Zinc absorption

Camire (2002) showed that texturization does not seem to have a great effect on mineral retention and bioavailability. Others have reported increased retention of ascorbic acid in rice- and maize-based snacks (Hazell and Johnson, 1989 Plunkett and Ainsworth, 2007), increased iron diffusibility and absorption of iron-complexed protein (Poltronieri et al, 2000 Watzke, 1998), and no difference in iron and zinc absorption in human subjects fed textured bran-flour (Fairweather-Tait et al, 1989). 

Eairweather-Tait, S. J., Porhvood, D. E., Symss, L. L., Eagles, J., and Minski, M. J. (1989). Iron and zinc absorption in human subjects from a mixed meal of extruded and nonextruded wheat bran and flour. Am. ]. Clin. Nutr. 49, 151-155. 

L. V. Kochian. Zinc absorption from hydroponic solutions by plant roots. Zinc in Soils and Plants (A. D. Robson, ed.), Kluwer Academic Publishers, Dordrecht, The Netherlands, 1993, p. 45. 

Chairidchai P., Ritchie G.S.P. Zinc absorption by a lateritic soil in the presence of organic ligands. Soil Sci Soc Am J 1990 54 1242-1248. 

In a normal human adult, about 2 g of zinc is filtered by the kidneys daily and about 0.3 to 0.6 mg is actually excreted each day (Goyer 1986). Zinc homeostasis in rats, unlike most mammals, is maintained by zinc secretion from the intestines rather than by regulation of zinc absorption (Elinder 1986). Initial uptake of zinc from the rat gastrointestinal tract involves binding to albumin and transport of the zinc-albumin complex from intestine to liver (Hoadley and Cousins 1988). 

Renal tubular absorption of zinc in mice was impaired by certain diuretics and was further influenced by dietary proteins (Goyer 1986). Zinc absorption in rats was depressed after consumption of high levels of inorganic iron absorption was normal with organoirons (Greger 1989). 

Cows fed a low (25 mg/kg ration) but adequate zinc diet had liver zinc concentrations below the expected 125 mg Zn/kg DW increasing the total zinc dietary loading to 45 or 50 mg/kg DW is recommended for counteracting reduced zinc absorption in diets with soybean products (Binnerts... 

Crustaceans can accumulate zinc from both water and food (USEPA 1987). In uncontaminated waters, the diet is probably the major source of zinc. Absorption from the stomach is efficient and occurs, in part, via the hepatopancreas. When a large pulse of zinc reaches the blood from the stomach, some is excreted, but much is resorbed and stored in the hepatopancreas in a relatively nonlabile form. Ultimately, stored zinc is also excreted, although removal via the gut is unimportant (Bryan et al. 1986). Zinc absorption occurs initially at the gill surface, followed by transport on a saturable carrier in the cell wall, and is most efficient at low dissolved ambient zinc concentrations. Urinary excretion is an important body removal pathway, especially at high dissolved ambient concentrations when it can account for 70 to 80% of total zinc excretion (Bryan et al. 1986). 

Starcher, B.C., J.G. Glauber, and J.G. Madaras. 1980. Zinc absorption and its relationship to intestinal metallothionein. Jour. Nutr. 110 1391-1397. 

In several studies (e.g., 30-36, Table I), the effects of including "processed" fiber sources (fiber isolated from natural sources) have been investigated. Results have been contradictory for example, lOgm/day cellulose decreased zinc balances in one study (3.0) but 30 to 40g/day did not affect zinc absorption in another study (36). Processed fiber may have effects which are not indicative of the effect of a similar level of endogenous fiber from foods. In summary, daily intake levels of fiber equivalent to 20 to 30g NDF/day from food sources would not be expected to have long-term deleterious effects on mineral utilization. 

Zinc absorptions 2-fold higher with low vs high phytate bread (43)... 

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. 

Zinc. Some recent studies on the effects of soy protein on zinc utilizaton are summarized in Table IV. Young and Janghorbani (4 4) and Istfan et al. (46) compared the effects of soy isolate or soy concentrate and dried skim milk as protein sources in multi-day feeding periods. Zinc absorptions, measured by fecal monitoring of the extrinsic label given, were equivalent and no deleterious effects of soy protein were observed. In a second study, Istfan et al. (47) fed egg protein diets for 10 days and then a soy concentrate diet for 82 days. Zinc absorptions were not decreased by feeding the soy concentrate diet. 

Janghorbani et al. (58) fed isonitrogenous diets to 10 subjects for 12 days. Both an intrinsic label (chicken) and extrinsic labels were used. Zinc absorptions from an all-chicken diet and from a 50% chicken-50% soy isolate diet were equivalent. Solomons et al. (59) fed 5 or 10 subjects diets in which milk, soy isolate, and beef (or mixtures of these) were protein sources for the milk and/or soy diets, absorptions were similar "fractional" absorptions from beef bologna may have been higher than from soy bologna (Table IV). 

Wood, R. J., and Hanssen, D. A. (1988). Effect of milk and lactose on zinc absorption in lactose-intolerant postmenopausal women. /. Nutr. 118, 982-986. 

HV167 Fredlund K., E. L. Bergman, L. Rossander-Hulthen, M. Isaksson, A. Almgren, and A. S. Sandberg. Hydro-thermal treatment and malting of barley improved zinc absorption but not calcium absorption in humans. Eur J Clin Nutr 2003 57(12) 1507-1513. 

Sandstrom, B., Cederblad, A. and Lonnerdal, B. 1983. Zinc absorption from human milk, cow s milk and infant formulas. Am. J. Dis. Child. 137, 726-729. 

Zinc absorption is inhibited by most food and the elevated plasma level lasts only 5 h after a dose thus it is better given five or six times a day, 1 h before or after meals. Zinc acetate may be better tolerated than the sulfate salt. Brewer prefers 25 mg elemental zinc, administered as the acetate, five or six times a day.53 Zinc is relatively non-toxic as a drug. If more than 1 g zinc is ingested in a single dose, toxic symptoms such as abdominal pain, nausea, vomiting, fever, drowsiness and lethargy may occur. A more significant toxicity problem is zinc-induced copper deficiency which can be corrected with a supplement of 0.5 mg of copper as copper sulfate per day.53... 

There are few data in the literature concerning zinc absorption from meals. However, King, et al. (18), also using stable tracers, reported 46% absorption of zinc from a formula meal by adult women who did not use oral contraceptives. Using 65Zn tracers, Sandstrom, et al. (19) reported 15.7% absorption from a meal containing white bread, milk, and cheese. 

Absorption from white bread alone averaged 38%. Zinc absorption from other meals varied from an average of 8% from wholemeal bread to 36% from chicken (19, 20). 

It appears that 67Zn is useful as tracer for determining zinc absorption, but that 70Zn is not as suitable. This is not surprising, since 67Zn determinations are more accurate and precise than 70Zn determinations (13). 

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