Accuracy of methods estimating calcium and phosphorus intake in daily diets.

Three different methods of estimating calcium and phosphorus content were compared with the chemical analysis of 20 daily diets taken from general hospital and cafeteria menus, individual food records, and menus designed for research. Comparisons of chemical analyses with estimated values showed an insignificant trend toward underestimation of calcium content; all methods significantly underestimated phosphorus content. On the average, estimates of phosphorus content deviated from actual by approximately 250 mg/day. Diets with a greater proportion of processed, convenience, or restaurant foods deviated by more than 350 mg/day. Our findings suggest that estimates of calcium intake calculated from available food composition tables are within an acceptable range of error; however, phosphorus intake is significantly underestimated by 15% to 25% of the actual level. For accurate calculation of phosphorus content, nutrient composition sources must be updated to reflect present industrial use of phosphate-containing additives.