Objective Exploring the effects of yellow tea leaves, a by-product of Wuyi rock tea processing, on blood glucose and gut microbiota in type 2 diabetes mellitus (T2DM) rats, aiming to provide a theoretical basis for the high-value utilization of Wuyi rock tea by-products and dietary intervention for T2DM.

Methods A T2DM rat model was established by streptozotocin induction. Successfully modeled rats were randomly divided into a model group (DC), a metformin group (ME), and low-, medium-, and high-dose tea groups (LT, MT, and HT), with an additional normal control group (NC). Rats in each group were administered by gavage once daily for 8 consecutive weeks. After the intervention, fasting blood glucose and serum insulin were measured, and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. Pathological changes in the liver and pancreas were observed by hematoxylin-eosin staining, and gut microbiota composition was analyzed by 16S rRNA high-throughput sequencing.

Results Compared with the DC group, fasting blood glucose, serum insulin, and HOMA-IR levels were decreased in all tea-treated groups, and the morphology of liver and pancreatic cells showed a trend of improvement. After modeling, the relative abundance of Firmicutes was significantly decreased, while that of Bacteroidetes was significantly increased in the gut of diabetic rats. Old leaves effectively reversed these structural changes in the gut microbiota. At the genus level, the abundances of Allobaculum, Clostridium_sensu_stricto_1, and Lachnospiraceae_NK4A136 were significantly increased, while those of Lactobacillus and Ruminococcus were significantly decreased in the DC group. After intervention with old leaves, the relative abundances of the aforementioned genera were beneficially regulated.

Conclusion Old leaves of Wuyi rock tea can regulate blood glucose and improve gut microbiota structure in T2DM rats, shifting them toward the NC group. It is speculated that old leaves may exert their hypoglycemic effect by regulating glucose metabolism pathways through the gut microbiota.