Mediterranean diet linked to richer gut diversity, study finds

By Priyanjana Pramanik, MSc.Reviewed by Susha Cheriyedath, M.Sc.Mar 12 2024

In a recent study published in the journal Nutrients, researchers explored how following the Mediterranean diet (MD) influences the gut microbiome of healthy individuals through a well-defined cohort study.

Their results indicate that adhering to MD increases the species diversity of microbiota, offering insights into how it can lead to measurable health benefits.

Study: Impact of the Mediterranean Diet on the Gut Microbiome of a Well-Defined Cohort of Healthy Individuals. Image Credit: Marian Weyo / Shutterstock

Background

Traditionally followed by many Mediterranean coastal communities, MD is a nutrient-rich diet dominated by whole grains, healthy fats, fruits, and vegetables with antioxidant and anti-inflammatory properties.

It has been associated with improved cardiovascular health and reductions in the risk of metabolic syndrome, neurogenerative disorders, type 2 diabetes, and some cancers. This is in contrast with diets high in refined carbohydrates and fats, which have been implicated in increases in obesity and multiple metabolic disorders.

The effect of different diets may be mediated by how they influence the gut microbiome, which plays a crucial role in disease prevention and maintaining health. Certain dietary habits and food components associated with MD may strengthen beneficial gut microbiota, as dietary diversity, fat composition, and fiber intake all leave distinct marks on microbial communities.

About the study

In this study, researchers recruited healthy volunteers (donors and relatives) from a fecal transplant clinic in Spain. Participating individuals had a body mass index (BMI) between 17 and 30, no known diseases or disorders, did not drink more than 50g of alcohol per day, and had not taken vaccines and specified medications in the three months preceding the study.

Participants were stratified by age and provided demographic information, dietary intake through a food-frequency questionnaire, and medical history. Their adherence to the MD was assessed using a dietary quality index; those receiving a score of 1-4 were classified as having ‘good’ adherence, while those scoring 5-9 had ‘medium’ adherence.

The gut microbiome was assessed by analyzing stool samples, identifying microbe species, and measuring species richness, the number of species found in a sample, and species evenness (Pielou index), which measures uniformity or similarity in the abundance of different species.

The inverse Simpson index was used to indicate richness in communities with the same evenness, while the Shannon index examined how many species lived in a given habitat and their relative abundances.

The alpha diversity, which measures species diversity within a single individual, and beta diversity, which assesses diversity differences among individuals, were also calculated. Researchers also calculated correlations between microbial abundance and nutrient intake.

Findings

Of the 60 individuals enrolled in the study, slightly over 50% were female, and the median age was 31. On average, females showed more species richness and higher values for the Pielou, inverse Simpson, and Shannon indexes.

Firmicutes, Bacteroidetes, and Actinobacteria, were the dominant phyla in males and females. Abundant genera included Bifidobacterium, Bacteroides, Faecalibacterium, Prevotella, and Blautia. While Bacteroides were abundant across all age groups, Bifidobacterium became less dominant with age.

Across all diversity indices, children showed consistently lower values than other groups. Teenagers had the highest richness values, while older adults (49 years old and above) had higher Pielou, Shannon, and inverse Simpson values. Stratifying these results by sex showed that these differences remained for males but not females, except for species evenness, which persisted for both.

The median diet adherence score for the 39 individuals who completed the food-frequency questionnaires was 5. People with good adherence had a median age of 48, while those with medium adherence were younger, with a median age of 30.

Better MD adherence was associated with having higher Bacteroides and Paraprevotella abundance, but there were no sex-based differences in alpha and beta diversity indices. Stratifying by age, the researchers found that good adherence decreased the abundance of different genera for different groups.

Correlation analysis showed that fat intake was negatively associated with the Shannon index, while non-starch polysaccharides (NSPs) and total sugars were positively associated. The Pielou index showed a negative association with red meat intake while directly correlating with total sugars and NSPs.

People with better adherence also showed differences in pathways related to bladder cancer, polycyclic aromatic hydrocarbon degradation, and vasopressin-regulated water reabsorption. They showed more enzymes related to lipid metabolism and different biosynthesis processes.

Conclusions

This study assessed MD influence on gut microbiota through a well-defined cohort based on sex and age, finding significant differences in microbial composition as well as alpha and beta diversity associated with adherence. These findings were strengthened by the identification of functional pathways and specific bacterial taxa that differed based on adherence levels.

The small sample study size may limit the generalizability of these findings; further studies using longitudinal designs and larger cohorts are needed to better understand how MD can strengthen the microbiome and boost health outcomes.