Copper phytate

Heretofore, no economical method for preparing pure phytic acid was known. The classical method was to dissolve calcium phytate in an acid such as hydrochloric acid, and then add a solution of a copper salt, such as copper sulfate to precipitate copper phytate. The latter was suspended in water and treated with hydrogen sulfide, which formed insoluble copper sulfide and released phytic acid to the solution. After removing the copper sulfide by filtration, the filtrate was concentrated to yield phytic acid as a syrup. 

Gillooly et al. (42J observed that iron absorptions were markedly decreased by the additon of sodium phytate to test meals while similarly marked decreases in zinc absorption have been observed (36,43 Table II). Contradictory results were recently reported (23.44). Addition of high levels (1.5 to 2.9g/day) of sodium phytate did not significantly affect the apparent absorption of iron, manganese, copper or zinc. 

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. 

Zinc and copper absorption were compared in young men when a-cellulose or phytate were added to purified diets (Table IV). Copper absorption was not affected by the additions (19) but zinc absorption was significantly lower when phytate was included in the diet (18). Differences in copper absorption were between subjects also noted. ... 

Table IV. Zinc and copper absorption from diets containing phytate and fiber.

Gastrointestinal absorption, and subsequent utilization and retention by the body, of essential trace elements such as zinc, copper, and selenium can also be enhanced or diminished by the presence or absence of other trace elements and chemicals in the diet (WHO, 1996). For example, cadmium and lead absorption is enhanced when dietetic intake of calcium, iron, and phosphate is low. Phytate, an organic phosphate that is abundant in diets high in unrefined grains, especially when accompanied by high dietetic calcium, helps suppress the uptake of potentially toxic elements such as lead and cadmium, but also inhibits the uptake of essential zinc (WHO, 1996). 

I he RDA for zinc is 15 mg. With mixed diets containing phytate and fiber, about 30% of dietary zinc Is absorbed. The efficiency of absorption increases with diets containing very little zinc. Dietary zinc must replace the obligatory losses, which, at the minimum, are about 0.7 mg/day. The RDA for copper has not been determined. The National Research Council recommends 1.5 to 3.0 mg per day as a safe and adequate range of dietary copper intake for adults. The usual dietary intake of copper in the United States is about 1 mg/day. This amount is sufficient to... 

Dietary fiber and phytate. Dietary fiber and phytate are known as potential inhibitors of the absorption of divalent cations however, the literature regarding the effect of dietary fiber and phytate on the bioavailability of minerals is contradictory. Data by Yannai and Sachs (1993) indicate that phytate does not affect methylmercury absorption. Yannai and Sachs (1993) compared the absorption by rats of mercury found intrinsically in experimental fish meal with and without added phytate and found no significant differences in the absorption of Hg (93 5%) between 2 experimental fish meal diets (containing 1.4 mol Hg/kg diet), with or without added sodium phytate. The authors speculated that phytate might be preferentially bound to zinc, iron, and copper, which were present at much higher concentrations in the diet. 

The ability of zinc ions to block copper absorption, possibly by formation of- intestinal metallothionein that strongly binds copper, has led to its use in pharmacological doses in the management of Wilson s disease/ Similarly molybdate ion can form insoluble copper-molybdate complexes in the intestine that limit copper absorption. The detrimental effects of organic phosphate (phytic acid) in limiting zinc absorption are aggravated by excess dietary calcium, probably by formation of a highly insoluble Ca-Zn-phytate complex. The subject of these and other interactions has been reviewed, ... 

The iron in meats is in the form of heme, which is readily absorbed. The non-heme iron in plants is not as readily absorbed, in part because plants often contain oxalates, phytates, tannins, and other phenolic compounds that chelate or form insoluble precipitates with iron, preventing its absorption. Conversely, vitamin C (ascorbic acid) increases the uptake of non-heme iron from the digestive tract. The uptake of iron is also increased in times of need by mechanisms that are not yet understood. Iron is absorbed in the ferrous (Fe ) state (Fig. 44.6), but is oxidized to the ferric state by a ferroxidase known as ceruloplasmin (a copper-containing enzyme) for transport through the body. 

Davies NT, Nightingale R. 1975. The effects of phytate on intestinal absorption and secretion of zinc, and whole body retention of Zn, copper, iron and manganese in rats. Br J Nutr 34 243- 258. 

MICROMINERALS (Trace Elements). The importance of these essential elements may often be overlooked in investigations of the causes of heart disease, because only small quantities are required and deficiencies may develop only after long periods on poor diets. However, a variety of these elements is necessary for (1) various functions of the cardiovascular system, and (2) the regulation of metabolic processes which directly or indirectly affect the heart and blood vessels. Furthermore, they are often the nutrients most likely to be removed during the processing of such foods as whole grains, or to be rendered unavailable because they are bound by naturally occurring food constituents like oxalates and phytates, or by food additives like ethylenediaminetet-raacetic acid (EDTA). (EDTA is added to foods so as to bind metals like copper and zinc which may cause discoloration of the products.) Therefore, a discussion of some trace elements and their functions follows. 

NOTE WELL The biological availability of zinc in different foods varies widely meats and seafoods are much better sources of available zinc than vegetables. Zinc availability is adversely affected by phytates (found in whole grains and beans), high calcium, oxalates (in rhubarb and spinach), high fiber, copper (from drinking water conveyed in copper piping), and EDTA (an additive used in certain canned foods). 

Most magnesium is located in the aleurone layer and is commonly bound to phytates. Therefore, most of the magnesium is lost during milling processes (Table 3.6). Cereals are also considered an important source of potassium, but they are practically devoid of sodium. Most of the iron, zinc, and copper are in the pericarp, germ, and aleurone therefore, considerable amounts are lost during milling operations. 

The issue of bioavailability from food sources and the interactions between food groups and copper availability remains a critical question. Lonnerdal et al. demonstrated that heat treatment of cows milk formula decreases the copper bioavailability. Transitional complexes form in the milk upon heating that have a similar configuration to copper and thereby directly inhibit copper absorption. High doses of zinc also reduce copper bioavailability, as does combined iron and zinc supplementation. The dilemma is how to prepare an infant formula containing adequate copper, iron, and zinc that will meet the RDA for copper. Other nutrients dramatically affect copper absorption from foods. Soy protein-based diets promote less copper retention in tissues than lactalbumin-based diets. However, it is unclear if this effect is solely due to the soy protein composition or to the higher zinc in these soy-based formulas. In animals, phytate causes a drop in serum copper but human stable isotope studies reveal no... 

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