Intestinal fermentation lessens the inhibitory effects of phytic acid on mineral utilization in rats

The specific effects of phytic acid (PA) and resistant starch (RS) on mineral bioavailability, namely, Ca, Mg, Fe, Zn and Cu, were investigated in rats adapted to semipurified diets. The diets provided either 73 g/100 g digestible wheat starch (DS) alone, or 53 g/100 g DS plus 20 g/100 g crude potato starch (RS) and either 0 or 1.1 g/100 g PA. A period of 3 wk was first planned to adapt the rats to their respective diets. Compared with rats fed the DS diets, those fed the RS diets had significant cecal hypertrophy and an accumulation of short-chain fatty acids, together with greater cecal blood flow. RS enhanced the cecal absorption of Ca and Mg (from 0.15 to 0.55 micromol/min for Ca, and from 0.10 to 0.35 micromol/min for Mg). Mineral balance was enhanced significantly by RS (Ca, +46%; Mg +50%; Fe +20%; Zn, + 33% and Cu, +61%). PA had no significant effect on Ca or Mg solubility and absorption in the cecum, and it failed to alter significantly Ca or Mg balance. The apparent absorption of Fe, Zn and Cu was significantly lower in rats fed the DS + PA diet than in rats fed the DS diet (Fe, -35%; Zn, -28%; and Cu, -31%). In rats adapted to the RS diet, the inhibitory effects of PA were practically abolished and the mineral balance was restored to the control values. We conclude that the negative effects of PA on mineral balance are relatively minor compared with the stimulatory effect of RS.