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Studies on the Bioavailability of Zinc in Man. Effects of the Guatemalan Rural Diet and of the Iron-Fortifying Agent, NaFeEDTA^1,2,3,4,5,

Division of Human Nutrition and Biology, Institute of Nutrition of Central America and Panama, Guatemala City, Guatemala, Apartado 11-88, and the United States Department of Agriculture, Science and Education Administration, Human Nutrition Laboratory, Grand Forks, North Dakota 58201

By serial determination of the change in plasma zinc concentration following a standard dose of 110 mg of zinc sulfate heptahydrate, containing 25 mg of elemental zinc, the biological availability of zinc was evaluated in human subjects. Plasma zinc concentration was stable in the fasting state. Following the standard dose of zinc (25 mg) in water, plasma zinc concentration rose above the fasting, baseline levels by 61.0, 68.0, 52.0 and 37.8 µg/dl, respectively, at the first four hourly sampling intervals. Four hours after a standard meal, based on the traditional rural diet of Guatemala and consisting of 120 g of corn tortillas, 120 g of black bean gruel, 40 g of sweet rolls and 250 ml of coffee sweetened with 15 g of sugar, plasma zinc concentration was significantly lower (-18 µg/dl) than the fasting level. Addition of 25 mg of zinc to the black bean gruel in the meal prevented this decline, but did not increase plasma zinc above fasting levels; apparently zinc absorption was inhibited by the meal. Probably, phytates, dietary fiber and calcium are major factors, and coffee is a minor factor in this inhibition. The chelate of iron with ethylenediaminetetraacetate (NaFeEDTA), an iron-fortifying agent proposed for use in Guatemala, at doses of 15 mg, equivalent to that in a cup of coffee sweetened with 15 g of fortified sugar, and at doses of 40 mg, equivalent to that consumed in a day by rural Guatemalans, did not significantly depress zinc uptake. Moreover, no influence of 15 mg of NaFeEDTA beyond that of coffee or food, itself, was detected. High doses of NaFeEDTA, outside of the normal range, impaired zinc absorption, and the EDTA moiety, rather than iron, was responsible. Our data suggest that fortification of sugar with NaFeEDTA at one part per thousand would not influence zinc nutriture, but that the basic Guatemalan diet, itself, impairs zinc nutriture.

KEY WORDS: • zinc • bioavailability • high fiber diet • ethylenediaminetetraacetate • iron fortification

¹ This work was supported in part by a contract AID/TA-C-1341 from the Agency for International Development.

² Presented in part at the XI International Congress on Nutritions, Rio de Janeiro, Brazil, August, 1978, Abstracts p. 71, and at the Annual Meeting of the American Society for Clinical Nutrition, Washington, D.C., May, 1979, Am. J. Clin. Nutr. 32, 000, 1979.

³ INCAP Publication I-1024.

⁴ Address reprint requests to N. W. Solomons, INCAP, Carretera Roosevelt, Zona 11, Guatemala, Central America, 11–88.

⁵ Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture, and does not imply. its approval to the exclusion of other products that may be suitable.

Manuscript received 29 December 1978.

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