LACTOSE INTOLERANCE
Lactose intolerance is an inability to digest and absorb lactose (the sugar in milk) that results in gastrointestinal symptoms when milk or products containing milk are drunk or eaten.
1. CAUSES OF LACTOSE INTOLERANCE
2. SYMPTOMS OF LACTOSE INTOLERANCE
3. DIAGNOSIS OF LACTOSE INTOLERANCE
4. TREATMENT OF LACTOSE INTOLERANCE
1. CAUSES OF LACTOSE INTOLERANCE
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Lactose is a larger sugar that is made up of two smaller sugars, glucose and galactose. The enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of the cells that line the small intestine.
Lactose intolerance is caused by reduced or absent activity of lactase that prevents the splitting of lactose (lactase deficiency). Lactase deficiency may occur for one of three reasons, congenital, secondary or developmental.
Lactase deficiency may occur because of a congenital absence (absence from birth) of lactase due to a mutation in the gene that is responsible for producing lactase.
This type of deficiency is due to diseases that destroy the lining of the small intestine along with the lactase. An example of such a disease is celiac sprue.
The most common cause of lactase deficiency is a decrease in the amount of lactase that occurs after childhood and persists into adulthood, referred to as adult-type hypolactasia. It is important to emphasize that lactase deficiency is not the same as lactose intolerance. Persons with milder deficiencies of lactase often have no symptoms after the ingestion of milk. A diagnosis of lactase deficiency is made when the amount of lactase in the intestine is reduced, but a diagnosis of lactose intolerance is made only when the reduced amount of lactase causes symptoms.
2. SYMPTOMS OF LACTOSE INTOLERANCE
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The common symptoms of lactose intolerance are gastrointestinal, primarily,
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Abdominal bloating
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Abdominal distension and nausea.
Symptoms occur because the unabsorbed lactose passes through the small intestine into the colon. In the colon, one type of normal bacterium contains lactase and is able to split the lactose and use the resulting glucose and galactose for its own purposes. Unfortunately, when they split the lactose into glucose and galactose, these bacteria also release hydrogen gas. Some of the gas is absorbed from the colon and into the body and is then expelled by the lungs in the breath. Most of the hydrogen, however, is used up in the colon by other types of bacteria. A small proportion of the hydrogen gas is expelled and is responsible for the increased flatus (passing gas). The un split lactose in the colon draws water into the colon (by osmosis). This leads to loose, diarrhoeal stools.
3. DIAGNOSIS OF LACTOSE INTOLERANCE
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Formal testing for lactose intolerance is valuable.
Elimination diet
Probably the most common way that people self-diagnose lactose intolerance is by an elimination diet, a diet that eliminates obvious milk and milk products. There are several problems with this type of "testing."
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Milk products are so common in prepared foods that it is likely that an elimination diet that is not rigorous (i.e., does not eliminate all milk) will still include substantial amounts of milk. Thus, persons with severe lactase deficiency attempting an elimination diet may be ingesting enough lactose to have symptoms and erroneously conclude that lactose intolerance is not responsible for the symptoms.
- People often make the assumption that they are lactose intolerant based on a short trial of elimination. A short trial may be adequate if symptoms are severe and occurring daily, but not if the symptoms are subtle and/or variable. In the latter case, an elimination diet may need to be continued for weeks.
- Because symptoms of lactose intolerance are subjective and variable, there always is the possibility of a "placebo effect" in which people think they feel better eliminating milk when, in fact, they are no better. With subjective symptoms such as those of lactose intolerance, a placebo effect can be expected to occur 20%-40% of the time
If an elimination diet is to be used for diagnosing lactose intolerance, it should be a rigorous diet. The diet also needs to be continued long enough to clearly evaluate whether or not symptoms are better. Elimination of all milk products should eliminate symptoms completely if lactose intolerance alone is the cause of the symptoms.
Milk challenge
A milk challenge is a simpler way of diagnosing lactose intolerance than an elimination diet. A person fasts overnight and then drinks a glass of milk in the morning. Nothing further is eaten or drunk for 3-5 hours. If a person is lactose intolerant, the milk should produce symptoms within several hours of ingestion. If there are no symptoms, it is unlikely that lactose intolerance is the cause of the symptoms. It is important for the milk that is used to be non-fat milk to eliminate the possibility that fat in the milk is the cause of symptoms and usually occurs in infants and young children.
An important issue in the milk challenge is the amount of milk to use.
