Oral Microbiota Characteristics in Relation to Different Dietary Patterns: A Systematic Review

Background: Diet is a key modifiable factor influencing oral health and may shape the oral microbiota. While individual nutrients, especially free sugars, have been widely studied, the role of overall dietary patterns remains unclear. This systematic review aimed to evaluate the association between dietary patterns and oral microbiota in humans. Methods: PubMed/MEDLINE, Embase, and Web of Science were searched up to 18 March 2026. Studies assessing defined dietary patterns (Mediterranean, vegan, vegetarian, omnivorous) and oral microbiota using sequencing-based methods in healthy individuals were included. Due to heterogeneity in study design, dietary assessment, and microbiome analysis, a narrative synthesis was conducted. Results: Six studies (n = 448 participants) were included. Dietary patterns showed limited impact on overall microbiota structure, with no consistent changes in alpha and beta diversity. However, differences were observed at the taxonomic level. The Mediterranean diet was generally associated with a lower abundance of periodontopathogenic taxa. Plant-based and omnivorous diets showed distinct microbial profiles, particularly involving Neisseria, Haemophilus, Prevotella, and Streptococcus. Functional activity and metabolomic profiles appeared more sensitive to dietary variation than taxonomic composition alone. Conclusions: The oral microbiota appears relatively stable across dietary patterns, although diet may influence specific taxa and functional pathways relevant to oral health. The Mediterranean diet shows the most consistent association with beneficial microbial shifts. However, evidence is limited by heterogeneity and cross-sectional designs, highlighting the need for longitudinal and interventional studies.