Paracellular calcium absorption, femur mineralization and biomechanics in rats fed selected dietary proteins

<p>The absorption of 45Ca from the distal section of the lower small intestine, and its subsequent deposition in the femur were examined in male Wistar rats fed diets containing 20% casein (C), whey protein (W), a milk protein concentrate (MPC), and a soy protein isolate (SPI), respectively. These experiments were performed along with in-vitro studies designed to estimate the relative digestibilities of the dietary protein sources. In the animal experiments, all diets contained an adequate calcium level (0.7%). Individual rats were meal-fed for 10 weeks, after which calcium absorption was measured from the disappearance of 45Ca from the ligated ileal loop; as well, femoral deposition of 45Ca and mineral composition were examined. Estimates of calcium utilization were made from femur and tibia biomechanical measurements. A markedly lower digestibility of the soy and whey proteins was observed compared to the casein and milk protein concentrate sources, respectively. There were no differences in the daily body weight gain, and plasma calcium levels. The absorption of 45Ca from the ileum was significantly (p = 0.043) lower in SPI-fed rats, compared to C-, W- and MPC-fed animals. There was no treatment effect on femoral 45Ca deposition, total Ca, Mg or Ca/PO4 ratio. A significant correlation between femur calcium content and bone strength was determined; however, there was no treatment effect on either femur or tibia biomechanical properties. These results indicate a similar utilization of calcium in animals fed dietary proteins that may differ in digestibility.</p>