Antiminerals are substances that interfere with absorption or metabolic utilization of minerals. Some examples are phytic acid, oxalic acid, glucosinolates, dietary fiber, and gossypol.
Phytic acid’s negative effect on iron absorption has been known for decades. Phytic acid is found in bran and germ of many plant seeds and in grains, legumes, nuts and species. In addition, phytic acid can compromise the absorption of magnesium, zinc, copper, and manganese, usually forming precipitates. Formation of protein–phytate complexes during processing has been associated with a reduction in bioavailability of minerals such as Ca, Zn, Fe and Mg. On the other hand, fermentation and other processing techniques are useful in reducing phytate levels.
Oxalic acid, like phytic acid, reduces the availability of bivalent cations. Sources of oxalate include spinach, beets, potatoes, tea, coffee, and cocoa. Tea drinking was associated with concerns for Ca deficits via complexes, which apparently can be counterbalanced by using milk with tea drinking.
Dietary fiber, can affect calcium, magnesium, zinc and phosphorus absorption. Collectively, dietary fiber refers to food components in plants cell walls that are not digested. Dietary fiber can act like ion exchangers and bind minerals.