Phytates mineral binding

Grains contain only small amounts of calcium compared to much greater quantities of phosphorus, but much of the latter element may be in the form of unavailable phytates— which bind with minerals such as calcium, iron, and zinc so as to hinder their absorption. It is noteworthy that the yeast leavening of breads breaks down some of the phytates. (Whole grains contain more phytates than milled grains.)... 

Cereals are considered a very poor source of calcium (Sema-Saldivar 1993). However, some food processes such as nixtamalization for tortilla making (Chapter 9) and cooking in the presence of ashes (i.e., alkaline to. Chapter 16) increase its concentration (Sema-Saldivar et al. 1990, 1991, 1992). Phosphorus is the mineral present in the highest amounts unfortunately, its bioavailability is questionable because most is bound to phytic add (Lasztity and Lasztity 1990). Phytates also bind other cations such as iron and zinc, considerably lowering their availability. The phytic acid... 

Zinc Deficiency. A nutritional problem associated with consumption of large amounts of whole wheat products is the unavailability of dietary zinc, first observed in a patient with immature development and dwarfism in southern Iran (17). The patient showed marked improvement when placed on a well-balanced, nutritious diet for a year. In 1962, similar patients were observed in Egyptian villages. A deficiency of zinc was identified as the primary reason for the development of this condition. This deficiency of zinc results from the binding of that metal by the phytates present in whole wheat (18). Even when an excess of zinc is present in the diet, if conditions are right, that zinc may be complexed with the phytate and thus rendered unavailable to the body (see Mineral nutrients). Thus, a zinc deficiency may develop when its dietary level appears adequate but the diet contains large amounts of a food, such as whole wheat, that is high in phytates. 

Phytates found in cereals, legumes, nuts and oil seeds form complexes with minerals, the mineral-phytate complexes in decreasing order of stability being zinc > copper > nickel > cobalt > manganese > calcium. Thus, zinc is affected most. An increase in pH results in phytic acid becoming more ionized and initiates binding to cations. 

Diets based on unleavened wheat bread contain a relatively large amount of phytic acid (inositol hexaphosphate), which can bind calcium, iron and zinc to form insoluble complexes that are not absorbed. Phytases in yeast catalyse dephosphorylation of phytate to products that do not chelate the minerals. 

Chelating agents—Other molecules that bind (chelate) mineral elements may alter the amounts of chromium which are absorbed and retained within the body. For example, oxalate (occurs in spinach and rhubarb) increases, while phytate (present in whole grains and legumes) decreases the absorption of chromium salts. However, the feeding of oxalate also causes a great increase of chromium in the urine. 

However, it is rich in phytates, phosphorus compounds that bind many of the essential minerals so that they are not readily absorbed. It is noteworthy that the leavening of breads with yeast overcomes much of the effects of phytates. ... 

Phytates—These poorly utilized compounds of phosphorus—which are present in the outer layers of grains—bind with such minerals as calcium, iron, and zinc and interfere with their absorption. Hence, mineral deficiencies may occur in people whose diets are composed mainly of whole grain breads. For example, diets based upon these breads were found to be the cause of combined zinc and protein deficiencies which led to stunting of growth and impaired sexual development of males in rural Iran. ... 

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