SUMMARY
Milk and other dairy foods are important sources of several essential nutrients. Some individuals, however, may experience gastrointestinal symptoms following the consumption of these foods. These adult lactose maldigesters have low levels of the intestinal enzyme lactase. Lactase is necessary to digest lactose, the main carbohydrate in milk and dairy products. Whenever the quantity of lactose ingested exceeds the capacity of intestinal lactase to digest it, lactose maldigestion symptoms such as abdominal bloating, stomach cramps and diarrhea may result.
A diagnosis of lactose maldigestion most often is based on breath hydrogen levels following intake of an unusually large amount of lactose in water (50 g of lactose). This test tends to exaggerate the prevalence of lactose maldigestion, since the majority of lactose maldigesters (diagnosed by this method) can still tolerate standard serving sizes of milk and other dairy foods (one glass of milk contains 12 g of lactose) without experiencing adverse symptoms.
Tolerance can be improved by making appropriate choices in the amount and types of dairy foods consumed. Milk should be consumed in smaller quantities more often throughout the day, and preferably with a meal. Also, yogurt, because of the lactase activity of yogurt cultures, and many aged cheeses, because of their low lactose content, are well tolerated. Eating small amounts of dairy products each day to “adapt” the colonic bacteria may possibly eliminate or reduce symptoms of lactose maldigestion.
Lactose maldigestion should not be confused with milk allergy, which is much less common, and occurs most often in infants. Its occurrence in older children and adults is less frequent. Since milk allergy is difficult to diagnose, milk and dairy products are usually eliminated from the diet for two weeks to see if the symptoms disappear. If individuals can tolerate yogurt and cheese without any symptoms, cow’s milk allergy is unlikely to be the cause of the problem. Milk should be reintroduced in small amounts and at regular intervals to see if the allergy has been outgrown.
Because milk and dairy products are an important source of high quality protein, vitamin D, calcium and other essential nutrients, these foods should not be eliminated from the diet, unless absolutely necessary.
Lactose Maldigestion... A misconception?
There are many questions and misconceptions about lactose maldigestion. Many people believe that “lactose intolerant” individuals cannot drink milk or eat dairy products. Some commonly asked questions include:
- Should lactose maldigesters actually avoid all milk and dairy products?
- Can these individuals eventually “adapt” to enjoy these foods?
- What are the potential benefits of yogurt?
- What is the difference between lactose maldigestion and milk allergy?
These questions are addressed below. Milk and other dairy foods are an important source of high quality protein, vitamin D, calcium and other essential vitamins and minerals (8). Some individuals, however, may experience gastrointestinal symptoms following the consumption of these foods. Bloating, gas and diarrhea are common complaints from people of Asian, Middle Eastern, aboriginal North American, African and Latin American descent. These symptoms result from lactose maldigestion and cause “lactose intolerant” people to avoid milk and dairy products.
Extensive population studies in the late 1960’s and early 1970’s showed that much of the world’s adult population (approximately 70%) have low levels of the intestinal enzyme lactase. Lactase is necessary to digest lactose, the main carbohydrate in milk and dairy products. The activity of lactase reaches a maximum immediately after birth and then decreases in the majority of people after weaning (22), usually between the age of 3 to 5 years (21). Whenever the quantity of lactose consumed exceeds the capacity of the intestinal lactase to digest it, the undigested lactose passes into the large intestine. There it is fermented by colonic flora. The fermentation products result in gastrointestinal symptoms of lactose maldigestion (21).
Approximately 30% of adults, mostly Northern and Western Europeans, have adapted to maintain high lactase activity into adulthood. Research concludes that this adaptation is genetically controlled, permanent, and is related to a long tradition of consuming milk and dairy products in these regions of the world (21).
Significance of a lactose tolerance test
To determine if lactose maldigestion is present, a single large dose of 50 g lactose in water is given to fasting adults. This is equivalent to the amount of lactose in four glasses of milk. (One glass of milk contains about 12 g lactose.) The extent to which this lactose load is digested in the small intestine is determined indirectly by measuring breath hydrogen and/or blood glucose levels (21).
Unfortunately, the extensive symptoms resulting from this unusually large lactose load have developed and reinforced the misconception that any lactose load, hence all dairy foods, will cause symptoms. However, in usual situations, the quantity of lactose ingested at any time is much less than in the lactose tolerance test (LTT).
