Phytates zinc deficiency

Human food, both plant and animal, usually contains satisfactory amounts of zinc to cover the requirement for this metal, which is present within the range of few to several pg per g of product. Zinc deficiencies are usually caused by a reduction of its absorption in the gastrointestinal tract rather than by its lack. Reduction in absorption may be caused by antagonistic activity of cadmium, calcium or phytates. A decrease in assimilation of zinc is also observed among alcoholics. 

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. 

Excess calcium not only decreases the utilization of phosphorus but also increases the requirement for zinc in the presence of phytate and may result in zinc deficiency. Excess calcium also increases the requirement for vitamin K. 

The relative vulnerability of the secreted zinc to phytate complexatlon has only recently been demonstrated. The injection p zinc deficient rats intraperitoneally with a tracer dose of zlnc allows a portion of this zinc to be in equilibrium with the endogenous metabolic pool. This zinc then is secreted thru the saliva, pancreatic fluid, and bile. Those animals maintained on the phytate containing soy protein contained 2-4 times the radioactivity of the animals fed a casein protein diet (Table II). Therefore, not only does phytate affect the bioavailability of dietary zinc but also the reabsorption of endogenous zinc and thus has a net effect on zinc homeostasis. Since this total phytate effect cannot be measured ly labeling only the dietary pool, the expression of the net effect as the phytateizinc molar ratio is the most sensitive and accurate method of estimating the relative risk of zinc deficiency in any individual or population. 

The report of a WHO Expert Committee (1) emphasized the need for information on the bioavailability of zinc, since the recommended intake was dependent on this important factor. Although zinc deficiency in humans was initially reported from Iran and Egypt, adverse effects of marginal or low intakes of zinc by infants and children have subsequently been reported from other parts of the world (2). Apparently the zinc intakes in Iran and Egypt were adequate but the bioavailability was adversely affected by the high level of phytate and fibre in the diet (2). The zinc content of the modern diet is decreased by the use of refined... 

Almost all the evidence showing that phytate decreases zinc absorption in man and animals is based on pure phytate added to the diet. The effect of natural phytate is variable (18). It has, however, been reported that phytate in bran affected zinc bioavailability in the same way as sodium phytate (19). Dietary fibre in the rural Iranian diet was considered to be the main cause of zinc deficiency in Iran (20). However, the addition of 26 g of fibre from various sources to the American diet did not have any significant effect on the zinc requirements of male adults (21). Similarly, Indian men consuming a diet containing only 10.8 mg of zinc were reported to be in balance in spite of a dietary fibre intake of 50 g per day (22). Moreover, the presence of fibre and phytate in soy flour did not affect the bioavailability of zinc added as zinc carbonate, to the diet of rats (17), although others (23) have reported that the bioavailability of zinc in breakfast cereals depends mainly on their phytate-zinc molar ratio. Our results indicate that there is some, as yet, undetermined difference in the phytate or the fibre of cereals which affects the bioavailability of zinc. It may be some component of dietary fibre (24) or the intrinsic differences in the protein-phytate-mineral complex (10). 

Evidence that dietary fiber interfered with absorption of bivalent metals by the intestine was first ob -tained in connection with studies of human zinc deficiency in Iran. Human subjects who consumed purified phytate exhibited smaller feeal losses of zinc and calcium than they did when they ate equivalent amounts of phytate in the form of unleavened wheaten whole meal flat breads that are the staple food in rural Iran... 

Windisch W and Kiechgessnee M (1999a) Tissue zinc distribution and exchange in adult rats at zinc deficiency induced by dietary phytate additions ... 

Zinc deficiency occurs in populations whose diets contain high concentration of phytate, a powerful chelator, and low protein (Tapiero and Tew, 2003). Zinc deficiency negatively affects the epidermal, central nervous, immune, gastrointestinal, skeletal, and reproductive systems (Salgueiro et al, 2000,2002 Tapiero and Tew, 2003 Verstraeten ef aZ., 2004). 

In hypogonadal dwarfism, reported by Prasad et al. [47], adolescents in Iran and Egypt became zinc-deficient in consequence of high phytate content in the diet making zinc unavailable for absorption. This disease results in dwarfism, retarded sexual maturation, iron deficiency anemia, and hepatosplenomegaly. 

Zinc deficiency in humans may have different origins (see also Sec. 3.1) e.g., by diminution of intake (phytates, fibers), increased needs (pregnancy, lactation, growth), or increased losses (bums, chelating agents). 

Zinc deficiency is thought to be common in human populations living on restricted diets and to be one of the factors responsible for their poor general health. If the Zn intake is low, whether or not it is adequate will depend on other components of the diet. The endemic Zn deficiency encountered in Iran may be connected with the high phytate content of the rural diet which interferes with Zn absorption. 

Zinc is the prosthetic group for many enzymes. It is also incorporated into the receptor proteins for steroid and thyroid hormones, calcitriol and vitamin A. Recommended daily intake of zinc is 10 mg/day. Zinc is found in all tissues of the body, but it is particularly high in the bone, liver and kidney. Zinc deficiency causes growth retardation, decreased wound healing and hypogonadism (i.e. much delayed puberty). It is only normally seen in populations whose diet is based on unleavened wholemeal bread, because wheat flour does not provide much zinc, and that which is available is bound to phytate. Phytate also inhibits the absorption of iron. Zinc depletion may also be caused by drugs such as thiazide and loop diuretics, and alcohol. Zinc deficiency can be successfully treated with replacement zinc therapy. 

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