Catalyzes the NAD(+)-dependent oxidation of myo-inositol (MI) to 2-keto-myo-inositol (scyllo-inosose), and thus probably functions in a myo-inositol degradation pathway together with IolM, IolN and IolO. Has no activity with scyllo-inositol and much reduced activity (78-fold lower catalytic efficiency) with 1D-chiro-inositol. myo-inositol + NAD(+) = H(+) + NADH + scyllo-inosose kcat is 2.7 sec(-1) with myo-inositol as substrate. kcat is 1 sec(-1) with 1D-chiro-inositol as substrate. Polyol metabolism; myo-inositol metabolism. Belongs to the Gfo/Idh/MocA family.