Lactose maldigesters retain some lactase activity which allows for the digestion of small amounts of lactose (20). Scrimshaw and Murray (21) reviewed research findings and concluded the majority of lactose maldigesters can still tolerate standard serving sizes of milk and other dairy products without experiencing adverse symptoms. Only 20 - 30% of maldigesters (or about 1 billion people worldwide) will develop symptoms after consuming one glass of milk (Figure 1).
Increasing the dose of lactose to the amount found in two glasses of milk increases the incidence of symptoms close to 50%. When further increasing the amount of lactose to 50 g (as is used in the lactose tolerance test), almost all maldigesters experienced symptoms (20).
Should lactose maldigesters actually avoid all milk and dairy products?
Although lactose maldigestion is prevalent among some populations, total elimination of dairy foods is unnecessary. The ability to tolerate lactose is not an “all or none” phenomenon. The majority of lactose maldigesters can consume a moderate amount of lactose at one time without experiencing symptoms (Figure 1), considering the following factors:
Quantity
Individuals who experience symptoms after consuming less than one glass of milk should consume smaller servings of milk more frequently. Lactose maldigesters need to determine their individual threshold for occurrence of symptoms and adjust their lactose intake accordingly (20).
Stomach emptying time
Lactase is active in the duodenum (first part of the small intestine) and the ability to handle lactose loads is very closely related to the amount of lactose emptying from the stomach. Drinking milk with other food rather than alone delays stomach emptying time and thus allows the remaining active lactase more time to digest lactose.The severity of symptoms decreases when lactose is consumed as part of a meal (14) (Figure 1).
Drinking milk at room temperature or warmer slows down the stomach emptying time and may be better tolerated than cold milk (20).
Due to its higher fat content, whole milk empties from the stomach more slowly than low fat milk and thus is better tolerated. Also, chocolate milk may be preferable to unflavoured milk because its higher osmolality delays stomach emptying (11, 21) (Figure 1).
Type of dairy food
In addition to the quantity of lactose, the type of dairy food consumed also influences symptoms of lactose maldigestion (21). Most firm cheeses (e.g. cheddar, swiss, mozzarella) contain Iittle, if any, lactose. During the manufacturing of cheese, most of the lactose is removed with the whey. Furthermore, during the aging process of cheese, any remaining lactose is converted to lactic acid and other products (21).
What are the potential benefits of yogurt?
Several researchers (4, 10, 12, 17) have reported a significant improvement in lactose digestion and a virtual elimina- tion of maldigestion symptoms when yogurt is the source of lactose. Although yogurt may contain more lactose than milk (depending on the addition of milk solids to improve texture and viscosity), the lack of maldigestion symptoms is believed to be due to the lactase activity of the bacteria in the yogurt cultures (12).
Since pasteurization destroys lactase activity, only yogurt containing a live bacterial culture appears to be well tolerated by lactose maldigesters (19). This means the culture has to be added after pasteurization, which is the case for all yogurt made in B.C. (2). Lactase is also sensitive to freezing. Frozen yogurts, as currently manufactured, may have little enzyme activity (2, 13) and therefore are less likely to improve digestion.
It may be particularly important to improve lactose digestion in the elderly, since lactase activity declines with age. The results of a Spanish study (24) indicated that lactose digestion in the elderly improved considerably with yogurt.
Why (not) pop a pill?
Commercially available lactase in tablet or liquid form is another means to improve lactose digestion (3, 21). The liquid enzyme is added to milk and it hydrolyzes 70% of the milk sugar within 24 hours.This lactose-reduced milk has been shown to be almost as effective as yogurt in reducing symptoms of lactose intolerance (see Dairy Dictionary: Lactaid). Although these lactose- reduced products are beneficial for lactose maldigesters, they are generally unnecessary if milk is consumed in moderate amounts, and combined with other foods (21).
Can lactose maldigesters eventually “adapt” to enjoy milk or dairy foods?
It has been frequently observed that in lactose intolerant people the symptoms of lactose maldigestion disappear after prolonged periods of lactose intake (7, 16, 18). Gilat et al. (5) reported on lactose maldigesters who consumed gradually increasing amounts of milk (up to 1 L/day) for one year as part of their usual diet. Some had symptoms initially but all came to tolerate the milk without complaints. There was no increase in lactase activity, however, it has been suggested that prolonged consumption of lactose may favour colonic bacteria which don’t result in symptoms (1,9).
Thus, although the mechanism for this “colonic adaptation” to lactose has not been clearly demonstrated (1, 9), symptoms may be eliminated or reduced by eating small amounts of dairy foods each day (20, 21).
