Human metabolism: metabolic pathways and clinical aspects

All mammalian energy is derived from food, in three chemical forms: carbohydrate, lipid, and protein, each providing a unique advantage in energy provision. Metabolism describes the series of chemical reactions that are concerned with the provision of energy to biological systems. They may be divided into reactions involved in energy mobilization/yield (catabolism: demand exceeds supply), and energy storage (anabolism: supply exceeds demand). Regulation of these pathways is critical for homeostasis, and derangements in metabolism are seen in a wide variety of pathological processes. Many common diseases have a metabolic aetiology, whilst others affect patient metabolism with significant clinical consequences. Understanding metabolism is key to the treatment of many common diseases, notably diabetes, as well as providing a rational basis for managing critically ill patients with sepsis and trauma, and underpinning clinical nutritional support.