Combined effects of various types of dietary fiber and protein on in vitro calcium availability

The effect of the nature of dietary fiber was determined by measuring soluble and ionic calcium using an in. vitro method. Results show the existence of a chemical interaction between calcium and fiber and/or protein. Lignin, oat bran, and wheat bran, which contain endogenous protein and phytic acid, with or without added protein, reduced calcium availability by 2-20% possibly through the formation of stable and insoluble complexes between fiber/phytic acid and calcium. When combined with fiber (with the exception of pectin), beef and casein had no significant effect on soluble calcium. When compared with the fiber-free control, soy and lignin decreased soluble calcium. As well, soy, wheat bran, lignin, and cellulose decreased ionic calcium, suggesting an interaction effect.