Multiple: Lactose Intolerance
Multiple: Lactose Intolerance
Lactose intolerance occurs when a person cannot digest lactose, a sugar found in milk and other dairy products. Lactose intolerance develops when lactase, an enzyme that is needed to break down milk sugar into simpler sugars, is less available or absent.
Lactose intolerance is a very common chronic digestive disorder in which a person's intestinal tract lacks the ability to make lactase, an enzyme that breaks down lactose, or milk sugar, into two simpler sugars that the body can use. A person can have a lactase deficiency without having the symptoms of lactose intolerance.
Lactose intolerance is not the same as being allergic to cow's milk. An allergy to cow's milk concerns a person's immune system, whereas lactose intolerance has to do with the process of digestion.
Lactose intolerance may be caused by any of three different factors. One is normal aging. As people get older, their small intestine produces lower amounts of lactase. After the lactase production drops below a certain point, the person may experience the symptoms of lactose intolerance.
A second cause of lactose intolerance is diseases of the intestines or surgical procedures in which part of the small intestine is removed. These
disorders or operations may affect the part of the small intestine that secretes lactase. The third cause of lactose intolerance is genetic. A few people inherit lactose intolerance from both parents and are affected from birth.
The symptoms of lactose intolerance usually begin within half an hour to two hours after drinking milk or eating a meal high in dairy products. The person typically experiences diarrhea, which is the most common symptom of lactose intolerance, along with a gassy, bloated feeling, abdominal cramps, and possibly nausea. The severity of the symptoms is not necessarily related to the amount of milk or dairy products that were consumed but rather to the person'sage, ethnicity, and the speed of his or her digestive processes.
In most cases, lactose intolerance is part of the normal human developmental process. Most mammals stop producing lactase after they are weaned because they are eating solid food instead of drinking milk from the mother. Humans begin to slow down the production of lactase some time around age three to five years; thus most human adults are at some risk of developing lactose intolerance.
Foods to Watch
Foods that are naturally high in lactose (in addition to milk) include butter and sometimes margarine; buttermilk; cottage cheese, cream cheese, and ricotta cheese; half and half, light cream, and whipping cream; ice milk, sherbet, ice cream, evaporated milk, and dry powdered milk; milk chocolate; whey; and yogurt.
Foods that contain hidden lactose include hot dogs, cold cuts, bologna, sausages, pancakes, creamy salad dressings, creamed soups, breaded meats, commercial pie crust and pie fillings, caramels, fudge and other chocolate candies, prepared cakes and sweet rolls, powdered coffee creamers, imitation dairy products, party dips, cream-based cordials, certain breads, sauces and gravies, frosting, certain prepared or processed foods, some prescription medications, and some over-the-counter medications.
It is noteworthy, however, that the levels of lactose intolerance vary quite widely among different ethnic groups. In some groups, almost 100 percent of the adult population may be lactose intolerant. In the United States and Canada, lactose intolerance is estimated to affect between 20 and 60 percent of the adult population. In terms of specific ethnic groups, people of Dutch, Swedish, German, or other northern European descent have low rates of lactose intolerance (about 5 percent); persons of southern European ancestry have rates between 18 and 25 percent; African Americans have a rate around 45 percent; persons from Japan or southeastern Asia have rates above 95 percent; and Native Americans are almost 100 percent lactose intolerant.
One theory that has been proposed to explain these differences is the long-standing differences among human societies in milk consumption after childhood. In Asia and Africa, children were rarely given milk after being weaned; in these societies, lactase production generally falls by 90 percent by the time the child is four years old. In societies in which milk consumption continues into adult life, however, a mutation on chromosome 2 that bypasses the normal shutdown of lactase production became widespread in the population. Thus members of these groups can continue to consume milk and dairy products throughout their adult lives. Some researchers have traced the mutation back as far as 4500 BCE in both Sweden and the Middle East.
