Phytic Acid
Grains require careful preparation because they contain a number of antinutrients that can cause serious health problems. Phytic acid, for example, is an organic acid in which phosphorus is bound. It is mostly found in the bran or outer hull of seeds. Untreated phytic acid can combine with calcium, magnesium, copper, iron and especially zinc in the intestinal tract and block their absorption.
-Weston A. Price Foundation