Effect of different calcium and phosphorus content in Mexican diets on rat femur bone growth and composition

Abstract

Mexican diets are high in Phosphorus (P) with Ca/P ratios higher than recommended for optimum bone development. Beans and tortillas are the principal energy sources in the typical Mexican diet and these items are also the contributors of Calcium (Ca) and P. In the typical Mexican diet (vegetable diet of this study), beans contribute substantial quantities of Ca (129 mg/d) and P (266 mg/d) and 274 mg Ca/d and 200 mg P/d for corn tortillas. When milk is included (mixed diet), milk provides, 447 mg Ca/d and 350 mg P/d. The objective of this study was to investigate the effect of different Ca and P content typically found in Mexican diets on the growth and composition of rat femurs. Weanling rats were fed diets with different Ca and P content for 30 days, their femurs were extracted, weighed and the Ca and P content analyzed. Dietary Ca affects bone mass and Ca bone deposition (r=0.96;P<0.05) to a much greater extent than dietary P (r=0.71;P<0.05). Even though the P was higher than Ca in the diets, the femurs had equal molar ratios of Ca and P. Ca and P content in the femur of rats fed both test diets increased but to a much lesser extent than when the animals were fed control diets. The animals fed the negative control diet or a diet deficient in Ca and P, showed a significant loss of both Ca and P in the bone when compared to the initial values (P<0.05). On diets high in Ca, final size was larger and bone weights were larger. The rats fed the test diets had significantly (P<0.05) smaller femurs. The femur weight of the rats fed the vegetable diet did not differ in weight from those animals fed a diet deficient in Ca and P. Populations like Mexicans, who depend on beans and tortillas as their primary source of energy, as well as sources of Ca, in the diet, need to find ways to improve dietary Ca intake. Maintaining adequate Ca intake appears to be more important than Ca:P molar ratios.