Lactose (Milk Sugar): Like sucrose, lactose is a disacharride and is commonly found in cow's milk and other dairy products. Lactose is composed of a molecule of 'galactose' that is chemically bonded to a molecule of glucose. Like sucrose, lactose cannot be absorbed by the human gut until it is broken down into individual molecules of galactose and glucose and galactose by a gut enzyme called 'lactase'. Many adult humans produce very little lactase and therefore cannot digest lactose but instead, pass the whole lactose molecule into the colon where normal bacteria feed upon it and generate a large amount of gas leading to a syndrome called "lactose intolerance".