The gastrointestinal tract is a long, muscular tube responsible for the digestion of food, assimilation of nutrients and elimination of waste. This is achieved by secretion of digestive enzymes and absorption from the intestinal lumen, with different regions playing specific roles in the processing of specific nutrients. These regions come into play sequentially as ingested material is moved along the length of the GI tract by contractions of the muscle layers. In some regions like the oesophagus transit it rapid and measured in seconds while in others like the colon transit is measured in...