Metabolism of 14C-phytate in rats: effect of low and high dietary calcium intakes.
The purpose of this study was to explore in rats the in vivo metabolism of phytate, using [U-14C]phytate and to assess the effects of calcium intake on phytate and myo-inositol metabolism. Labeled phytate was prepared from wheat following injection of the plants at the milk stage with [U-14C]myo-inositol. Groups of 30-day-old male rats were adapted for at least 6 weeks either to a low-calcium (2.9 mM/100 g dry diet) or a high-calcium (30.6 mM/100 g dry diet) cereal-based diet. They were then transferred to metabolic cages, continued on their respective diets and given an oral dose of [14C]phytate or [14C]myo-inositol. Appearance of radioactivity in expired air, feces and urine was monitored for 48 hours; the rats were then killed for determination of 14C-activity in liver, kidneys, blood and femur. The high-calcium diet significantly increased the output of radioactivity in feces (54% of dose) and reduced the appearance of radioactivity in expired air (25% dose) and in body tissues following 14C-phytate administration. The high-calcium intake did not affect the fate of [14C]myo-inositol (96% of dose). These results suggest that phytate or a derivative(s) is almost quantitatively absorbed (94% of dose) when calcium intake is low (Ca/P molar ratio; 0.21) and it is extensively oxidized to CO2 (60% of dose). Thus, a high-calcium intake (Ca/P molar ratio; 2.24) inhibits the utilization of [14C]phytate. Hence, it is suggested that the impact of dietary phytate on trace mineral bioavailability will depend upon the presence of factors, including excess calcium, that alter the absorption and utilization of phytate.
D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000032:analysis; D002250:Carbon Radioisotopes; D007294:Inositol / Q000378:metabolism; D008297:Male; D009929:Organ Size; D010833:Phytic Acid / Q000097:blood / Q000378:metabolism*; D051381:Rats
D002250:Carbon Radioisotopes; D002245:Carbon Dioxide; D007294:Inositol; D010833:Phytic Acid; D002118:Calcium