Carbohydrates are a large group of compounds whose primary function is as an energy source. They are composed of carbon, hydrogen and oxygen. The ratio of hydrogen to oxygen is usually 2:1.
The simplest forms are the monosaccharide sugars of which glucose holds prime importance. Two monosaccharides may join to form a disaccharide; the polymeric combination of many monosaccharides gives rise to the polysaccharides. Glycogen is an important energy storage compound in animals. Cellulose is a component of dietary fibre. Both are polysaccharides.
Glycoproteins, the combination of protein and carbohydrate, are vital for immune and plasma membrane functions. Tissue plasminogen activator is a glycoprotein.
A typical developed world adult diet contains approximately 250-500 g/day of carbohydrate constituting:
- 180-300 g/day of starch, glycogen or cellulose
- 80-150 g/day of sucrose
- 20-50 g/day of lactose
- 10-30 g/day of fructose and glucose
Pathology may affect any stage of carbohydrate metabolism from digestion e.g. lactose intolerance, to storage e.g. glycogen storage diseases.