EFFECT OF DIETARY CALCIUM ON METABOLIC BALANCE OF NORMAL INFANTS

Metabolic balance studies were performed with 6 normal infants fed in a balanced cross-over design 3 formulas differing only in Ca concentration: 389, 659, and 1024 mg/l. Absorption of P was significantly affected by increasing Ca intake decreasing from 68 to 63 to 52% of intake. However, since urinary excretion of P also decreased, there was no significant effect on retention of P. Absorption of fat was slightly (but significantly) depressed by Ca, decreasing from 97.5 to 95.5 to 92.1% as Ca intake increased. The level of dietary Ca had no significant effect on absorption or retention of nitrogen, Mg, Cu, and Zn. One of the subjects had consistently lower absorption of Ca and fat than the other subjects, suggesting an absorptive defect. The decrease in fractional absorption of Ca (57 to 47 to 39% of intake) with increasing intake of Ca is compatible with adaptive regulation. On the other hand, the observation that absorbed Ca (mg/kg/day) was linearly related to intake of Ca with a slope of 0.373 suggests an alternative explanation: constant passive, concentration-dependent (slope), and constant active (y-intercept) transport of Ca over the range of Ca intakes. Thus, the findings are explainable in more than one way and do not necessarily demonstrate regulatory changes.