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Metabolism of ¹⁴C-Phytate in Rats: Effect of Low and High Dietary Calcium Intakes¹

Aratoonnaz Nahapetian^*,, and Vernon R. Young^,2

^* Department of Food Technology and Nutrition, Shiraz University, Iran Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, MA 02139

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.

KEY WORDS: • calcium • phytate • myo-inositol • absorption

¹ This study was supported by grants from the Fulbright-Hays Program, Shiraz University Research Council and the Massachusetts Institute of Technology.

² To whom reprint requests should be sent at M.I.T. address.

Manuscript received 7 January 1980.

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