MECHANISMS OF GASTROINTESTINAL ABSORPTION - DIETARY MINERALS AND THE INFLUENCE OF BEVERAGE INGESTION

In the absence of exogenous (dietary) factors, there are five major de terminants of mineral absorption: (a) degree of solubilisation in the stomach, (b) extent of hydrolysis/endogenous ligand interaction in the small bowel and lability of this new metal species; (c) transport thr ough the mucus layer; (d) efficiency and mode of mucosal uptake which is partly dependent on (b), although some metals may be facilitated wi th active processes; (e) transport into blood which, for some minerals , is regulated by intra-mucosal and systemic factors. Addition of exog enous factors may either alter the luminal complex presented to the mu cus/mucosa, or directly affect the permeability of the mucosa. Whether these effects increase or decrease absorption of the mineral depends on its normal mode and efficiency of uptake. Thus citrate increases th e absorption of aluminium (normally poorly absorbed) but reduces the a bsorption of calcium (normally well absorbed). Finally, assessment of such effects requires the use of a validated model and should be consi dered in the context of real dietary situations.