Drugs and other xenobiotics (foreign compounds) are consumed with food, presenting the potential for interactions that may modify the biological activity of both nutrients and xenobiotics. The complexities associated with the biological fate of both classes of compounds yield a multitude of potential interactions, making the prediction of specific interactions a complicated task. However, the similarities between the biological processes involved in the biological fate of both xenobiotics and nutrients allow a logical approach to the understanding and prediction of interactions. For example, for either a xenobiotic or nutrient to produce a systemic effect, it must be absorbed. There are similarities between the factors that influence the availability and absorption of both xenobiotics and nutrients. It is at these points of similarity that interactions are most likely to occur. This is also true for the other major processes involved with the biological fate of both xenobiotics and nutrients, such as distribution, metabolism, and excretion. An understanding of these processes and the most likely points of interaction is the first step in understanding and acquiring predictive ability of the potential interactions between nutrients and drugs, as well as other xenobiotics.