The absorption and retention of P increased linearly
(P < 0.001) at a rate of 0.77 and 0.70 g/d, respectively,
per gram of daily STTD P intake (Fig. 2a and
2b, respectively). Absorption and retention of P were
highly predictable from the STTD P intake, with R2 of
0.94 and 0.93, respectively. Calcium intake, however,
showed a quadratic effect (P < 0.001) on absorption
and retention of Ca (Fig. 2c and 2d, respectively). The
predicted inflection point of the absorption and retention
curves indicated that Ca intakes of 35.50 and
32.96 g/d yielded maximum absorbed (11.98 g/d) and
retained (11.44 g/d) Ca, respectively. Absorption and
retention of Ca were highly predictable from the Ca
intake, with R2 of 0.87 and 0.90, respectively.