherine Itsiopoulos, Head of the School of Allied Health at Melbourne’s La Trobe University, and an international leader on Mediterranean diet research, then provided an Australian perspective on the latest nut health research.
Here we take a look at the key research findings on the many health benefits of the Mediterranean diet and zero in on some of the outcomes specific to the inclusion of daily nut consumption in the diet.
What is the Mediterranean diet?
The Mediterranean diet is based on the traditional healthy eating and cooking habits of those countries bordering the Mediterranean Sea.
The diet is based on eating primarily plant-based products including vegetables, fruit, whole grains, legumes, nuts, seeds, herbs and spices. It encourages frequent intake of fish and shellfish, moderate consumption of wine with meals, and low intake of red and processed meat, milk and milk products and simple sugars. Olive oil is encouraged as the main culinary fat.
How PREDIMED was conducted
The study’s 7400 subjects, 55-80 year old men and 60-80 year old women, were randomised into three groups: the low-fat control diet, the Mediterranean diet supplemented with virgin olive oil, and the Mediterranean diet supplemented with 30 grams of tree nuts.
The focus for those on the Mediterranean diets was to introduce changes to their overall food pattern, rather than focusing on particular foods or micronutrients.
A smorgasbord of powerful benefits
The study found the Mediterranean diet supplemented with virgin olive oil or nuts can deliver a host of health benefits related to CVD, diabetes, metabolic syndrome and brain health. These include:
- An anti-inflammatory effect on the cardiovascular system
- Reduced cardiovascular events in people at high cardiovascular risk. This included myocardial infarction, stroke and death from cardiovascular causes.
- Inverse association between following the diet and key CVD risk factors including diabetes, hypertension, dyslipidemia and obesity
- Reduced waist circumference, particularly in people with diabetes
- Reduction in diabetes incidence compared to those following the low fat diet, without any reduction in body weight or increase in physical exercise
- Improved insulin resistance
- Lower prevalence of metabolic syndrome. Metabolic syndrome refers to a set of conditions that often occur together that increase risk of diabetes, stroke and heart disease. These include obesity, high blood pressure, high triglycerides, low levels of HDL (good) cholesterol, and insulin resistance.
- Improved overall brain health and potential to counter-act age-related cognitive decline including Alzheimer’s disease and dementia
- Reversal of fatty liver, which can increase risk for type-2 diabetes and liver cancer
More recently, an Australian study (The SMILES Trial, Jacka, Opie et al 2017) has shown that the Mediterranean diet with olive oil and nuts may offer a powerful means of combating depression.
As Dr Itsiopoulos explained, a study of people suffering from clinical depression saw 32% on the Mediterranean diet experience a remission in depression symptoms, compared to just 8% in the control group receiving standard care with no diet change. The more closely they adhered to a Mediterranean diet, the lower their score for depression and anxiety. These are significant findings.
Nuts: a powerful addition to the Mediterranean diet
The advantages of the Mediterranean diet are significant, however its effects appear to be even more marked when a daily 30-gram serve of nuts is incorporated. The Mediterranean diet plus nuts group in the PREDIMED study displayed some additional long-term health benefits that were not observed in the olive oil or control groups.
Cardiovascular disease
- Reduced levels of tissue factor pathway inhibitor, which inhibits thrombin, a substance that plays a role in the blood clotting process
- Delayed progression of internal carotid intima-media thickness and plaque
- Lower mean plasma glucose levels
- Lower systolic and diastolic blood pressure
- Significantly lower LDL (bad) cholesterol
- Healthier LDL:HDL cholesterol ratio
- Increased fibre intake
- Increased polyunsaturated (good) fat intake
Weight management
- Improved Body Mass Index (BMI)
- Improved waist circumference
- Inverse association between nut consumption and obesity and central obesity
- A lifetime habit of eating 30 grams of nuts 3+ times per week resulted in a 39% reduction in total mortality in an older Mediterranean population at high risk of CVD
Diabetes
- Inverse relationship with diabetes: eating 3+ serves of nuts per week significantly lowers the risk of diabetes, compared to eating one or fewer serves per week
Metabolic syndrome
- Inverse relationship with metabolic syndrome: eating 3+ serves of nuts per week lowers the risk of developing metabolic syndrome, compared to eating one or fewer serves per week
- Potential to reverse metabolic syndrome, in particular, reduced waist circumference
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- Significant association with improved levels of brain-derived neurotrophic factor (BDNF) in people suffering from depression. BDNF is a protein thought to be connected with depression. Higher levels are associated with better brain health.
Never too late to change
The results of the PREDIMED study have had far-reaching effects, and are leading the shift from low-fat dietary advice to guidelines that recommend a high vegetable, high fat diet.
However, improvements in consumer habits are still needed, in Australia at least, with Dr Itsiopoulos highlighting some concerning trends revealed in the 2015 National Health Survey results:
- Australians are eating 30% less fruit and vegetables than they were 15 years ago
- 25% of Australian adults eat no vegetables on an average day, with only 7% eating the recommended five serves per day
- Australians are eating an average of 6 grams of nuts and seeds per day – well short of the recommended 30 grams per day
- 35% of Australians’ energy comes from high fat, high sugar food that adds no value to their diet, such as cakes, biscuits and soft drinks
Dr Itsiopoulos says dealing with that last point alone would be a good place to start. “Wouldn’t it be great if we just replaced our discretionary foods with healthy snacks, like nuts, dried fruit, fresh fruit or yoghurt – foods such as these that are part of a Mediterranean diet,” she said.
On the upside, Professor Sals-Salvado says one of the most important implications of the PREDIMED study’s findings is that it’s never too late to start. “The population of this study was aged from 55 to 80 years, so it is never too late to change dietary habits to improve our health,” he said.
Further details of the PREDIMED study and a full list of references can be found here.
