Only 30-40% of dietary zinc is available for absorption; the majority passes directly to faeces due to its close association with compounds such as fibre and phytates.
Zinc binds to a mucosal cell membrane protein receptor. By an active transport mechanism, it is taken up into the cell. Within the enterocyte, zinc can bind to the protein metallothionein. Consequently, it is unavailable for transfer to blood and instead passes into faeces with the sloughing off of the mucosal cell.
Zinc that does not bind to metallothionein is free to combine with albumin or alpha-2-macroglobulin for blood transport.
Hence, by varying the synthesis of metallothionein within enterocytes, there is a physiological means of regulating the amount of zinc liberated to the blood.
Last reviewed 01/2018