Lactose intolerance results from a drop in or disruption of the production of lactase in the small intestine. Lactase is produced by specialized cells in the membrane that lines the villi, which are small finger-like projections on the walls of the small intestine. The production of the enzyme may drop at a certain age or because a disease or radiation treatment for cancer has damaged the villi of the small intestine.
The symptoms of lactose intolerance are diarrhea, bloating, nausea, and a gassy feeling within thirty minutes to two hours following a meal high in dairy products. They do not include fever, bleeding from the digestive tract, or weight loss in adults. People who have these symptoms should be checked by their doctors for other disorders of the intestines.
Diagnosis of lactose intolerance is based on a patient's history, particularly a detailed history of the patient's consumption of dairy products. Many people underestimate the amount of milk or products containing lactose that they consume; they may not think of yogurt or ice cream, for example, as milk products. After getting a complete picture of the patient's diet, the doctor will usually suggest cutting out dairy products for a week or so in order to see whether the symptoms improve. If they do, further testing may be unnecessary.
There are three tests that can be used, one of which is generally given only to infants and small children. It is a test that measures the acidity of the child's stool sample. Undigested lactose ferments inside the intestine and forms an acid that can be measured in the stool sample.
The most common diagnostic test used in adults is the hydrogen breath test. The patient is asked to drink a liquid containing a high level of lactose. The doctor then measures the amount of hydrogen in the breath at certain intervals. Undigested lactose reaches the colon and ferments, causing hydrogen and other gases to be released, absorbed by the intestines, and eventually exhaled. Large amounts of exhaled hydrogen indicate that the patient's body is not digesting lactose completely and that the patient is probably lactose intolerant.
The third type of diagnostic test involves taking a small sample of tissue from the lining of the small intestine and measuring the amount of lactase present in the tissue sample. This type of test requires a specialized laboratory to evaluate the results, however, and is rarely used outside clinical research.
There are several treatment options for lactose intolerance:
- Completely eliminating milk and dairy products from the diet. This change in diet usually requires careful reading of labels on other foods because many processed foods contain milk or milk solids (see sidebar). In addition, some drug manufacturers use lactose as a binding substance to carry the active ingredient in the medication. The patient may need to check with the doctor or pharmacist about any prescription medications they may be using to see if the drugs were formulated with lactose.
- Eliminating dairy products from the diet for a time and then gradually reintroducing small amounts of them. Some people can tolerate small amounts of yogurt or milk after avoiding them completely for a few weeks.
- Using specially manufactured lactose-free milk products or soy products and other plant-based substitutes for milk.
- Taking dietary supplements that contain lactase. Products like Lactaid, Dairy Ease, and Lactogest can be purchased without a prescription.
People who are concerned about the risk of osteoporosis (brittle bones) can take calcium supplements to keep their bones strong rather than getting their calcium from milk. Patients should ask their doctors how much calcium they should be getting from other sources. Most adults should not take more than 1,200–1,500 milligrams of calcium per day.
Most people recover completely by removing milk products from the diet or by substituting reduced-lactose or lactose-free dairy products for those that contain lactose.
There is no way to prevent congenital or adult-onset lactose intolerance.
Lactose intolerance is not a life-threatening condition. Most people can manage quite well by using milk substitutes, watching the amount of milk and other dairy products that they consume, or by taking over-the-counter lactase supplements. There are also a number of cookbooks with lactose-free recipes or recipes that use milk substitutes.
SEE ALSO Celiac disease; Crohn disease; Irritable bowel syndrome; Osteoporosis
WORDS TO KNOW
Chronic: Recurrent or long-term
Congenital: Present from birth.
Lactase: An enzyme that breaks down lactose into simpler sugars during the process of digestion.
Lactose: A complex sugar found in milk and other dairy products. It is sometimes called milk sugar.
Villi (singular, villus): Small finger-like projections along the walls of the small intestine that increase the surface area of the intestinal wall.
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