This study tested the use of an amylase inhibitor preparation on starch digestion and post prandial hormone responses in humans. Four subjects were fasted and then intubated with an oroileal tube to obtain samples from the duodenum, jejunum, and terminal ileum. After intubation, subjects ingested 50 g of rice starch given with placebo; on the second day, starch was given with the amylase inhibitor. Results showed that the amylase inhibitor significantly reduced amylase activity in all areas of the GI tract by more than 95% for 1 to 2 hours. This reduced dietary starch digestion and uptake in the small intestine, markedly reduced postprandial release of insulin and gastric inhibitory polypeptide, and altered postprandial upper gastrointestinal motor function. It also reduced the early postprandial plasma glucose rise by 85% and eliminated the late postprandial glucose fall to below fasting levels as well as ceasing postprandial plasma concentrations of insulin, C-peptide, and gastric inhibitory polypeptide.