May 1, 1999
By: Andrea Platzman, R.D.
Lactose intolerance seems to be everywhere these days. And no, it's not some form of peculiar prejudice, but rather, the inability to digest significant amounts of lactose, the predominant sugar in milk.
During the digestive process, lactose is broken down into two simpler sugars - glucose and galactose. This requires lactase, an enzyme produced by the epithelial cells in the small intestine, as well as by activity of intestinal flora. Lactose intolerance results from a lack or deficiency of lactase - without adequate amounts of this enzyme, much of any lactose consumed passes undigested into the large intestine. There, it absorbs water and becomes fermented by bacteria in the colon, resulting in diarrhea, gas and abdominal cramps. Symptoms usually begin 30 minutes to two hours after consumption of dairy foods.
The diagnostic gold standard for determining lactose intolerance is the breath hydrogen test. For this test, a load of lactose is consumed, and the concentration of hydrogen in the breath, which normally is very small, is measured at regular intervals. Increased hydrogen levels indicate improper digestion of lactose, and reflect the presence of excess gas produced by bacteria in the lower intestine.
Lactose tolerance tests also are used to determine intolerance. For this procedure, the subject takes an oral dose of 50 grams of lactose, and blood-glucose levels are monitored. If, after 20 to 30 minutes, abdominal cramping and/or diarrhea occur, and a low, or flat, blood-glucose curve results, then lactose intolerance is confirmed. Unchanged blood-glucose levels indicate that the liver is not changing galactose into glucose, as occurs during normal digestion of lactose.
Form and manifestation
Lactose intolerance is not a disease. Rather, it is a condition stemming from a number of factors. Dietary modifications easily remedy this common condition, which can be classified as congenital, meaning that one is born lactose intolerant, or as acquired, meaning that one becomes lactose intolerant later in life. Congenital lactose intolerance is extremely rare. Acquired lactose intolerance takes on two forms, secondary and primary. Secondary acquired lactose intolerance can result from disease or certain medications, while primary acquired lactose intolerance - the most common form of the condition - is genetic.
"Lactose intolerance affects the majority of people - in fact, it may be abnormal to digest milk," states Suzanne Teuber, M.D., assistant professor of internal medicine, division of rheumatology, allergy and clinical immunology, University of California, Davis. "In persons descended from populations originally from Africa; southern or eastern Asia, including Eskimo and Native American nations; the Pacific; Australia; or the Mediterranean, the ability to digest lactose usually decreases after infancy. In the United States, about 25% of the population is lactose intolerant, compared to about 75% worldwide," she says.
Lactase, present only in small quantities, is the last intestinal enzyme to develop in children, and also the first to disappear. Generally, in populations with the highest lactose intolerance rate, those affected have lost their lactase at a younger age than affected individuals from other populations. Some will lose their tolerance after a year, others after five years. Alternately, lactase production may fall very gradually throughout life, so that symptoms from consuming dairy products will not be noticed until adulthood. However, most people can tolerate 12 grams of lactose each day - an amount approximately equivalent to that found in one glass of milk.
Lactose intolerance levels vary from person to person, depending on how much lactase the body produces. Those with mild lactose intolerance can drink several glasses of milk before experiencing any discomfort, while those with more severe cases may experience distress after merely having one slice of chocolate cake. In addition, some people may be sensitive to other sugars in addition to lactose. For example, they may not be able to tolerate raffinose, a sugar found in beets, green peas, lima beans and molasses.
Alleviate the bloat
Lactase production cannot increase once it has declined. But, there are ways to alleviate the symptoms of lactose intolerance. Prevention is key - i.e., consumption of foods naturally low in lactose. It's also important to check food labels for the following lactose-containing ingredients: whey, whey protein concentrate, caseinate, dry milk solids, milk by-products, malted milk, buttermilk, sour or sweet cream, nonfat dry milk and curds, as well as cheese.
A 1995 study by C. Saavedra, M.D. and colleagues at Johns Hopkins University, published in the American Journal of Clinical Nutrition, compared the effects on children of live-culture yogurt and pasteurized yogurt to those of regular milk. Live-culture yogurt caused significantly fewer symptoms of lactose intolerance than milk, with pasteurized yogurt somewhere in between. Lactose was apparently absorbed into the large intestine more slowly after the yogurt consumption, thus not overloading the colon and not causing as many symptoms.
If sufficiently potent, lactase drops provide benefits and can be mixed into dairy foods. Fermented dairy foods such as yogurt and kefir can also help with lactose digestion, due to their probiotics, or "friendly bacteria," that metabolize undigested carbohydrates via fermentation. (For more information on beneficial bacteria, see Food Product Design's August 1998 Nutrition Notes, entitled "Friendly Colonization.")
Since lactose-intolerant individuals avoid dairy products, they must also maintain adequate calcium intake. Calcium requirements vary with one's age and sex, according to the National Institute of Health's Consensus Development Panel on Optimal Calcium Intake. Essential to the growth and repair of bones, calcium is especially important in preventing osteoporosis, or weakening of the bones. Recent studies suggest that this mineral also helps reduce the risk of developing high blood pressure and some forms of cancer.
Andrea D. Platzman is a registered dietitian who is a consultant to the food industry, and regularly writes for nutrition publications. She earned a master's degree in nutrition from New York University and has a culinary and business background.Back to top
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