CALCIUM-ABSORPTION AND BONE UTILIZATION IN SPONTANEOUSLY HYPERTENSIVERATS FED ON NATIVE AND HEAT-DAMAGED CASEIN AND SOYBEAN PROTEIN

The effects of dietary protein on Ca bioavailability and utilization i n bone were examined in male spontaneously hypertensive rats (SHR) fed on diets containing either casein (200 g/kg (control), 60 g/kg or hea t-damaged (HD) 200 g/kg) or soya-bean protein isolate (200 g/kg (contr ol), 60 g/kg, or HD 200 g/kg). Casein was heat-damaged to limit casein ophosphopeptide (CPP) production in order to evaluate casein enhanceme nt of Ca bioavailability. All diets contained an adequate level of Ca (5 g/kg). A 24 h mineral balance study was performed when animals were 10 weeks old, followed by measurement of in situ paracellular Ca disa ppearance, femur mineralization and biomechanics at 14 weeks of age. D igestibility of soya-bean and both HD proteins estimated in vitro was reduced compared with native casein. Animals fed on HD and 60 g/kg pro tein diets exhibited decreased (P < 0.05) body weight gain, dry matter intake and feed efficiency compared with controls. The ileal disappea rance of Ca-45 was lower (P < 0.05) in animals fed on HD casein and al l the soya-bean protein diets. Ca balance was not strongly affected by dietary treatments. A significant (P < 0.05) interaction between prot ein source and reduced protein intake was observed for femur calcifica tion and physical measurements. Femur bending failure energy and biome chanical force measurements were reduced (P < 0.05) in HD and 60 g/kg casein and soya-bean protein fed animals. These findings suggest that whole-body Ca homeostatic mechanisms were involved in compensating for reduced Ca bioavailability and retention from casein diets modified t o reduce protein digestibility and CPP production.