Protein deficiency and excess lipid synergistically augmented lipid peroxidation in growing rats

The influence of dietary protein and lipid on superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione (GSH) and tissue lipid peroxidation, as measured by thiobarbituric acid-reactive substances (TBARS), was investigated in post-weaning male Wistar rats, fed either a diet containing 5% or 20% corn oil with 5%, 10% or 20% soy protein isolate (SPI) for four weeks. TBARS concentrations in 5% corn oil group was highest in 5% SPI group for all organs, followed by 10 and 20% SPI groups in the liver and 10 and 20% SPI groups in other organs. High lipid diet significantly increased TBARS formation in the liver of 10% SPI group. The liver and kidney SOD and GPx activities were higher in 5% and 10% SPI groups than in 20% SPI group, suggesting an augmented formation of radical substrates for these enzymes in low protein groups. Organ GSH concentrations did not show a linear correlation with dietary protein level. These results suggest that protein deficiency along with high lipid intake accelerates the peroxidative damage of the tissues by increasing oxy-radical formations and/or decreasing the defense mechanism.