Effects of soy protein isolate and soy peptide preload on gastric emptying rate and postprandial glycemic control in healthy humans

This study aims to compare the effects of soy protein isolate (SPI) and soy peptide (PEP) preload 30 min before a 75-g oral glucose tolerance test (OGTT) on the gastric emptying rate, plasma insulin, and blood glucose responses. Nine healthy young subjects were evaluated on four occasions. The participants consumed a 200-ml solution containing either 20 g of SPI or PEP in experiment 1. In experiment 2, 30 min after consuming either 20 g of SPI or PEP solutions, an OGTT was performed to evaluate the individual glycemic response. The gastric emptying rate was measured by the .sup.13C-sodium acetate breath test. Blood glucose and plasma insulin were measured before and after consuming either the SPI or PEP solutions and during the OGTT. In experiment 1, plasma insulin levels were higher 30 min after consuming the PEP solution than after the SPI solution. PEP resulted in a faster gastric emptying rate than SPI. In experiment 2, just before performing the OGTT, the plasma insulin response was higher for PEP than for SPI. Fifteen minutes after starting the OGTT, the blood glucose response was lower after consuming PEP than after SPI. The gastric emptying rate tended to be faster after consuming PEP than after SPI (p = 0.08). A PEP preload might be slightly more effective for the suppression of postprandial blood glucose excursion compared with SPI; thus, a PEP preload potentially induces an enhanced insulin response just before the OGTT.