Lactose is a sugar found in dairy that your body breaks down with an enzyme. Here’s how that process works and what happens when it doesn’t. Lactose is a natural, complex sugar produced in all mammalian milk that’s difficult to breakdown unless you have lactase, a protein, in your small bowel. Lactose, carbohydrate containing one molecule of glucose and one of galactose linked together. Composing about 2 to 8 percent of the milk of all mammals, lactose is sometimes called milk sugar. Lactose is a disaccharide composed of galactose and glucose, which form a β-1→4 glycosidic linkage. Its systematic name is β- D -galactopyranosyl- (1→4)- D -glucose. Lactose is sometimes referred to as “milk sugar” because it is only found naturally in the milk of mammals—including cows, goats and humans. Milk from cows and goats is used to make cheese and yogurt, but not all milk products contain the same amount of lactose. Lactose is a sugar naturally found in dairy products like milk, butter, yogurt, and more. Learn which 5 foods to avoid for lactose intolerance. Lactose is the primary sugar in milk, and its main job is providing energy. When you digest it, your body splits it into two simpler sugars, glucose and galactose, which fuel your cells. Lactose intolerance is a condition that makes it hard to digest the sugar in milk and milk products, called lactose. People with lactose intolerance often have diarrhea, gas and bloating after eating or drinking foods containing lactose. Although lactose may be detected in the faeces of people with lactose intolerance, this test is not considered reliable enough to conclusively diagnose or exclude lactose intolerance. Lactose is a major disaccharide present in milk. It is composed of two simple sugars, glucose and galactose. Cow, goat, and buffalo milk contains less lactose than human milk. It has several applications in the food industry.