Soy protein isolate in the presence of cornstarch reduces body fat gain inrats

The objective of the present study was to determine the combined effects of dietary protein and carbohydrate sources on total body energy and protein and fat gains as well as on plasma insulin and glucose and tissue lipoprote in lipase activity in male Sprague-Dawley rats fed semipurified diets for 2 8 days. The diets varied in both protein and carbohydrate sources, namely, casein-cornstarch, casein-sucrose, soy protein isolate (SPI)-cornstarch, SP I-sucrose, cod protein - cornstarch, and cod protein - sucrose. When SPI wa s combined with cornstarch, lower total body energy and fat gains were obse rved compared with the combination of either casein and sucrose, casein and cornstarch, or SPI and sucrose. Plasma glucose and insulin concentrations in addition to total and metabolizable energy intake and body weight gain w ere lower in rats fed the SPI-cornstarch diet than in those fed the casein- sucrose diet. Feeding the SPI-cornstarch diet compared with feeding either the casein-cornstarch or the SPI-sucrose diet also caused lower plasma gluc ose concentrations and a concomitant trend (p = 0.06) to reduced energy int ake and body weight gain. Therefore, the reducing effects of the SPI-cornst arch diet compared with the casein-cornstarch, the casein-sucrose, and the SPI-sucrose diets on body energy and fat gains may result from reductions i n energy intake and in plasma glucose concentrations.