The estimates of zinc physiological requirements by the International Zinc Nutrition Consultative Group (IZiNCG) in 2004 were conspicuously low in comparison with those estimated by the Institute of Medicine (IOM) in 2001. The objective of this review is to explore the reasons for this gap and to reflect on lessons learned. All estimates of inevitable losses of endogenous zinc, especially intestinal excretion of endogenous zinc, were reviewed. An error in zinc menstrual losses, as well as a minor error in the linear regression of endogenous fecal zinc (EFZ) vs. total daily zinc absorption (TAZ) by IOM, were corrected. The review revealed an error by IZiNCG in selecting two data points for the linear regression of EFZ on TAZ. A second major reason for the “gap” is attributable to weighting of the data in the regression analysis by number of subjects per study by IZiNCG. Adjusting for these factors, together with use of the same reference data for body weights, resulted in satisfactory agreement between the two estimates of physiological requirements. The lessons to be learned from this review are discussed together with suggestions for future action by IOM as well as a constructive role for IZiNCG.