Studies on the Effect of Soy Protein Isolate Diets in Pregnant Rats and Improvement of its Nutritional Effect

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Fetal death in the last few days of pregnancy or neonatal death were observed in tats fed diets of less than 35% Soy Protein Isolate (SPI) throughout pregnancy. Among the groups of rats fed 20% SPI, 30% SPI, 35% SPI, 40% SPI, 20% SPI+0.6% L-methionine (Met). 30% SPI+0.9% Met, 35% SPI+1.1% Met, and 40% SPI+1.2% Met, the last one showed decreased neonatal death and improved biological value.Fetal growth and placental function were studied in rats on 19th and 20th day of pregnancy. Rats were fed a 10% purified whole egg protein (PEP) diet for control and a 20% SPI diet and a 20% SPI+0.6% Met diet. The food intake and body weight of the 20%SPI diet group decreased after 18th day of pregnancy.Free amino acid concentration in serum and amniotic fluid of SPI diet groups showed higher value than those of PEP diet group. This suggested that abilities of active transport of free amino acids in the placentas of SPI diet groups were inferior to that of PEP diet group. Free fatty acid concentration in serum of SPI diet groups were lower and glucose concentration in serum of SPI diet groups were higher than those values in serum of PEP diet group. Estrogen in urine of SPI diet groups were higher than that of PEP diet group in 19th day of pregnancy.These results showed that SPI intake induced changes of endocrine system in pregnant rats.