Lactose is a type of carbohydrate that can be broken down for use as energy after being eaten. Carbohydrates are created through the effects of photosynthesis on the plant pigment chlorophyll. Lactose is a disaccharide, meaning that it breaks down into two simple sugars. Lactose is the type of carbohydrate found in milk and dairy products.
Components
Lactose contains two smaller molecules, galactose and glucose. Galactose and glucose are called simple sugars, or monosaccharides. Galactose and glucose, along with fructose, another simple sugar, all have the same chemical formula, C6H12O6. The atoms are arranged differently in each, however. Lactose makes up between four to six percent of cow's milk and five to eight percent of human milk, according to Elmhurst College's Virtual Chembook.
Purpose
Because carbohydrates break down into particles that can be absorbed by the body more easily than protein or fats, they serve as the primary energy source for humans, supplying four calories per gram. Most people should consume around 50 to 55 percent of their daily calories in the form of carbohydrates, the Merck Manual's Online Medical Library suggests.
Breakdown
To be absorbed through the small intestine into the bloodstream, glucose and galactose must be split apart by an enzyme known as lactase, produced on the surface of the cells that line the small intestine. Once broken down, glucose and galactose are absorbed through the small intestine into the blood. From there, the sugars are transported into cells for use as energy along with sodium.
Lactose Problems
A large percentage of adults manufacture insufficient amounts of lactase, including 80 percent of African-Americans and Native Americans and 90 to 100 percent of Asian-Americans. People who don't make enough lactase have lactose intolerance and develop intestinal symptoms when they consume dairy products. If lactose doesn't break down in the small intestine, bacteria also present in the large intestine cause it to ferment. Fermentation produces large amounts of carbon dioxide gas, which produces the symptoms of bloating, gas, abdominal discomfort, nausea and diarrhea that typically appear 30 minute to two hours after a lactose-intolerant person ingests lactose, the Virtual Chembook explains.
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