Impact of diet and nutritional status on gingival crevicular fluid metabolome and microbiome in people with type 1 diabetes: a cross-sectional study.

People with type 1 diabetes (PwT1D) are at higher risk of developing periodontal diseases. We investigated the impact of dietary habits on the gingival crevicular fluid (GCF) microbiome and metabolome in PwT1D. The oral and periodontal examination was performed and GCF sampled. Genomic DNA was extracted, bacterial 16S rRNA sequenced and concentrations of short-chain fatty acids and trimethylamine derivatives determined. Pro-healthy (pHDI) and non-healthy diet indices (nHDI) were calculated using the validated Questionnaire of Eating Behaviours. In total, 110 participants were included (mean age 27.1 ± 6.0 years, 60.0% male). In 65 PwT1D, the mean duration of diabetes was 15.5 ± 8.4 years and mean Hba1c% 6.97 ± 0.95% (53 ± 2.2 mmol/mmol). 22 cases of mild gingivitis (G) were identified, all in the T1D group. There were no significant differences in the frequencies of pHDI categories between study groups (T1D with G, low 19 [86.4%] and moderate 3 [13.6%]; T1D without G, low 28 [66.7%] and moderate 14 [45.2%]; control, low 30 [68.2%], moderate 14 [31.8%]; p = 0.213). GCF microbiome composition did not differ between pHDI categories. In PwT1D and G caproic acid was higher in low vs. moderate pHDI category (3.5 [0.9-4.9] vs. 0.64 [0.49-NA] umol/l, p = 0.04). In people with T1D without G, isocaproic acid and glycerophosphorylcholine were lower in low vs. moderate pHDI category (0.14 [0.13-0.46] vs. 0.45 [0.18-1.24] umol/l, p = 0.032, and 71.23 [32.83-120.40] vs. 129.8 [70.5-228.1] ng/ml, p = 0.013). This was the first study to report on the impact of diet on GCF in PwT1D. The state of periodontal tissues was worse in people with T1D, overweight and with a worse quality diet. Alterations in the concentrations of selected GCF metabolites suggest an indirect association between the quality of diet and contents of pro-healthy and non-healthy products on the state of periodontium.