BACKGROUND: A number of clinical trials have successfully been performed using 
whey and/or soy proteins in the treatment of many diseases. They both have 
antioxidant properties, which appears to be a factor in aerobic physical 
performance as well. In addition, these are the most often used supplements that 
sportsmen take to increase their performance.
AIM OF THE STUDY: To investigate the effect of whey and soy protein 
supplementation on redox parameters in the muscle, on body weight, and body 
composition in swimming-trained and non-trained animals.
METHODS: The effect of whey and soy protein-isolate supplementation on muscle 
redox parameters, body weight, and body composition in trained and non-trained 
mice was investigated after a single exhaustive bout of exercise. Steady state 
free radical concentration measured using electron spin resonance (ESR) 
spectroscopy, reduced and oxidized glutathione ratio, thiobarbituric 
acid-reactive substances (TBARS), and protein carbonyl levels of the red leg 
muscle were measured.
RESULTS: Free radical concentrations and glutathione composition of the tissue 
indicated that whey protein supplementation of the regular diet was able to 
prevent oxidative stress regardless of training. Soy protein supplementation 
decreased TBARS only in the muscle of untrained animals, while training per se 
lowered protein damage in all investigated groups. A mixture of soy and whey 
protein supplementation resulted in leaner animals after training, but had no 
synergistic effect on either of the measured redox parameters.
CONCLUSIONS: Athletes consuming these supplements could train with higher 
exercise intensity. The antioxidant effect of the two proteins is based on 
different mechanisms of action.