Relationship between green tea intake and human gut microbiota on glucose metabolism: a four-season nutritional survey

Background and objectives: Little is known about the extent to which depends on the association between green tea intake and human gut microbiota (HGM) on glucose metabolism. This study aims to examine the biological process related to glucose metabolism by modifying the human gut microbiota HGM via green tea intake, considering seasonal variations. Methods: At each season, 89 non-diabetic participants supplied blood and faecal samples, 3-day weighed dietary records. The relative abundance of HGM was profiled using a next-generation sequencing approach. Biomarkers of glucose metabolism such as fasting blood glucose, haemoglobin A1c and insulin were measured. The respective associations among green tea and catechins intake, the HGM and the biomarkers of glucose metabolism were analysed using linear mixed-effect model with multiple imputation for missing values. We used a false discovery rate p-value to adjust for multiple comparisons with a threshold of < 0.20. Mediation analysis was performed to determine whether the HGM can explain the effect of green tea intake on glucose metabolism. Results: Green tea intake was negatively associated with fasting blood glucose and insulin (p < 0.05), marginally lower in autumn than in winter. Green tea intake was not related to any HGM, while the relative abundance of Actinobacteria and Bifidobacterium were associated with lower insulin and HOMA-IR (false discovery rate p < 0.20). The mediation effect of HGM was not found. Conclusions: In non-diabetic participants, we demonstrated that habitual consumption of green tea, and two types of bacteria separately modulate insulin secretion to improve glucose metabolism, which was influenced by the season.