The inhibition of human pancreatic α-amylase (HPA) enzyme activity can offer facile routes to ameliorate postprandial hyperglycemia in diabetes via control of starch digestion. The present study utilizes complementary experimental (starch digestion kinetics, fluorescence quenching, Förster resonance energy transfer and X-ray diffraction) and computational (molecular docking and dynamics simulation) methods to evaluate the HPA inhibitory activity of eight water-soluble vitamins, for the first time. In particular, ascorbic acid inhibited HPA activity via non-competitive antagonism from two allosteric sites, by channeling the inhibition towards the active site cavity via the triose-phosphate isomerase (TIM) barrel. In contrast, folic acid inhibited HPA activity by binding competitively to the active site cavity and decreasing the disorder in the neighboring loops 3 and 7, which are important mobile loops in HPA for starch digestion. The infusion of such biocompatible and nutritional water-soluble vitamins alongside starch may offer new avenues for diabetes management.