Antioxidants are compounds that counteract the harmful effects of free radicals. These effects could otherwise negatively affect DNA, fat, and protein metabolism and promote disease.
Furthermore, antioxidants protect your pancreas from free-radical damage — an additional antidiabetic effect.
Banaba leaves can neutralize free radicals due to their high content of antioxidants like phenols and flavonoids, as well as quercetin and corosolic, gallic, and ellagic acids.
One 15-day study in rats found that 68 mg per pound (150 mg per kg) of body weight of banaba leaf extract neutralized free radicals and other reactive species while regulating levels of antioxidant enzymes.
Still, human studies on the antioxidant effects of banaba leaves are lacking.