The role of molecular biology in understanding structure/function relationships as well as the influence of metabolic processes on host nutrition is becoming increasingly important. Not only is this field having a major effect in elucidating the detailed structure of nutritionally important enzymes but it is also allowing the nutrition scientist to study metabolic function and the significance of different pathways in whole animals. In this review, the use of gene transfer studies, in particular, the creation of transgenic animals to study mechanisms in which nutrients may regulate gene expression is discussed. Although these studies are presently quite specific, it is envisioned that these studies will ultimately lead to a better understanding of dietary host interactions, which may lead to the ability of the clinician to optimize dietary intake in order to more favorably modify metabolic disorders.