The only food source to naturally contain lactose is milk produced by mammals. If you suffer from a digestive disorder associated with lactose, known as lactose intolerance, read food labels because manufacturers add lactose to a variety of other foods, such as baked goods, processed breakfast cereals, breakfast drinks, lunch meats, salad dressing and many snack foods. Understanding lactose can help the 30 million to 50 million people in the United States that suffer from lactose intolerance, according to the Ohio State University Medical Center.
Structure
Lactose consists of carbon, hydrogen and oxygen molecules, which classifies it as a carbohydrate molecule, or sugar molecule. Lactose is classified as a disaccharide sugar molecule because it consists of two simple sugars -- glucose and galactose -- bound together. The lactose in milk exists in two separate forms, known as alpha-lactose and beta-lactose, which differ in the orientation of one of the carbon and hydrogen atoms.
Properties
As a sugar, lactose tastes sweet. When compared to sucrose, which reaches 100 percent on the sweetness scale, lactose is not as sweet. The relative sweetness of lactose lies at 20 percent. Lactose is a stable component of milk and does not react with other chemicals. Dehydrating milk by removing all of the water concentrates the lactose and turns it into a powder. This explains why non-fat dry milk powder contains 62g of lactose per 1 cup of powder and fluid milk contains 11g of lactose per 1-cup serving, according to the University of Virginia Health System.
Digestion
As a carbohydrate, lactose provides the body with energy. The body breaks down carbohydrates and converts them into glucose -- the type of sugar the cells use. Because the lactose molecule consists of both glucose and galactose, it is too large to absorb through the lining of the small intestine. The skin cells of the small intestine produce the enzyme known as lactase, which breaks the bonds between the glucose and galactose molecules.
Lactose Intolerance
Babies exclusively drink milk, making lactase the first and only carbohydrate consumed by babies. To promote digestion, a newborn baby produces large amounts of lactase. Beginning around the age of 2, the production of lactase begins to decrease. By adulthood many people fail to produce enough lactase to effectively digest the lactose in milk, resulting in lactose intolerance. When the body cannot break down and absorb lactose, the lactose travels into the large intestine, where bacteria break down the lactose and cause the production of gas. Lactose intolerance causes symptoms of bloating, abdominal pain and diarrhea. These symptoms typically begin 30 minutes to two hours after the consumption of milk or other products containing lactose, according to the National Digestive Diseases Information Clearinghouse.
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