Inhibitory effects of isolated inositol phosphates on zinc absorption in humans

Inositol hexa phosphate (phytic acid) forms poorly soluble complexes with zinc, resulting in reduced absorption. During food preparation and processing phytate is partly hydrolyzed to lower inositol phosphates which have other binding properties. Zinc absorption in humans was measured in 18 women (22-37 a) by use of extrinsic labelling of meals with 65Zn and measurement of whole body retention. Inositol phosphates--400 mumol of the hexa phosphate form (IP-6), 200 and 400 mumol of the penta phosphate form (IP-5) and 400 mumol of the tetra phosphate form (IP-4)--were added to white bread and served with 200 mL of milk. The zinc content of the meal was 22 mumol. The absorption of zinc (65Zn) from white bread with no detectable phytate content was 43.3 +/- 17.9% (mean +/- SD) and from the breads with added 400 mumol of IP-6: 14.3 +/- 3.2%; 200 mumol of IP-5: 27.1 +/- 5.3%; 400 mumol of IP-5: 18.1 +/- 4.2%; and 400 mumol of IP-4: 41.5 +/- 11.3%. The results indicate that IP-6 and IP-5 have zinc-absorption depressing properties, while IP-4 added in isolated form is relatively inert as regards zinc absorption. However, a comparison with earlier obtained results from zinc absorption studies indicate that results obtained with isolated inositol phosphates can not directly be extrapolated to the phytate contents of foods.