Mulberry leaf extract intake reduces hyperglycaemia in streptozotocin (STZ)-induced diabetic rats fed high-fat diet

•Mulberry leaves contain 1-deoxynojirimycin, flavonoids, and phenolic acids.•Mulberry leaf extracts decreased blood glucose and increased plasma insulin in diabetic rats.•Mulberry leaf extracts exert antidiabetic and antioxidative effects in diabetic rats fed high fat diet.•Mulberry leaf extract anti-diabetic effects depend on extraction method. This study evaluated the antioxidant activity and anti-diabetic effect of mulberry (Morus alba L. wielkolistna zolwinska) leaf extracts in diabetic rats fed a high-fat diet. After initial 4-week high-fat diet, streptozotocin was injected in Wistar rats to induce non-obese type 2 diabetes. After confirmation of diabetes, animals were treated with mulberry dried leaves, leaf-derived ethanol or acetone extracts added to high-fat diet for 4 weeks. Mulberry ethanol extract with higher level of phenolics – chlorogenic acid and flavonol glucosides was more effective than acetone extract or dry leaves in the lowering of blood glucose, increasing insulin level and markers of antioxidant activity. The results confirm key mechanisms related to the effect of mulberry and its bioactive components on modulation of glucose metabolism through correcting hyperglycaemia, increasing insulin secretion, and improving antioxidant status in STZ-induced non-obese diabetic rat model. Antidiabetic effects exerted by mulberry leaves might depend on the extraction process.