Patterns of Elemental Excretion in Long Term Balance Studies

Duplicate self chosen complete daily diets (including water and beverages) and total daily urinary and fecal excreta of two men for a period of 50 weeks have been analyzed for 22 elements. Although the actual items of food and drink chosen by these individuals differed considerably and the variation in elemental intake and excretion was quite wide, when considered over this long period, the patterns of excretion were remarkably similar. For those elements excreted almost entirely in urine, the ratio of the amount excreted in urine to the total amount ingested agrees very well with the ICRP-59 values for f1, the fraction absorbed from the gut of the amount ingested. For other elements the ratio is not a valid estimate of f1 since reexcretion of the absorbed element into the gut is not taken into account. Estimation of the amounts of strontium and calcium which are absorbed and reexcreted into the gut within a period of 24 days after ingestion have been made from a study of the correlation between the fecal output of these elements and the intake by ingestion in the previous 24 days. The value for f1 for strontium, including reexcretion into the gut, has been estimated as 0.34 which agrees very well with the accepted value of 0.3. The value estimated for calcium is below the accepted value, indicating that there are components of endogenous excretion which continue to occur after 24 days.