Ongoing efforts to develop microbiota-directed foods (MDF) provide potentially new ways for improving health status. A MDF could alter the structural and functional configuration of a consumer’s gut microbial community, provide substrates for microbial transformation to biomolecules necessary for a healthy state, or act through a combination of these mechanisms. The development of MDFs promises to expand our view of ‘essential nutrients’ and prompt questions about how they should be classified and regulated.