Digestion is the process by which ingested materials are reduced to molecules of small enough size or other appropriate characteristics for absorption, i.e., passage through the gut wall into the blood stream. This generally means that proteins are hydrolyzed to amino acids or to polypeptide chains of a few amino acids, digestible carbohydrates to simple sugars, and lipids to fatty acids and glycerol. Materials not absorbed are by definition indigestible and are eventually voided as faeces. Digestibility ranges from 100 percent for glucose to as little as 5 percent for raw starch or 5-15 percent for plant material containing mostly cellulose (plant fibre). Digestibility of most natural proteins and lipids ranges from 80 to 90 percent.