The most widely used method for estimating dietary zinc requirements is the factorial approach, in which it is assumed, in adults, that the physiological zinc requirement is the lowest intake that replaces endogenous zinc losses. Presented here are the results of two reviews: a narrative review of zinc losses from the human body and a systematic review of factors affecting zinc bioavailability in adult and elderly populations. The narrative review presents data on losses from integumental and excretory routes, obtained from 29 papers published up to April 2013. The systematic review includes a total of 87 publications describing dietary factors that impact zinc bioavailability, 30 of which examined phytate. A meta-analysis revealed an overall lowering of fractional zinc absorption by 0.14 (45% of control values) when the phytate : zinc molar ratio of the test meal or diet was greater than15. These reviews provide a comprehensive resource for use in the setting of human dietary zinc requirements and emphasize the need for more high-quality data to improve estimates of zinc losses and gains.