Metabolism is the set of chemical reactions involved in maintaining the living state of cells and the organism. These chemical reactions are organized into metabolic pathways and can be divided into two categories: catabolism, the breakdown of organic molecules such as carbohydrates, lipids and proteins with the release of energy, and anabolism, the synthesis of complex molecules such as proteins and nucleic acids from simpler compounds that generally requires energy. Metabolic pathways are evolutionarily highly conserved between species. Disorders of these processes may result from nutritional deficiencies, disease in metabolic organs such as the liver and pancreas, or genetic mutations. The human and economic impact of conditions such as diabetes mellitus, hyperlipidemia, and osteoporosis is staggering, so additional research is essential for developing preventative approaches in conjunction with therapeutic agents that can minimize the long-term effects of these progressive maladies.