The Science Behind Starch Blockers (White Bean Amylase Inhibitor)
A group of doctors from The Mayo Clinic conducted a significant study on purified White Kidney Bean extract carb blockers. The doctors investigated whether commercial bean-derived α-amylase inhibitor preparations (in the 1980s) failed to decrease starch digestion in humans because of insufficient anti-amylase activity, destruction by gastrointestinal secretions, or because of decreased activity in the presence of starch.
They used a simple partial purification procedure to markedly concentrate the inhibitor (sixfold to eightfold by total protein content, and 30–40-fold by dry weight). Compared with a commercial preparation and crude bean extract, this partially purified inhibitor inactivated intraduodenal, intraileal, and salivary amylase in vitro faster and more completely (p < 0.001); its specific activity was not affected by exposure to gastric juice and was only minimally reduced by duodenal juice.
Whereas the rate of amylase inhibition by inhibitor was markedly slowed in the presence of nondietary liquid starch, dietary solid starch had only a minimal effect. Consequently, the partially purified inhibitor had no effect on liquid starch digestion, but decreased in vitro digestion of dietary starch in a dose-dependent manner (p < 0.001).
Perfusion of the partially purified inhibitor (2.0, 3.5, or 5.0 mg/ml at 5 ml/min) into the duodenum of humans rapidly inhibited >94%, >99%, or >99.9% of intraluminal amylase activity. They concluded that commercial amylase inhibitors failed to decrease starch digestion in vivo mainly because they had insufficient antiamylase activity. However, a partially purified inhibitor with increased specific activity is stable in human gastrointestinal secretions, slows dietary starch digestion in vitro, rapidly inactivates amylase in the human intestinal lumen, and, at acceptable oral doses, may decrease intraluminal digestion of starch in humans. Such an inhibitor therefore deserves further study.
Source: Layer, Peter, Gerald L. Carlson, and Eugene P. Dimagno. "Partially purified white bean amylase inhibitor reduces starch digestion in vitro and inactivates intraduodenal amylase in humans." Gastroenterology 88.6 (1985): 1895-1902.