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If a person drinks glasses of milk or ingests larger amounts of milk-containing products in their normal diet, then a larger amount of milk (one or two large glasses of milk) should be used in the challenge,
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If the person being tested usually does not drink glasses of milk or ingest larger quantities of milk-containing products, there may be a problem. These larger quantities of milk used for testing may cause symptoms, but the smaller amounts of milk or milk products that these persons ingest in their normal diet may not be enough to cause symptoms.
Breath test
The hydrogen breath test is the most convenient and reliable test for lactase deficiency and lactose intolerance. For the breath test, pure lactose, usually 25 grams (the equivalent of 16 oz of milk), is ingested with water after an overnight fast. In persons who are lactose intolerant, the lactose that is not digested and absorbed in the small intestine reaches the colon where the bacteria split the lactose into glucose and galactose and produce hydrogen (and/or methane) gas. Small amounts of the hydrogen and methane are absorbed from the colon into the blood and then travel to the lungs where they are excreted in the breath. Samples of breath are collected every 10 or 15 minutes for 3-5 hours after ingestion of the lactose, and the samples then are analyzed for hydrogen and/or methane. If hydrogen and/or methane is found in the breath, it means that the small intestine of the person having the test was unable to digest and absorb all of the lactose. He or she is lactase deficient.
Blood glucose test
The blood glucose test is an older test for lactase deficiency and lactose intolerance. For the blood glucose test, lactose is ingested (usually 0.75 to 1.5 gm of lactose per kg of body weight) after an overnight fast, and serial blood samples are drawn and analyzed for glucose. If the level of blood glucose rises more than 25 mg/100ml, it means that the lactose has been split in the intestine and the resulting glucose has been absorbed into the blood. This implies that lactase levels are normal.
Stool acidity test
The stool acidity test is a test for lactase deficiency in infants and young children. For the stool acidity test, the infant or child is given a small amount of lactose orally. Several consecutive stool samples then are tested for acidity. With a deficiency of lactase, unabsorbed lactose enters the colon and is split into glucose and galactose. Some of the glucose and galactose is broken down by the bacteria into acids, for example, lactic acid. Lactic acid turns the stool acidic. Therefore, a lactase deficient infant or child will develop an acidic stool following the test dose of lactose.
Intestinal biopsy
The most direct test for lactase deficiency is biopsy of the intestinal lining with measurement of lactase levels in the lining. The biopsy can be obtained by endoscopy or by special capsules that are passed through the mouth or nose and into the small intestine.
Sources of lactose in the diet
Although milk and foods made from milk are the only natural sources of lactose, lactose often is "hidden" in prepared foods to which it has been added. People with very low tolerance for lactose should know about the many food products that may contain lactose, even in small amounts. Food products that may contain lactose include:
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Bread and other baked goods
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Processed breakfast cereals
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Instant potatoes, soups, breakfast drinks
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Margarine
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Lunch meats
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Salad dressings
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Candies and other snacks
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Mixes for pancakes, biscuits, and cookies.
4. TREATMENT OF LACTOSE INTOLERANCE
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Dietary changes
The most obvious means of treating lactose intolerance is by reducing the amount of lactose in the diet. Fortunately, most people who are lactose intolerant can tolerate small or even moderate amounts of lactose.
It often takes only elimination of the major milk-containing products to obtain sufficient relief from their symptoms. Thus, it may be necessary to eliminate only milk, yoghurt, cottage cheese, and ice cream. Though yoghurt contains large amounts of lactose, it often is well-tolerated by lactose intolerant people. This may be so because the bacteria used to make yoghurt contain lactase, and the lactase is able to split the lactose during storage of the yoghurt as well as after the yoghurt is eaten (in the stomach and intestine).
Substitutes for milk also are available, including soy and rice milk.
For individuals who are intolerant to even small amounts of lactose, the dietary restrictions become more severe.
Lactase enzyme
Tablets of lactase are available to take with milk-containing foods.
Adaptation
Some people find that by slowly increasing the amount of milk or milk-containing products in their diets they are able to tolerate larger amounts of lactose without developing symptoms.
Calcium and vitamin D supplements
Milk and milk-containing products are the best sources of dietary calcium, so it is no wonder that calcium deficiency is common among lactose intolerant persons. This increases the risk and severity of osteoporosis and the resulting bone fractures. It is important, therefore, for lactose intolerant persons to supplement their diets with calcium. A deficiency of vitamin D also causes disease of the bones and fractures. Milk is fortified with vitamin D and is a major source of vitamin D for many people. Although other sources of vitamin D can substitute for milk, it is a good idea for lactose-intolerant persons to take supplemental vitamin D to prevent vitamin D.
Source :
http://www.medicinenet.com/food_allergy/page3.html
http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/
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