Effect on utilization of other nutrients
In terms of other nutrients, low lactase activity has little, if any, effect on the absorption of protein, fat, vitamins or minerals from milk (21).
Some evidence suggests that osteoporosis is more common in lactose maldigesters (21). Whether this is due to the avoidance of calcium-containing milk and dairy products or is a result of impaired calcium absorption has been questioned. A recent study showed that dietary calcium absorption is not impaired in lactose maldigesters and that they may actually absorb the calcium from milk better than lactose digesters (6). Furthermore, in a study of 342 white women (23), lactose digesters and lactose maldigesters had similar calcium intakes and bone density. It was concluded that lactose maldigestion in white women is not a risk factor for low bone mass.
References on Lactose Maldigestion:
(1) Arrigoni E., P. Pochart, B. Flourie, P. Marteau, C. Franchisseur, J.C. Rambaud.1992. Does a prolonged lactose ingestion induce clinical and colonic metabolism adaptations in lactose intolerant subjects? Gastroenterology 102:A197.
(2) Astro Dairy Products, Dairyland Foods, Foremost Foods, Island Farms, Lucerne Foods, Olympic Dairy Products. 1994. Personal communication.
(3) Dairy Council Digest.1989. Food sensitivity and dairy products.60:25 - 30.
(4) Devit O., P. Pochart, J.F. Desjeux.1988. Breath hydrogen concentration and plasma glucose, insulin and free fatty acid levels after lactose, milk, fresh or heated yogourt ingestion by healthy young adults with or without lactose malabsorption. Nutr.4:131 - 135.
(5) Gilat T., S. Russo, E. Gelman-Malachi, T.A.M. Aldor.1972. Lactase in man: a nonadaptable enzyme.Gastroenterology 62:1125 - 1127.
(6) Griessen M., B. Cochet, F. Infante, A. Jung, P. Bartholdi, A. Donath, E. Loizeau, B.Courvoisier.1989. Calcium absorption from milk in lastase-deficient subjects. Am. J. Clin. Nutr.49:377 - 384.
(7) Habte D., G. Sterky, B. Hjalmarsson.1973. Lactose malabsorption in Ethiopian children. Acta Paediatr. Scand.62:649 - 654.
(8) Health and Welfare Canada. 2008. Nutrient value of some common foods. Ottawa: Minister of Health.
(9) Hertzler S., D A. Savaiano.1993. Colonic metabolism and lactose tolerance. FASEB J.7: A583.
(10) Kolars J.C., M.D. Levitt, M. Ajouji, D.A. Savaiano. 1984. Yogurt - an autodigesting source of lastose. New Engl.J.Med. 310:1 - 3.
(11) Lee C.M., C.M. Hardy.1989. Cocoa feeding and human lactose intolerance. Am. J. Clin. Nutr. 49:840 - 844.
(12) McDonough F.E., A.D. Hitchins, N.P. Wong, P. Wells, C.E. Bodwell. 1987. Modification of sweet acidophilus milk to improve utilization by lactose-intolerant persons. Am. J. Clin. Nutr. 45: 570 - 574.
(13) Martini M.C., D.E. Smith, D A. Savaiano.1987. Lactose digestion from flavored and frozen yogurts, ice milk, and ice cream by lactase deficient persons. Am.J.Clin.Nutr.46:636–640.
(14) Martini M.C., D.A. Savaiano.1988. Reduced intolerance symptoms from lactose consumed during a meal. Am.J.Clin.Nutr. 47:57-60.
(15) Martini M.C., D. Kukielka, D A. Savaiano.1991. Lactose digestion from yogurt: influence of a meal and additional lactose. Am. J. Clin. Nutr. 53:1253 - 1258.
(16) Montgomery R.K., H A. Bueller, E.H.H.M. Rings, RJ. Grand.1991. Lactose intolerance and the genetic regulation of intestinal lactase- phlorizin hydrolase. FASEB J.5:2824-2832.
(17) Murao K., K. Igaki, H. Hasebe, T. Kaneko, H.Suzuki.1992. Differences in breath hydrogen excretion and abdominal symptoms after ingestion of milk and yogurt by lactose intolerant individuals. J. Jap. Society of Nutr. & Food Sc. 45:507 - 512.
(18) Reddy V.,J. Pershad.1972. Lactase deficiency in Indians. Am.J.Clin. Nutr. 25:114 - 119.
