Milk produced in the mammary glands of mammals, such as cows, humans, sheep and more, contains the sugar known as lactose. Scientists describe lactose as a disaccharide, meaning it consists of two simple sugars bound together. To digest and use lactose, your body produces an enzyme known as lactase. Failing to produce enough lactase leads to a condition known as lactose intolerance, which affects 30 million to 50 million people in the United States, according to The Ohio State University Medical Center.
Milk Components
Milk provides whole food nutrition, meaning that it contains all three macronutrients including fat, protein and carbohydrates. Carbohydrates account for approximately 4.9 percent of the milk content, with the majority consisting of lactose, according to Cornell University. Lactose provides the body with energy. For the cells to receive the energy, the lactose must be absorbed by your small intestine. In those who are lactose intolerant, the small intestine cannot absorb the large lactose molecule it needs to break it down into the two simple sugar components--glucose and galactose.
Mechanism of Lactose Intolerance
Lactase is an enzyme produced by the skin cells lining the small intestine. As lactose enters the small intestine, it comes into contact with the skin cells that absorb the nutrients. Here the lactase goes to work breaking the bond between the glucose and the galactose molecule, a process known as hydrolyzing. Without lactase present, the lactose remains intact in the small intestine and keeps moving into the large intestine. Once in the large intestine, bacteria attack the lactose, trying to break it down into smaller particles. This process produces gases, which cause symptoms such as gas, bloating and abdominal pain.
Primary Lactose Intolerance
Because babies get all their nutrition from milk, their bodies produce large amounts of lactase to break down the lactose and utilize the energy. Starting at about age 2, the production of lactase begins to decrease. Over time some people just stop producing lactase, leading to primary lactose intolerance. Although some children produce low levels of lactase, they often do not experience the symptoms of lactose intolerance until adolescence or adulthood. The National Digestive Diseases Information Clearinghouse reports that genetics may play a role in primary lactose intolerance. The trends of lactose intolerance in certain ethnic groups support this claim.
Secondary Lactose Intolerance
Secondary lactose intolerance occurs when the small intestine becomes damaged due to injury or another digestive disorder. Celiac disease damages the small fingerlike projections, known as villi, in the small intestine. Crohn's disease causes chronic inflammation in the small intestine, which can damage the cells lining the intestine. These and other intestinal diseases can affect the ability of the cells to produce lactase, leading to secondary lactose intolerance. In addition, chemotherapy--the delivery of toxic drugs to kill cancer cells--can also damage the cells of the intestines and cause secondary lactose intolerance.
