Lactose Intolerance - an overview | ScienceDirect Topics

DISEASE DESCRIPTION
Lactose intolerance occurs when the ability of the gastrointestinal (GI) tract to digest lactose is impaired. Lactose is a disaccharide sugar found in milk and is produced exclusively by the mammary glands of mammals. The digestion of lactose depends on the small intestinal brush border enzyme lactase-phlorizin hydrolase (lactase). Low levels of lactase enzyme result in indigestion of the lactose sugar. The undigested lactose increases the osmotic force in the bowel lumen and is fermented by the intestinal flora in the colon. The effects of the increased osmotic force and the products of fermentation of lactose together produce the symptoms of lactose intolerance, which are bloating, diarrhea, flatulence, and cramping.
Calcium
Dietary calcium is an important element in skeletal development. Dairy products can account for up to three-quarters of dietary calcium in some populations. Milk is a rich source of calcium. Nevertheless, many minorities in the United States and population groups throughout the world drink decreasing amounts of milk after early childhood and little milk as adults. Given the high prevalence of lactose intolerance, alternatives to cow's milk should be identified for those who cannot tolerate lactose and desire a milk alternative. Lactose-intolerant individuals ultimately attribute their discomfort to lactose-containing foods and voluntarily reduce or eliminate their milk intake. Data from National Studies in the United States indicate African-American and Hispanic women have lower intakes of calcium compared with non Hispanic women. An Institute of Medicine Report concludes that the disparity in calcium intake “may be explained in part by the much higher prevalence of lactose intolerance among African-Americans and Hispanics, sometimes resulting in their subsequent avoidance of milk”. In general, populations at risk for lactose intolerance report a lower calcium intake as a result of the decline in the intake of milk and milk products. One solution to this problem is to educate lactose-intolerant groups as to alternative calcium-containing foods, reinforce appropriate cultural patterns and dietary practices that include alternatives to milk and identify other culturally acceptable calcium-containing foods. Meeting the calcium requirement with an alternative diet is a challenge but nevertheless is required for many in the community. Although milk may serve as a primary source of calcium, appreciable quantities of calcium can be found in nondairy foods (Table 5).
Table 5. Calcium content in milligrams per 100 g portion or as noteda
Canned sardines (3 oz.)
372
Brewer's yeast (2 tbs)
66
Buckwheat pancakes
249
Lobster
65
Kale (raw)
225
Green beans
63
Mustard greens
220
Flounder
61
Muffinsb
206
Bran flakes
61
Wafflesb
192
Canned apricots (1 cup)
57
Figs (dry)
186
Gingerbread (1 piece)
57
Canned salmon (3 oz. with bones)
167
Plain rolls
55
Collard greens
162
Toaster pastry (1 piece)b
54
Oat breakfast cerealb
160
Prunes (dry)
54
Wheat pancakes
158
Orange
54
Almonds
152
Whole egg
54
Tofu (8 oz.)
143
Peanuts
54
Egg yolk
147
Artichokes
51
Corn breadb
139
Cod
50
Kale (frozen)
134
Brussels sprouts
50
Filberts
120
Clams (3 oz.)
47
Beet greens
118
Lima beans
47
Oysters (½ cup)
113
Puffed wheatb
46
Whole cow's milk (100 g)
113
Whole wheat bread (2 slices)
46
Swiss chard
105
Sweet potato
46
Rhubarb (cooked ½ cup)
105
Fruit cocktail (1 cup)
46
Canned shrimp (3 oz.)
98
Raisins (1/2 cup)
45
Okra
92
Apricots
44
Soy beans (1 cup)
90
Farina (1 cup)
44
Sunflower seeds
88
Fig bars (4 cookies)
44
Broccoli
88
Pecans
43
Sauerkraut (1 cup)
85
White bread (2 slices)
42
Potato salad (1 cup)
80
Pecans
43
Peanut butter
74
White bread (2 slices)
42
Spinach
73
Tangerine
40
Dates (dry)
72
Raspberries (raw)
40
Apple sauce
21
a
Oski and Paige modified from Krause and Mahan &amp; Burton.
b
Enriched, fortified, or restored to legal standard when one exists.
Clearly it is more difficult to meet the published calcium recommendation with a diet low in whole cow's milk. A review of the tables of food composition reveals a variety of foods that contain acceptable levels of calcium per 100-g portion or other standard portions. Other lactose-modified dairy products including hard cheeses, yogurts, and lactose-modified milk are good calcium sources.
In addition, lactose digestive aids are available and are increasingly used. The digestive aids commercially available include lactase tablets, lactase preparations, lactose-free milk, and prehydrolyzed milk. Live culture yogurt is another alternative to milk. Lactose in yogurt is better digested than lactose in milk. Tolerance to yogurt is thought to be due to the microbial beta-galactosidase activity that digests the lactose.
