Soy protein and isoflavonoids in soybeans exhibit the improvement of
insulin resistance. Our previous IN VITRO study showed that
Chungkookjang (CKJ), fermented unsalted soybeans, had better
antidiabetic actions than cooked unfermented soybeans (CSB) by increasing
isoflavones aglycones and small
peptides. We investigated whether 40% fat diets with different
protein sources such as CSB, CKJ, and
casein modulated peripheral
insulin resistance in 90% pancreatectomized (Px) diabetic rats. The Px rats weighing 209+/-14 g were freely provided
casein, CSB, or CKJ diets for 8 weeks. Both CKJ and CSB increased whole body
glucose disposal rates and
glucose uptake into skeletal muscles of Px rats as much as
rosiglitazone plus
casein treated rats during euglycemic hyperinsulinemic clamp. In addition, CKJ and CSB decreased hepatic
glucose output at hyperinsulinemic clamped states, compared to the
Casein group. The reduction of hepatic
glucose output was greater in CKJ than CSB. This reduction was associated with enhanced
tyrosine phosphorylation of IRS2 and
serine (473) phosphporylation of Akt, indicating improved hepatic
insulin signaling. This improved signaling led to decreased
phosphoenolpyruvate carboxykinase expression to reduce hepatic
glucose output. In conclusion, fermented soybeans mainly with BACILLUS SUBTILIS improved hepatic
insulin sensitivity better than unfermented soybeans by enhancing hepatic
insulin signaling cascade in diabetic rats.