Co-digestion of rice with commercial dietary fibers: Effects on the bioaccessibility of essential and toxic elements.

Inadequate dietary fiber intake remains a global public health concern, and increasing fiber intake through staple foods has been proposed as a practical strategy. However, whether fiber incorporation interferes with mineral bioaccessibility remains unclear. In this study, the co-digestion of three commercial dietary fibers (wheat, oat, and soy) with 15 rice samples was systematically investigated using an in vitro gastrointestinal model, focusing on the bioaccessible concentrations of essential and toxic elements. The experimental design enabled simultaneous evaluation of interaction effects and net bioaccessible outcomes. The results revealed element-fiber specific interactions during co-digestion. Importantly, dietary fibers acted as significant mineral contributors, and their intrinsic mineral content primarily governed the net increases in bioaccessible essential elements. Bioaccessible concentrations during co-digestion closely matched the sum of individual digestions, indicating predominantly additive behavior. Co-digestion with wheat fiber increased the bioaccessible concentrations of both Ca and Mg to 2.7-fold compared to rice alone while maintaining Zn levels, whereas soy fiber resulted in the highest bioaccessible Ca (5.7-fold). Notably, none of the fibers increased the bioaccessible As or Cd. These findings suggest that the bioaccessible mineral in rice-fiber systems is largely determined by additive mineral contributions rather than generalized inhibitory interactions. This work highlights the importance of evaluating net bioaccessible intake in mixed-food systems and provides a scientific basis for improving mineral nutrition in rice-based diets through rational fiber selection.