Metabolism defines life. Metabolism generates energy for the cell, but it also makes building blocks for proteins and DNA. Importantly, metabolism also produces signaling molecules that regulate physiology across organs in addition to cellular mechanisms. What are the blind spots of metabolomics data today? How can we use metabolomics data to understand metabolic networks in cells, organs, and body fluids? How much can biochemical pathways be trusted in guiding our understanding, and how much do we need to extend our scope of metabolism to integrate transporters, feedback regulation, and novel epimetabolites? In this short course, we will review major concepts in metabolism and regulation of enzymes, give practical examples of how to carefully interpret metabolomic results, and set a foundation of chemical reactions that govern metabolism in the cell.