Carbohydrate

Carbohydrates are a broad class of organic compounds that include sugars, starches, and fibers. They consist of carbon, hydrogen, and oxygen, typically with a hydrogen–oxygen ratio of about 2:1, and are often represented by the formula (CH2O)n. Common monosaccharides include glucose, fructose, and galactose; disaccharides such as sucrose, lactose, and maltose; and polysaccharides such as starch, glycogen, cellulose, and chitin.

Monosaccharides are the simplest units and can be joined to form disaccharides, oligosaccharides, and polysaccharides through glycosidic bonds. They are classified as aldoses or ketoses based on the functional group, and the type of glycosidic linkage (for example, alpha or beta) influences properties and digestibility. Starch and glycogen consist of α-linked glucose units and serve as energy storage in plants and animals, respectively, while cellulose consists of β-linked glucose units and provides structural support in plants. Chitin is a structural polysaccharide containing N-acetylglucosamine.

Biological roles include providing a rapid energy source through glycolysis, storing glucose as glycogen in animals and starch in plants, and forming structural components in nature. Dietary fiber, comprising various non-digestible carbohydrates, is important for gut health and is fermentable by intestinal microbiota, producing short-chain fatty acids.

Dietary and metabolic context: digestion begins with salivary amylase and continues with pancreatic amylase in the small intestine, where monosaccharides are absorbed into the bloodstream. Carbohydrate intake influences blood glucose regulation and can participate in protein and lipid glycosylation and cell signaling. Sources include cereals, fruits, vegetables, and legumes, with guidelines often recommending emphasis on whole grains and fiber while limiting added sugars and refined carbohydrates.