In a recent study published in the journal Nutrientsresearchers investigated how following a Mediterranean diet (MD) affects the gut microbiome of healthy individuals through a well-defined cohort study.
Their results show that adherence to MD increases the species diversity of the microbiota, offering insight into how it can lead to measurable health benefits.
Study: Effect of the Mediterranean diet on the gut microbiome of a well-defined cohort of healthy subjects. Image credit: Marian Weyo / Shutterstock
Record
Traditionally followed by many Mediterranean coastal communities, the MD is a nutrient-dense 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, neurodegenerative disorders, type 2 diabetes and certain cancers. This is in contrast to diets high in refined carbohydrates and fats, which have been implicated in the rise of obesity and multiple metabolic disorders.
The effect of different diets may be mediated by how they affect the gut microbiome, which plays a key role in preventing disease and maintaining health. Certain dietary habits and food components associated with MD may enhance beneficial gut microbiota, as dietary diversity, fat composition, and fiber intake leave distinct imprints on microbial communities.
About the study
In this study, researchers recruited healthy volunteers (donors and relatives) from a fecal transplant clinic in Spain. Participants had a body mass index (BMI) between 17 and 30, had no known diseases or disorders, did not drink more than 50 grams of alcohol per day, and had not received vaccines or specific medications in the three months preceding the study.
Participants were stratified by age and provided demographic information, dietary intake via a food frequency questionnaire, and medical history. Their MD compliance was assessed using a diet quality index. Those who received a score of 1-4 were classified as having “good” compliance, while those who scored 5-9 had “moderate” compliance.
The gut microbiome was assessed by analyzing stool samples, identifying microbial species, and measuring species richness, the number of species found in a sample, and species evenness (Pielou index), which measures the uniformity or similarity in abundance of different species.
The inverse Simpson index was used to indicate richness in communities with evenness, while the Shannon index looked at how many species lived in a given habitat and their relative abundance.
Alpha diversity, which measures species diversity within a single individual, and beta diversity, which assesses diversity differences between individuals, were also calculated. The researchers also calculated correlations between microbial abundance and nutrient uptake.
Foundings
Of the 60 subjects in the study, just over 50% were female and the median age was 31. On average, females showed more species richness and higher values for the Pielou, reverse Simpson and Shannon indices.
Firmicutes, Bacteroidetes and Actinobacteria were the dominant flora in males and females. Abundant genera are included Bifidobacterium, Bacteroides, Feces, Prevotellaand Deliciousness. While Bacteroides were abundant in all age groups, Bifidobacterium became less dominant with age.
In all indicators of diversity, children consistently showed lower values than other groups. Teenagers had the highest richness values, while older adults (49 years and older) had higher Pielou, Shannon, and reverse Simpson values. Stratifying these results by gender showed that these differences persisted for males but not females, except for species uniformity, which persisted for both.
The median dietary compliance score for the 39 subjects who completed food frequency questionnaires was 5. Subjects with good adherence had a median age of 48, while subjects with moderate adherence were younger, with a median age of 30.
Better adherence to MD was associated with higher Bacteroides and Paraprevotella abundance, but there were no sex-based differences in alpha and beta diversity indices. Based on age, the researchers found that good compliance reduced 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 correlation with red meat intake while it was directly correlated with total sugars and NSPs.
Better adherent subjects also showed differences in pathways related to bladder cancer, polycyclic aromatic hydrocarbon degradation, and vasopressor-regulated water reabsorption. They showed more enzymes related to lipid metabolism and different biosynthesis processes.
conclusions
This study assessed the effect of MD on gut microbiota through a well-defined sex- and age-matched cohort, finding significant differences in microbial composition as well as adherence-related alpha and beta diversity. These findings were reinforced by the identification of functional pathways and specific bacterial taxa that differed based on adherence levels.
The small study sample size may limit the generalizability of these findings. Further studies using longitudinal designs and larger cohorts are needed to better understand how MD can enhance the microbiome and enhance health outcomes.
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