Sweet Saliva Trial: Exploratory Evaluation of Salivary Microbiome Responses to Three Thai Desserts

Several studies on diet and microbiome have predominantly focused on the gut microbiome. However, much of the salivary microbiome remains unexplored. This study examined the influence of Thai desserts with varying glycemic indices on the salivary microbiome. A total of 30 healthy adults aged 18–45 years were enrolled in a randomized trial and allocated to one of three intervention groups, with each receiving a culturally specific Thai dessert standardardized to provide 50 g of available carbohydrates: Phetchaburi’s Custard Cake (PCC; low-GI, 192 g), Saraburi’s Curry Puff (SCP; medium-GI, 98 g), or Lampang’s Crispy Rice Cracker (LCRC; high-GI, 68 g). Salivary and dessert microbiome compositions were characterized at baseline and 24 h post-intervention using 16S rRNA sequencing to evaluate bacterial diversity and relative abundance across multiple taxonomic levels. Firmicutes were highly abundant (over 76%) in all Thai desserts tested. Proteobacteria were found in both SCP (15.1 ± 6.6%) and LCRC (6.5 ± 3.4%). Actinobacteriota was slightly higher in the high-GI group (6.3 ± 3.1%) compared to the medium-GI group (3.0 ± 2.2%). Bacillus was dominant in PCC, while Streptococcus, Carnobacterium, and Clostridium sensu stricto 1 were prevalent in SCP. Anoxybacillus, Clostridium sensu stricto 12, Terrilactibacillus, Geobacillus, and Weissella were found in LCRC. Desserts with different types of glycemic index showed modest short-term changes in the relative abundance of some salivary bacteria. Notably, Porphyromonas showed a relative increase in the high-GI group compared to the low-GI group (1.8 [0.3, 4.0] vs. −1.9 [−3.2, 0.8], p < 0.05), while Streptococcus, saccharolytic bacteria, slightly increased in both the high-GI and medium-GI groups. Prevotella showed a slight relative decrease in the low-GI group. Although these microorganisms have been previously associated with dysbiosis and periodontitis in longer-term studies, the clinical relevance of these short-term compositional changes remains unclear and should be interpreted with caution. These preliminary findings suggest that local Thai desserts with varying GIs may be associated with transient shifts in salivary microbiota composition; however, whether such changes contribute to dysbiosis or adverse oral health outcomes requires further investigation through longitudinal studies with larger sample sizes.