(19) Savaiano D.A., A. Abou El Anouar, D.E. Smith, M.D. Levitt.1984. Lactose malabsorption from yogurt, pasteurized yogurt, sweet acidophilus milk, and cultured milk in lactase-deficient individuals. Am.J.Clin.Nutr. 40:1219 - 1223.
(20) Savaiano D. A.1994. Lactose intolerance:dietary management. In: Dairy Products in Human Health and Nutrition. M. Serrano Rios, A. Sastre, M.A. Perez Juez, A. Estrala, C. de Sebastian (eds.). Rotterdam, Netherlands: A.A. Balkema. pp.401 - 405.
(21) Scrimshaw N.S., E.B. Murray.1988. The acceptability of milk and milk products in populations with a high prevalence of lactose intolerance. Am. J. Clin. Nutr.48 (suppl.): 1083 - 1159.
(22) Solomons N.W.1986. An update on lactose intolerance. Nutr. News 49(1):1 - 3.
(23) Slemenda C.W., J.C. Christian, S. Hui, J. Fitzgerald,C.C.Johnston Jr.1991. No evidence for an effect of lactase deficiency on bone mass in pre- or post-menopausal women. J. Bone & Mineral Res.6:1367 - 1371.
(24) Varela-Moreiras G., J.M. Antoine, B. Ruiz-Roso, G. Varela. 1992. Effects of yogurt and fermented-then-pasteurized milk on lactose absorption in an institutionalized elderly group. J.Am. College Nutr.11:168 - 171.
Milk Allergy
Lactose maldigestion should not be confused with milk allergy which is much less common. Milk allergy is a sensitivity to the protein in milk, not lactose (a carbohydrate), and occurs most often in infants. Sensitivity to cow’s milk protein is higher in early years because of the immaturity of the digestive and immune systems. An estimated 0.3% to 7.5% of infants (2, 3) experience cow’s milk allergy. The incidence is higher in infants who are fed cow’s milk very early in life (i.e. before 3 - 4 months of age) and/or who have a family history of allergies (2, 3). It usually disappears by 2 years of age but in a few cases may continue or appear later in life. By the age of five, 80% of children outgrow milk allergies (1).
The most common symptoms of milk allergy involve the gastrointestinal tract (i.e. abdominal pain, vomiting, diarrhea), respiratory tract (i.e. nasal congestion), and skin (i.e. rash). The onset of symptoms varies from 45 minutes to more than 20 hours after consuming milk (4).
The diagnosis of milk allergy is difficult because of the wide spectrum of clinical symptoms (2, 3). The generally accepted procedure to identify milk allergy is to remove cow’s milk from the individual’s diet for 7 to 14 days to see if the symptoms disappear. If symptoms persist, cow’s milk is unlikely to be the cause of the problem.
On the other hand, if symptoms disappear, it is recommended to eliminate milk from the diet for about 1 to 3 months and then reintroduce it in small amounts and at regular intervals to determine whether the allergy has been outgrown (5). Generally, if a family history of allergies exists, cow’s milk should not be introduced to the child before one year of age.
Lactose maldigesters can usually tolerate cheese and yogourt without experiencing adverse symptoms, but individuals who are allergic to the protein in milk cannot tolerate any dairy foods.
Prolonged exclusive breastfeeding (up to 6 months) is recommended to prevent or delay allergic symptoms in susceptible infants (3). Furthermore, the newborn baby should not be exposed to formula in the hospital nursery, since this first exposure, although symptom free, might act as a sensitizing dose. Subsequent exposures to milk may be associated with symptoms (5).
Because cow’s milk and dairy products are important sources of many essential nutrients, these foods should be introduced in the infant’s diet according to recommendations, and not be eliminated from the diet, unless absolutely necessary.
References on Milk Allergy:
(1) Bock S.A.1988. Food Allergy. A Primer for People. 2nd ed. New York: Vantage Press.
(2) Dairy Council Digest. 1989. Food sensitivity and dairy products. 60:25 - 30.
(3) Fousard T. 1985. Development of food allergies with special reference to cow’s milk allergy. Pediatrics 75 (suppl.): 177 - 180.
(4) Hill D.J., R.P.K. Ford, M.J. Shelton, C.S. Hosking.1984. A study of 100 infants and young children with cow’s milk allergy. Clin.Rev. Allergy 2:125 - 142.
5) Joneja J.1994. Pediatric nutrition allergies. Presentation in Vancouver.
© BC Dairy Foundation 2008
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