General Information
Lactose is the sugar found in milk. Many people, as they grow older, are unable to digest this sugar because they lose the ability to produce the enzyme lactase in the intestinal tract. This enzyme is essential to permit the digestion of lactose and its absorption into the bloodstream. This problem is called lactose intolerance.
When the undigested lactose passes down the intestine into the lower digestive tract, the bacteria normally present in the tract ferments it. This fermentation results in the production of gas and can cause diarrhea.
Many intestinal infections can produce temporary lactase deficiency, but for most people the problem is the permanent reduction in the amount of this enzyme because of aging. The enzyme loss is frequently partial, and the amount remaining varies widely from person to person. Accordingly, the amount of exposure to milk and milk products necessary to produce symptoms varies among individuals.
Conclusion
LI is a perceived barrier for dairy intake. When the LI is due to lactose maldigestion, it is generally managed relatively easily, and thus one of the barriers impeding dietary adequacy is eliminated. Health professionals need to recognize that LI, whether real or perceived, should not be a significant barrier to improving dietary adequacy. They should understand also that LI becomes irrelevant if their patients are unlikely to drink milk, despite the relative ease with which symptoms can often be abated when they do so. Such individuals require special attention from nutrition professionals as it is not a simple task to achieve dietary adequacy without dairy, given contemporary foods and eating patterns. Further studies are required to provide high-quality evidence to support/compare the efficacy of various strategies adopted to treat LI.
Introduction
Lactose malabsorption results from the inability to properly digest lactose, the disaccharide found in mammalian milk. Lactase is an enzyme in the brush border (microvilli) of the small intestine responsible for cleaving lactose into absorbable monosaccharides. Lactase enzyme deficiency leads to lactose malabsorption because the gut is unable to absorb the larger disaccharide. When symptoms such as diarrhea, bloating, flatulence, or abdominal discomfort result from this malabsorption, a diagnosis of lactose intolerance is given. Lactose intolerance affects an estimated 25% to 36% of Americans and 67% to 75% of adults worldwide.1–3 As shown in Table 21.1, the condition occurs in people of all ethnic backgrounds, with a near 100% prevalence observed in Asians. Within the United States, prevalence parallels country of origin, with the highest rates in African Americans, Hispanic Americans, Asian Americans, and Native Americans.4
The generalized nature of abdominal symptoms of lactose intolerance can obscure proper diagnosis,5 resulting in symptom management through medical intervention. However, when properly diagnosed, lactose intolerance may be treated with patient education, lactase supplementation, and dietary modifications,6,7 eliminating the need for medical interventions. In patients experiencing symptoms, a nutritional history and objective measures of lactose malabsorption can lead to the diagnosis of lactose intolerance. Objective measures for lactose malabsorption include stool pH testing, lactose tolerance testing, and hydrogen/methane breath testing. In addition, genomic tests are also available to assess the presence or absence of polymorphisms linked to lactase enzyme deficiency.3
Controversy surrounds the subject of lactose intolerance stemming from the dramatic decrease in dairy consumption that can result from its diagnosis. Numerous studies showed a correlation between decreased dairy consumption and a rise in calcium-dependent conditions, such as osteoporosis, heart disease, and colon cancer.8–13 Studies also indicated that food-based calcium was a better source of this nutrient than supplements. Because dairy foods are the richest and best-absorbed dietary sources of calcium, a careful diagnosis should be made before these foods are eliminated from the patient’s diet. Dietary limitation of calcium-rich foods should be done only in the context of objectively proven lactose intolerance. There is significant variability in the severity of symptoms,14 and many patients with lactose malabsorption are able to consume moderate amounts of lactose without symptoms,15 so both the diagnosis and treatment should be pursued under professional guidance.16
Effects of Lactose on Calcium Absorption
Lactose intolerance has been associated with the development of osteoporosis [40] and, more recently, has been shown to be a predictor of fracture [41]. The connection between lactose intolerance and osteoporosis would appear to be due to a reduced calcium intake associated with an avoidance of milk products [41]. It is therefore appropriate to determine whether milk products cause abdominal symptoms as this may be an indicator of lactose intolerance. Another aspect is that in subjects with lactose intolerance, lactose will itself induce calcium malabsorption from about 25 to 20% [42]. This effect may be due to the osmotic effects of the lactose reducing the effective concentration of calcium within the bowel [36]. Interestingly, in normal subjects, lactose may increase calcium absorption from 22 to 36% [42]. Unfortunately, lactose was not compared to other carbohydrates so it is uncertain as to whether this effect is specific to lactose.
