Humans along with most all living things evolved in an environment that included daily oral exposure to naturally occurring microparticles and nanoparticles to include dietary and non-dietary substances. The highly absorptive gastrointestinal tract (GIT) of the human and other animal species is very well suited for the absorption of small particles with dimensions of less than 1 µm. The primary function of the GIT is generally recognized as the processing of food materials and absorption of essential nutrients to provide the materials required for cellular growth and metabolism and maintaining the homeostasis of normal systemic functions. The physical characteristics that should be addressed for nanomaterials that may enter the GI tract as well as other routes of exposure include: size and size distribution, composition, structure and morphology, surface chemistry, macromolecular weight, surface area, porosity, solubility, surface charge density, purity, sterility, and stability. In general, nanoparticle absorption of food materials can be divided into three major phases: luminal, mucosal, and postabsorptive.