Objective Effect of feeding hyperglycemic rats the decoction of discarded yellowing Wuyi rock tea leaves on serum glucose and gut microbiota of the animals was investigated for possible utilization of the byproduct.

Methods Model type 2 diabetic rats (DC) were created by streptozotocin induction to be fed with decoction of yellowing leaves rejected in the Wuyi rock tea making process. Serum glucose and insulin as well as gut microbiota in the hyperglycemic rats were determined.

Results The fasting glucose, insulin, and HOMA-IR in blood of the treatment rats were lower than those of DC. The HE-stained rat liver and pancreatic cells showed steady improvements by the treatments. And in the guts, the relative abundance of Firmicutes significantly decreased, while Bacteroidetes increased. For comparison, the microbiota in the guts of DC at genus level were upregulated on Allobaculum, Clostridium_sensu_stricto_1, and Lachnospiraceae_NK4A136, whereas downregulated on Lactobacillus and Ruminococcus. In contrast, the microbial communities were positively changed in the treatment rats.

Conclusion The discarded old rock tea leaves seemed to contain functional ingredients therapeutic for diabetes in hyperglycemic rats. By feeding the rats with decoction of the leaves, serum glucose and gut microbiota were restored to the normal levels. The hypoglycemic effect was speculated to come from microbial modulation through glucose metabolism pathways.