Lactose Intolerance
Lactose intolerance is defined by the occurrence of symptoms after ingestion of lactose, the main carbohydrate in milk. These symptoms may include abdominal pain, bloating, diarrhea, or flatulence. Lactose intolerance is usually secondary to lactose malabsorption caused by a relative deficiency of the disaccharidase lactase, which reduces the ability to digest lactose. Primary lactase deficiency is a condition in which lactase activity falls after weaning around 2 years of age. Secondary lactose intolerance may be temporary and is usually due to mucosal injury associated with a condition or disease such as infectious diarrhea, Crohn's disease, or short bowel syndrome.
In addition to the presence or absence of the lactase enzyme, other factors determine whether a person will have symptoms of lactose malabsorption, including the amount of lactose in the diet, the mixture of lactose with other foods, gastric emptying rate, colonic scavenge of malabsorbed carbohydrate, ethnic origin and age. Although persons of Northern European ancestry commonly maintain the ability to digest lactose into adulthood, primary lactose intolerance is prevalent in African–American, Hispanic, Native American, and Asian populations.
Nutritional management of lactose intolerance consists largely of the removal of lactose from the diet. Lactose is a common ingredient in many foods, including breads, crackers, soups, cereals, cookies, and baked goods. Eliminating or reducing lactose-containing ingredients from one's diet is usually adequate to relieve symptoms. Individuals with primary lactose intolerance may require a permanent dietary change. Individuals with secondary lactose intolerance should eliminate all lactose from their diets for a short period of time ranging from 2 to 6 weeks. If symptoms resolve, lactose may be reintroduced slowly as tolerated by the individual. The amount of lactose that an individual can tolerate is highly variable. Many children can tolerate small amounts of lactose, particularly yogurt or hard cheese, without discomfort. Many adults who consider themselves lactose intolerant can actually tolerate moderate amounts of milk. Lactose intolerant individuals may also tolerate small amounts of lactose consumed over the course of the day better than a large dose all at once.
For individuals who choose to restrict lactose in their diets, a variety of lactose-free and low-lactose food choices are available. Lactose-reduced products, containing 70–100% less lactose than standard foods, are available commercially. Individuals may also choose to consume dairy products with concomitant administration of lactase enzyme tablets or drops.
Frequent consumption of milk and other dairy foods has been associated with better bone health in some studies, and a strict lactose-free diet may not contain adequate amounts of calcium and vitamin D. Table 2 provides a list of some commercially available lactose-free and lactose-reduced calcium supplements.
12.3.4 Lactose Intolerance
Lactose intolerance, also called lactase deficiency, is due to an insufficient level of lactase, which hydrolyzes lactose into glucose and galactose. Therefore, ingestion of milk and dairy products results in bloating, abdominal cramps, diarrhea, and related symptoms. This is a common condition that may develop later in life or may be manifested in early childhood. These individuals can live a normal life by either avoiding milk or dairy products, by consuming lactose-free milk, or by taking a lactase enzyme as supplement. Lactose intolerance is transmitted either in autosomal recessive (Caucasian population) or autosomal dominant (Asian population) fashion.
Lactose Intolerance
Lactose intolerance is an important differential to consider in the diagnosis of food allergy, especially cow's milk allergy. Lactose constitutes a majority of the carbohydrate content of human and cow's milk and is an important part of the energy supply for infants in particular. Lactose is degraded in the gastrointestinal mucosa by the enzyme lactase. Lactose intolerance in the newborn is extremely rare and is caused by congenital deficiency of lactase. Acquired or adult-type lactase deficiency usually appears at the age of 3 to 5 years. Adult-type lactase deficiency is very common in those of African and Asian descent. It is less common in whites, especially in some groups such as the Scandinavian populations; in Denmark, only 3% of adults are affected.
Secondary lactase deficiency is temporary and may occur in response to malnutrition or gastrointestinal infections, which cause temporary damage to the villi of the small intestine, where the enzyme lactase is produced. This sensitivity to lactose often lasts only a few days, followed by complete recovery.
Lactase deficiency (lactose malabsorption) may or may not be associated with gastrointestinal symptoms, depending on many factors and co-existing conditions. Lactose intolerance is defined as a condition with gastrointestinal symptoms after ingestion of lactose in a person with lactase deficiency.38
Lactose intolerance may be diagnosed by oral lactose challenge tests and measurements of increased breath hydrogen, by glucose measurements or by direct enzyme measurements within a duodenal biopsy. A genetic test to diagnose the adult type of lactase deficiency was found to be valid, especially in older children.38,40 Recently, it has been proposed that such tests should be followed by a blinded single-dose challenge of ingested lactose.38
Adult-type or primary lactase deficiency is a lifelong condition. The treatment of lactose intolerance is reduced ingestion of milk and dairy products with lactose. Avoidance does not need to be complete, such as for children with CMPA. A firm diagnosis of lactose intolerance and the threshold for development of symptoms should be established because the sensitivity to lactose is variable. In most lactose-intolerant individuals, considerable amounts of lactose – usually up to 250 mL of milk – may be ingested before symptoms develop. Lactase enzyme replacement is another treatment option.38