Siamak T. Nabili, MD, MPH
Siamak T. Nabili, MD, MPH
Dr. Nabili received his undergraduate degree from the University of California, San Diego (UCSD), majoring in chemistry and biochemistry. He then completed his graduate degree at the University of California, Los Angeles (UCLA). His graduate training included a specialized fellowship in public health where his research focused on environmental health and health-care delivery and management.
Bhupinder Anand, MD
Lactose Intolerance Overview
Lactose intolerance is a common disorder caused by the inability to digest lactose, a carbohydrate found in milk and milk products. It typically causes symptoms of bloating, flatulence, diarrhea, and abdominal pain. Avoidance of milk and other dairy products alleviates most symptoms of lactose intolerance.
Lactose molecules cannot be directly absorbed by the body. Therefore, lactose has to be split into smaller molecules in order to be absorbed and transported across the wall of the intestines. Normally, lactose is broken up by an enzyme (protein that expedites chemical reactions in the body) called lactase. This enzyme is located on the lining of the intestines (the brush border) and helps to break up lactose into its smaller carbohydrate components, glucose and galactose. These two smaller molecules are more easily absorbed by the body and used for metabolism.
Lactose intolerance is caused by a deficiency of lactase in the intestinal wall. As a result, the entire lactose molecule travels undigested in the small and large intestines. The lactose molecules draw water into the intestines (by a process similar to osmosis). This results in faster transit through the intestines, thus making the process of digestion even more difficult. Eventually, bacteria present in the large intestine (colon) begin to digest (ferment) the lactose molecule by utilizing their own lactase enzyme, producing hydrogen gas and smaller molecules as byproducts. The combination of these processes leads to the symptoms of lactose intolerance: bloating, flatulence, diarrhea, and abdominal pain.
Lactase enzymes levels are highest after birth and gradually decline thereafter. In African Americans, Asian Americans, and Native Americans the overall incidence of lactose intolerance may be greater than 75% of the adult population. In Northern Europeans and Caucasians, the incidence rate is much less, typically under 25% of the adult population. In Hispanics, 50% of the adult population may have lactose intolerance, whereas, the highest rates are seen in some Asian populations, with prevalence rate greater than 90%.
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