The influence of dietary protein on lipid peroxide formation in old, food restricted rats

The effect of deetary protein on in vivo lipid peroxidation in the liver and kidney of 21 months-old, SD male rats was investigated after feeding them isocaloric diets for 60 days. Rats were divided into four groups as 5% soy protein isolate (SPI), 20% SPI, 5% casein and 20% casein diet groups and they all received 15 g food/day (59 kcal/day or 25% food restriction). The liver and kidney SOD activities, as well as thiobarbituric acid-reactive substances (TBARS), were increased in low protein fed animals. Catalase activities did not have significant differences between groups, but it was 15 times higher in the liver than the kidney. Glutathione peroxidase (GPx) showed increased activities in the liver of animals fed 5% protein diet, but the same was not observed in the kidney. Total glutathione was higher in the organs of animals fed 20% protein diet rather than 5% protein diet for both organs, liver and kidney, and values of the former were much higher than those of the latter. Though enzyme activities were not altered as a function of dietary protein level of quality, there is a strong evidence that TBARS is somehow augmented by feeding a low protein diet.