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TABLE 14-3 Qualitative Bioavailability of Zinc According to Diet Characteristicsa

Bioavailability

Dietary Characteristics

High

Refined diets low in cereal fiber and phytic acid, with adequate protein primarily from meats and fish

Phytate/zinc molar ratio < 5

Medium

Mixed diets containing animal or fish protein

Vegetarian diets not based primarily on unrefined, unfermented cereal grains

Phytate/zinc molar ratio 5–15

Low

Diets high in unrefined, unfermented, and ungerminated cereal grains, especially when animal protein intake is negligible

High-phytate soy protein products are the primary protein source

Diets in which ≥ 50 percent of energy is provided by high phytate foods (high extraction rate [90 percent] flours and grains, legumes)

Phytate/zinc molar ratio > 15

High intake of inorganic calcium (> 1 g/day) potentiates the inhibitory effects of these diets, especially when animal protein intake is low

a The phytate content of foods is provided by Hallberg and Hulthen (2000). The zinc content of foods is available from the U.S. Department of Agriculture at http://www.nal.usda.gov/fnic/foodcomp.

SOURCE: Modified from WHO (1996).

tiles for intake were less than 40 mg/day for all adults in both the NHANES III and CSFII surveys), when intake from supplements is added, higher proportions are above the UL. This is not unexpected, as many multiple vitamin-mineral supplements contain 15 mg of zinc. On the other hand, zinc intakes below the EAR are also fairly common. The dilemma, then, is how to ensure adequate zinc nutriture in the population while avoiding intakes in excess of the UL. Even in populations with low mean zinc intakes, care must be taken not to intervene in ways that would move a substantial proportion of the population above the UL. For example, widespread fortification of the food supply with zinc may not be appropriate, even if the prevalence of inadequacy in a population is high. More targeted approaches, such as increased consumption of zinc-rich foods by those at a high risk of inadequacy, should be considered.



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