Estimation of dietary calcium utilization in rats using a biomechanical functional test

Three-point bending of femora was evaluated as a biomechanical functional test of calcium utilization in male Wistar rats fed 20% casein and soy protein diets containing different levels of dietary calcium (2·0, 0·5 and 0·05% w/w), respectively. Rats were meal-fed for 10 weeks after which animals were sacrificed and both femora removed. Femur mineral composition and biomechanical parameters: bioyield, peak force, bending failure energy and a normalized force parameter, maximum bending stress were determined. Femur calcium content and ash weight were significantly (p < 0·05) decreased in animals fed low calcium diets compared to those fed medium and high calcium diets. Femur biomechanics were not related to animal growth parameters. Femur biomechanical parameters were correlated with dietary calcium intake and femur composition in both casein- and soy-fed animals. The bioyield and peak force parameters identified were significantly (p < 0·001) correlated with femur calcium content in casein- and soyfed rats. Calcium utilization was indicated by regression equations relating bone calcium content and ash weight to bioyield and peak force, respectively, for casein- and soy-fed animals. Bending failure energy could not be reliably modelled using these same variables, suggesting that it is influenced by not only bone mineralization but possibly also the collagen matrix component. These results indicate that three-point bending can be useful in assessing calcium utilization from the diet. Bone biomechanics were not influenced by casein and soy dietary protein sources.