Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of carbohydrates in living organisms.

The most important carbohydrate is glucose, a simple sugar (monosaccharide) that is metabolized by nearly all known organisms. Glucose and other carbohydrates are part of a wide variety of metabolic pathways across species: plants synthesize carbohydrates from atmospheric gases by photosynthesis, which can then be consumed by other organisms and used as fuel for cellular respiration. Oxidation of one gram of carbohydrate yields approximately 4 kcal of energy. Energy obtained from carbohydrate metabolism is usually stored in the form of ATP. Organisms capable of aerobic respiration metabolize glucose and oxygen to release energy with carbon dioxide and water as byproducts.

All carbohydrates share a general formula of approximately C n H 2n O n ; glucose is C 6 H 12 O 6 . Monosaccharides may be chemically bonded together to form disaccharides such as sucrose and longer polysaccharides such as starch and cellulose.

Carbohydrates are a superior short-term energy reserve for organisms, because they are much simpler to metabolize than fats or proteins. In animals, all dietary carbohydrates are delivered to cells in the form of glucose. Carbohydrates are typically stored as long polymers of glucose molecules with Glycosidic bonds for structural support (e.g. chitin, cellulose) or energy storage (e.g. glycogen, starch). However, the strong affinity of carbohydrates for water makes storage of large quantities of carbohydrates inefficient due to the large molecular weight of the solvated water-carbohydrate complex. In some organisms, excess carbohydrates are catabolised to form Acetyl-CoA, where they enter the fatty acid synthesis pathway. Fatty acids, triglycerides, and other lipids are commonly used for long-term energy storage. The hydrophobic character of lipids makes them a much more compact form of energy storage than hydrophilic carbohydrates.