Author: Leanne Mitchell, APD

3 July 2020

 

Microba’s Accredited Practising Dietitian and Microbiome Coach, Leanne Mitchell, summarises the latest studies exploring the connection between the Mediterranean Diet and the gut microbiome.

 

What we know

1. The Mediterranean Diet (Med Diet) has long been linked to healthy living and ageing. This dietary pattern is characterised by a varied intake of prebiotic fibre from vegetables, fruits, legumes, nuts and whole grains and low intakes of refined grains and saturated fat sources (from dairy and meat products).
2. Prebiotic fibres fuel beneficial bacteria with anti-inflammatory metabolites. A varied intake of these fibre types supports a diverse, health-promoting gut microbiome.
3. A health-promoting gut microbiome and the Med Diet are both associated with a reduced risk of cardiovascular disease, type II diabetes, obesity, inflammatory conditions, neurodegenerative disease and cancer.

These insights allow us to infer that the beneficial effects of the Med Diet may be mediated by the gut microbiome. To date, however, most of the health benefits noted from a Med Diet were based on observational studies or interventional studies without analysis of the gut microbiome.

 

What is new?

Recently two randomised controlled trials (RCT) published results of gut microbial alterations following a Med Diet intervention.

The first study by Meslier and colleagues¹ was conducted in overweight and obese adults who were otherwise healthy.  Participants were either randomised to MedDiet (without energy/calorie reduction) or a controlled diet (regular/usual).  The results indicate that a Med Diet:

• Increased levels of fibre-degrading species and decreased levels of species associated with inflammation.
• Increased gene richness (diversity) in those with reduced inflammatory markers.
• Decreased insulin resistance and stool bile acid levels; these changes were dependant on the baseline levels and variations of the species involved in these pathways.
• Reduced blood cholesterol levels (total, LDL and HDL).

The second study investigated if a one-year Med Diet could alter the gut microbiome and reduce frailty. Ghosh and colleagues² profiled 612 non-frail or pre-frail older adults from five European countries. Participants were randomly assigned to either a Med Diet or a controlled diet (regular diet with dietary education).  The results found:

• Med Diet modulated the gut microbiome in a manner associated with reduced frailty, improved cognitive function and reduced inflammation.
• Adherence to the Med Diet was associated with a reduced loss of microbiome diversity that is often seen in ageing.
• Inferred analysis found that Med Diet-associated microbial shifts increased the potential to produce SCFAs and lowers the potential to produce BCAAs, secondary bile acids, p-cresol, ethanol and carbon dioxide.
• Analysis of bacterial clusters found that the bacteria enriched by the Med Diet occupy keystone interaction positions, whereas frailty-associated bacteria are peripheral in the networks.

 

What does it mean?

These studies provide some of the first evidence that the health benefits of the Med Diet could be, in part, linked to positive changes in the gut microbiome.  Findings indicate that the Med Diet can improve or stabilise diversity, but most importantly can also change the composition of the gut microbiome, increasing the abundance of beneficial and keystone species. These studies suggest that these microbiota shifts can support health benefits such as reduced inflammation, improved metabolic biomarkers (cholesterol and insulin sensitivity) and reduced frailty (healthy ageing).

Therefore, the Med Diet is an attractive intervention in the management of those with (or at risk of) metabolic disease/s and to support healthier ageing.  However, the key to successful dietary intervention is personalisation.  Potential issues of cost, availability and cooking skills should be considered when prescribing the Med Diet to clients.  For those with food allergies/sensitivities, certain medical conditions or functional gastrointestinal disorders, support from a healthcare professional with accredited skills in managing these comorbid conditions is required.

 

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