Decreased plasma levels of cholecystokinin in healthy males after chronic ingestion of a heat-treated soya product

Administration of raw soya containing a trypsin inhibitor stimulated excessive release of cholecystokinin (CCK) which led to pancreatic hypertrophy, hyperplasia and cancer in the rats (Booth et al. (1964) Proc. Soc. Exp. Biol. Med., 116, 1067). More postprandial CCK release in healthy humans was observed after ingestion of a single dose of raw soya than heat-treated soya (Calam et al. (1989) Br. J. Nutr., 58, 175). The effect of chronic ingestion of a heat-treated soya product on postprandial CCK release was investigated in six healthy adult males after ingestion of a 36-oz. portion of soymilk daily for 1 month and at 2-3 months after termination of soymilk ingestion. Subjects fasted for 15 h, ingested Lipomul (1.5 g/kg) and provided blood at timed intervals for CCK analysis. The results show that 1-month ingestion of soymilk decreased the magnitude of Lipomul-induced postprandial CCK release in plasma of all six subjects by 5-60% (P < 0.05) compared to those obtained at 2-3 months after the withdrawal from soymilk ingestion. Plasma pancreatic polypeptide (PP) levels were similarly decreased in five of the six subjects by 19-67% (P = 0.03) in line with the regulation of PP by CCK. Thus, prolonged exposure of humans to a heat-treated soya inhibited slightly meal-induced CCK release in contrast to that found in rats after raw soya diets.