Quercetin is a flavonoid that has been shown to have health-promoting capacities due to its potent antioxidant activity. However, the effect of chronic intake of quercetin on the gut microbiome and diabetes-related biomarkers remains unclear. Male C57BL/6J mice were fed HF or HF supplemented with 0.05% quercetin (HFQ) for 6 weeks. Diabetes-related biomarkers in blood were determined in mice fed high-fat (HF) diets supplemented with quercetin. Mice fed the HFQ diet gained less body, liver, and adipose weight, while liver lipid and blood glucose levels were also lowered. Diabetes-related plasma biomarkers insulin, leptin, resistin, and glucagon were significantly reduced by quercetin supplementation. In feces, quercetin supplementation significantly increased the relative abundance of Akkermansia and decreased the Firmicutes/Bacteroidetes ratio. The expression of genes Srebf1, Ppara, Cyp51, Scd1, and Fasn was downregulated by quercetin supplementation. These results indicated that diabetes biomarkers are associated with early metabolic changes accompanying obesity, and quercetin may ameliorate insulin resistance.

Colored common beans are associated with health promoting and chronic disease prevention effects. Male C57BL/6J mice were fed high-fat (HF) diets supplemented with cooked black turtle beans (HFB) to prevent obesity related insulin resistance. Mice on both HF and HFB were obese compared to mice fed a low-fat (LF) diet. Plasma low density lipoprotein (LDL) and triglyceride concentrations of mice fed HFB diet were 28% and 36.6% lower than those on HF diet. Homeostatic model assessment of insulin resistance (HOMA-IR) index of mice fed HFB diet was 87% lower than that of mice fed HF diet. Diabetes related biomarkers, gastric inhibitory polypeptide (GIP), leptin, glucagon, and inflammatory cytokines interleukin 4 (IL-4) and IL-5, 10 and 12, IFN-g and TNF-α were significantly affected by HFB diet. Pparα, Cyp7a1 and Fasn were down-regulated by HFB diet while LDL-R, Srebp-2, Adipoq and Slc2a4 were up-regulated by HFB diet. The ratio of Firmicutes/Bacteroidetes (F/B) was also decreased 64.1% by HFB diet compared to HF diet. The results indicated that cooked black turtle bean consumption could ameliorate insulin resistance and lower plasma LDL in mice fed HF diet through glucose signaling pathway and JNK/c-Jun pathway. Meanwhile, cooked black turtle bean consumption restored the gut microbiome.