APPLICATION OF COMPARTMENTAL MODELING TO DETERMINATION OF TRACE-ELEMENT REQUIREMENTS IN HUMANS

The potential of compartmental modeling for determining dietary requir ements of the trace elements is explored. Transport kinetics of tracee and tracer within a physiologically meaningful arrangement of compart ments were simulated by using whole body copper (Cu) metabolism in adu lt humans as an example. The simulation was based on known, quantitati ve Cu metabolism, and required a non-steady-state model rather than a more conventional steady-state model. The simulation indicated that a reduction in dietary Cu intake could result in (1) loss of Cu from sto rage compartments, (2) maintenance of homeostasis by adaptive changes in dietary Cu absorption and endogenous excretion, or (3) a response i ntermediate between the two. By performing tracer experiments, it shou ld be possible to determine the relative significance of mechanisms 1 and 2 in response to progressively smaller dietary intakes of Cu. Whet her the body conserves Cu by adapting metabolically to low Cu intake o r, alternatively, undergoes significant Cu loss because of an inabilit y to adapt, may be an important factor in recommending a dietary requi rement. The basic structure of the whole-body model of Cu metabolism u sed in this study has features consistent with the metabolism of other trace elements. Thus, the present example may also provide an approac h to the study of dietary requirements of other elements.