In the mid-1980s, a Mexican/US consortium conducted an intensive, longitudinal study of the functional consequences of mild-to-moderate malnutrition in six villages in the Solis Valley, 160 km NW of Mexico City. The modal diet is found to be low in diversity; 50-70% of dietary energy is obtained from maize (corn) and maize contains phytate and Ca, potent inhibitors of Zn and Fe absorption. Zn deficiency is endemic and appears to retard infants’ growth and development. As part of a larger project on the processes by which elements flow from rocks and waters to crops and to teeth (see Levigne et al, this meeting), here we focus on the significance of diet and well waters for enamel zinc concentrations. Dyads of pregnant women and their newborns were studied from ~ 3 months IU to 6 postnatal months. Prenatally and postnatally calcified enamel of exfoliated deciduous teeth was analyzed via Laser-Ablation-ICP-MS (n=45). Because Zn is a highly regulated essential metal, we predicted that both dietary Zn dietary intake and Zn concentration of community well waters might not affect Zn absorption. In fact, there was no association between water and dietary Zn and tooth Zn content. Whereas the phytate and Ca content of diets is known to decrease Zn absorption, we predicted and found that tooth Zn concentrations are negatively correlated with total dietary phytate (r=-.404) and Ca (r=-.476). The relationship between Zn content of enamel and physical growth is complicated by the source of calcium: either energy dense maize or micronutrient dense dairy products. For Zn, we suggest that you are not what you drink or eat, but what you absorb. Supported by NIH CRUI project # DBI 78793.