Phytate - an undesirable constituent of plant-based foods?

Phytate (myo-inositol (1, 2, 3, 4, 5, 6) hexakisphosphate), a naturally compound formed during maturation of plant seeds and grains is a common constituent of plant-derived foods. The major concern about the presence of phytate in the diet is its negative effect on mineral uptake. Minerals of concern in this regard would include Zn 2+, Fe 2+/3+, Ca 2+, Mg 2+, Mn 2+, and Cu 2+. Especially zinc and iron deficiencies were reported as a consequence of high phytate intakes. In addition, a negative effect on the nutritional value of protein by dietary phytate is discussed. Consumption of phytate, however, seems not to have only negative aspects on human health. Dietary phytate was reported to prevent kidney stone formation, protect against diabetes mellitus, caries, atherosclerosis and coronary heart disease as well as against a variety of cancers. Furthermore, individual myo-inositol phosphate esters have been proposed to be metabolically active. Dmyo-inositol (1, 2, 6) trisphosphate, for example, has been studied in respect to prevention of diabetes complications and treatment of chronic inflammations as well as cardiovascular diseases and due to its antiangiogenic and antitumour effects myo-inositol (1, 3, 4, 5, 6) pentakisphosphate was suggested as a promising compound for anticancer therapeutic strategies. Ke ywo rd s : antinutrient, cancer, caries, coronary heart disease, diabetes mellitus, mineral availability, phytate, protein digestibility, renal lithiasis ❚ The proper chemical designation for phytic acid is myoinositol (1, 2, 3, 4, 5, 6) hexakisphosphoric acid. Salts of phytic acid, designated as phytates, are found in plants, animals and soil. Phytate is ubiquitous among plant seeds and grains, comprising 0.5 to 5 percent (w/w) [ 1 ]. It is primarily present as a salt of the monoand divalent cations K+, Mg 2+, and Ca 2+ and accumulates in the seeds during the ripening period. In dormant seeds phytate represents 60 to 90 percent of the total phosphate. Only a very small part of the myo-inositol phosphates exist as myo-inositol pentaand tetrakisphosphate of unknown isomeric state. Phytate is regarded as the primary storage form of both phosphate and inositol in plant seeds and grains [ 1 ]. In addition, phytate has been suggested to serve as a store of cations, of high energy phosphoryl groups, and, by chelating free iron, as a potent natural anti-oxidant [ 2, 3 ]. Because phytate is a naturally occurring compound formed during maturation of plant seeds and grains, it is a common constituent of plant-derived foods. Depending on the amount of plant-derived foods in the diet and the grade of food processing, the daily intake of phytate can be as high as 4500 mg [ 4 ]. In average, the daily intake of phytate was estimated to be 2000–2600 mg for vegetarian diets as well as diets of inhabitants of rural areas of developing countries and 150–1400 mg for mixed diets. Phytate behaves in a broad pH-region as a highly negatively charged ion and has therefore a tremendous affinity for food components with positive charge(s), such as minerals, trace elements and proteins [ 3, 5 ]. There is a large body of evidence that minerals are less available from foods of plant origin as compared to animal-based foods. Furthermore, phytate-phosphorus is less nutritionally available, since phytate is not hydrolysable quantitatively in the human gut [ 6 ]. Furthermore, it was demonstrated that phytate-protein interactions negatively affect protein digestibility in vitro and that the extent of this effect depends on the protein source [ 5 ], but a negative effect of phytate on the nutritional value of protein was not clearly confirmed in studies with simple-stomached animals [ 7 ]. Consumption of phytate, however, seems not to have only negative aspects on human health. Dietary phytate was reported to prevent kidney stone formation [ 8 ], protect against diabetes mellitus [ 9 ], caries [ 10 ], atherosclerosis and coronary heart disease [ 11 ] as well as against a variety of cancers [ 12 ]. P h y t a t e a s a n a n t i n u t r i e n t The major concern about the presence of phytate in the diet is its negative effect on mineral uptake. Minerals of concern in this regard would include Zn 2+, Fe 2+ / 3+, Ca 2+, Mg 2+, Mn 2+, and Cu 2+ [ 13, 14 ], but also a negative effect on the nutritional value of protein by dietary phytate is discussed [ 5 ]. Phytate – an undesirable constituent of plant-based foods? Phy t ate i s k now n f o r i t s ne gat i ve e f f e c t o n miner a l upt ake b u t o n t he ot her s ide new ev idence show s t hat p hy t ate reveals s ever a l p os i t i ve e f f e c t s o n human heal t h as we l l . 3 B Y U R S U L A K O N I E T Z N Y , K L A U S D I E T E R J A N Y , R A L F G R E I N E R * W I S S E N S C H A F T L I C H E A R B E I T E N