Lactose, also known as milk sugar, is a disaccharide consisting of one glucose molecule and one galactose molecule bonded together. Lactose comprises about 5 percent of cow's milk and is present in many milk-derived products. Lactose may also be found in processed foods containing milk as an ingredient, including baked goods, waffle and pancake mixes, instant soups, processed snack foods, processed meats and salad dressings. Lactose can function in your body in either a positive or negative manner, depending on your personal physiology.
Purpose
As a carbohydrate, lactose provides energy to your body. Carbohydrates are your body's preferred fuel source. The simpler the carbohydrate, the more readily your body digests and derives energy from it. In other words, complex starch molecules, such as those found in whole grains or vegetables, undergo a more extensive digestion process than simple sugars, such as lactose. Although comprising a relatively small quantity of the volume of milk, lactose provides a ready source of energy to your diet.
Metabolism
During carbohydrate digestion, the bulk of your dietary carbs break down to glucose. Glucose molecules, once absorbed by your small intestine, then undergo metabolism to release the energy they contain. Your body can also absorb and metabolize other simple sugars, including galactose. In this process, the galactose from lactose digestion enters your cells. With the help of metabolic enzymes, the galactose molecule is converted to glucose. Thus, one molecule of dietary lactose ultimately yields two glucose molecules available for your body's energy needs.
Intolerance
Lactose intolerance results from a lack of the digestive enzyme lactase. This enzyme splits a lactose molecule into its glucose and galactose components in your small intestine. If you lack the enzyme, either partially or completely, undigested lactose travels through your digestive tract and may cause abdominal discomfort, gas and diarrhea. More serious lactose disorders involve an inability to metabolize galactose, usually due to a defect in one or more of the enzymes responsible for converting galactose to glucose within your cells. If you do not strictly control your diet for galactose, you may suffer permanent liver or eye damage.
Other Considerations
Because milk products are a rich source of protein and calcium, you may not want to eliminate them from your diet, even if you are lactose-intolerant. Lactose-reduced and lactose-free milk are commercially available and contain added lactase to digest the milk sugar before you consume the product. In addition, you may tolerate milk products, such as yogurt or hard cheeses, that have lower levels of lactase than fluid milk.
References
- The Medical Biochemistry Page; Non-Glucose Sugar Metabolism; February 2011
- Oregon State University; Milk; July 2009
- University of Illinois McKinley Health Center; Macronutrients: the Importance of Carbohydrate, Protein, and Fat; March 2008
- National Digestive Diseases ?Information Clearinghouse; Lactose Intolerance; June 2009
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