When you eat a food, the acid in your body dissolves the food and kills most bacteria. The stomach empties in two to six hours. So, what happen next in the small intestine? The broken down food, now in the form is a soupy liquid, moves into the next section of the gut, a c shaped tube about 25 cm or 10 inches long that forms the first part of the small intestine.
The gall bladder and pancreatic duct deposit a cocktail of digestive enzymes into this section of the small intestine. This works on the food, breaking down carbohydrates, fats and proteins. The food then moves through the rest of the small intestine, which is about 6 meter or 20 feet long. Nutrients, minerals and water are absorbed through the walls and into the blood stream in a process that takes between three and five hours.
The inner wall of the small intestine is covered with tiny structures called villi that create a huge surface area through which nutrients can be absorbed. The large intestine, or colon, is about 1.5 meter of 5 feet long. Its main function is to absorb any remaining salt and water from the digested food. It contains a myriad of bacteria that prepare waste material for elimination.
Up to 1 liter of water is absorbed in the colon so that the contents are a semi solid mass. What remains of your meal spends between 12 and 48 hours in the colon. Waste matter then passes through to the rectum, which acts as a storage container. When the rectum is full, it triggers an elimination reflex and faces leave the body through the anus.