Submitted to: Journal of Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2007
Publication Date: 7/1/2007
Citation: Hambidge, K.M., Westcott, J.E., Lei, S., Grunwald, G., Krebs, N.F., Mazariegos, M., Solomons, N.W., Raboy, V. 2007. Intestinal excretion of endogenous zinc in guatemalan school children. Journal of Nutrition. 137:1747-1749 Interpretive Summary: Adequate zinc nutrition is important for human health. Zinc deficiency is a serious public health problem throughout the world. It is prevalent in populations that rely on cereals and legumes as staple foods since these foods contain high levels of phytic acid. Phytic acid is not efficiently digested by humans. It binds to zinc in the intestinal tract and the bound zinc is excreted, depleting the body of this important nutrient. This problem is exacerbated by the fact that during normal digestive processes, substantial amounts of zinc that is already in the body's system (endogenous zinc) is passed into the digestive tract as part of digestive enzymes, raising the levels of zinc available for binding by phytic acid. This represents a kind of "internal excretion" or "intestinal excretion", since the zinc that is passed into the digestive tract may not be reabsorbed. The level of zinc lost via intestinal excretion was measured in Guatemalans consuming either maize with normal levels of phytic acid, or a "low-phytate" maize. In the Guatemalan population studied maize represents a major staple food. No effect of the difference in gain phytic acid on endogenous zinc excretion was observed. However, this study did show that the basic level of endogenous zinc excretion, independent of dietary phytic acid level, was approximately twice that used as the standard for estimation of dietary needs. This work contributes knowledge important to enhancing the nutritional health of people throughout the world, and advances our understanding of the nutritional biology of an important mineral nutrient.
Technical Abstract: Background: The intestine is the major route of excretion of endogenous zinc and has a key role in maintaining zinc homeostasis. Phytate has been reported to increase these losses. Objective: To determine the rate of excretion of endogenous zinc in school-aged children in a poor rural community for which maize is the major food staple and to determine the effect of a low-phytate maize on this rate. Study Design: The design was a 10-week randomized trial in which 60 children and families were fed either a local maize, a low-phytate maize or its isohybrid wild-type. At the end of this trial, a stable zinc isotope tracer was administered intravenously, enrichment measured in urine and feces, total fecal zinc also measured and rate of excretion determined by an isotope dilution technique. Results: No differences in fecal excretion of endogenous zinc occurred between groups. Mean (±SD) result (n = 53) was 1.56 (0.69) mg Zn/day or 0.07 (0.03) mg Zn/kilogram body weight/ day. Conclusions: Endogenous fecal zinc excretion rate was approximately twice the figure currently used in the estimation of Dietary Reference Intakes suggesting that current guidelines may be too low for this population. Excretion rate was not related to phytate intake.