Disaccharide intolerance

A number of other intolerances or allergic reactions to foods can also lead to similar persistent diarrhoea, loss of intestinal mucosa and hence malnutrition. The problem of disaccharide intolerance was discussed in section 4.2.2.2. In general, once the offending food has been identified, the patient s condition has stabilized and body weight has been restored, continuing treatment is relatively easy, although avoidance of some common foods may provide significant problems. 

Lactose, the milk sugar, is a reducing disaccharide consisting of glucose and galactose moieties. The estimated annual worldwide availability of lactose as a byproduct from cheese manufacture is several million tons [1,2], but only about 400 000 t/a lactose is processed further from cheese whey [3], Non-processed whey is an environmental problem due to its high biochemical and chemical oxygen demand [2], The use of lactose as such is limited by two main factors relatively low solubility of lactose in most solvents and lactose intolerance in human body [1]. 

The disaccharide lactose, is only found in milk and is hydrolysed with water in the presence of an enzyme lactase to form the monosaccharide glucose and galactose. This occurs in the small intestine. Some people, and particularly those from Eastern and African countries, are deficient in lactase so they are intolerant of milk. This can cause diarrhoea. Many African and Chinese foods do not include milk for this reason. 

Lactose, the major sugar found in milk, is a disaccharide reducing sugar, but unlike the other sugars it is not particularly soluble. Some individuals are unable to metabolise lactose and are therefore described as lactose intolerant. This is because they lack the enzyme lactase which is needed for lactose metabolism. Lactose intolerance is common in those parts of the world where humans do not consume any dairy products after weaning. In practice this means Asia, so it is possible that the majority of the world s population is lactose intolerant. 

Lactose, the primary sugar found in milk, is a disaccharide composed of glucose and galactose. With age, many children lose their ability to digest large amounts of lactose, leading to lactose intolerance. This permanent condition, which occurs in adolescence and adulthood, is not an important health concern, although it may lead to an aversion to milk, an important food. 

Lactulose is a disaccharide of galactose and fructose and includes some lactose, so cannot be used by patients with galactose or lactose intolerance and must be used with caution in diabetes. 

The answer is b. (Murray, pp 190—198. Scriver, pp 1521-1552. Sack, pp 121-138. Wilson, pp 287-317.) In many populations, a majority of adults are deficient in lactase and hence intolerant to the lactose in milk. In all populations, at least some adults have lactase deficiency (223000). Since virtually all children are able to digest lactose, this deficiency obviously develops in adulthood. In lactase-deficient adults, lactose accumulates in the small intestine because no transports exist for the disaccharide. An outflow of water into the gut owing to the osmotic effect of the milk sugar causes the clinical symptoms. Steatorrhea, or fatty stools, is caused by unabsorbed fat, which can occur following a fatty meal in persons with a deficiency of... 

The intestinal juice also contains enzymes to break down individual disaccharides. The one to break down lactose is very active in babies, as might be expected, but less so in adults. Its low activity in many Oriental people is responsible for lactose intolerance - milk products cause problems. 

Sucrase (also called saccharase and invertase) hydrolyzes sucrose. In contrast to the abundant information available on the yeast invertase, little is known of the mammalian sucrases. The significance of invertase and lactase in absorption is illustrated by inborn errors of metabolism in which these two enzymes are absent in the intestinal secretion. (The fact that lactase deficiency does not interfere with growth indicates that the galactose needed for biosynthesis of brain lipids or lens proteins can be synthesized endogenously in amounts sufficient to fulfill the metabolic requirements.) In that case, there is an intolerance to lactose or sucrose with no increase in blood glucose levels or without an increase in the levels of disaccharides... 

Aspects of chemical methods used in the structural elucidation of polysaccharides and complex carbohydrates have been reviewed. In a critical examination of the use of g.l.c.-m.s. in the identification of TMS ethers of monosaccharides, a standardized method, which uses a medium resolution mass spectrometer and short chromatographic columns, has been proposed. TMS Ethers of monosaccharides have been characterized by g.l.c.-chemical ionization m.s. with ammonia as reagent gas. Molecular weights were determined, and fragment ions were produced in a quantity high enough to differentiate between stereoisomers (epimers and anomers). Disaccharides have been determined by permethylation followed by g.l.c. The method has been used in the detection of carbohydrate intolerance secondary to intestinal disaccharidase deficiency. 

Lactose is found in milk and other dairy products, so it is often called milk sugar. Disaccharides such as lactose need to be cleaved to monosaccharides in order to be absorbed into the bloodstream. The acetal bond in lactose is cleaved by the enzyme lactase. Many adults are lactose intolerant because their bodies don t make lactase. For such individuals, consumed lactose doesn t get absorbed into the bloodstream and the result is abdominal discomfort. 

Figure 22.12 Milk and Lactaid. It is estimated that up to 75% of the world s adult population is lactose (milk sugar) intolerant to some degree. Lactaid contains the enzyme lactase, which catalyzes the reaction of the disaccharide lactose to form the monosaccharides galactose and glucose. 

Adults who are lactose intolerant cannot break down the disaccharide in milk products. To help digest dairy food, a product known as Lactaid can be added to milk and the milk then refrigerated for 24 hours. (16.5,16.6)... 

The disaccharide in milk is lactose, which is broken down by lactase in the intestinal tract to monosaccharides that are a source of energy. Infants and small children produce lactase to break down the lactose in milk. It is rare for an infant to lack the ability to produce lactase. However, the production of lactase decreases as many people age, which causes lactose intolerance. This condition affects approximately 25% of the people in the United States. A deficiency of lactase occurs in adults in many parts of the world, but in the United States it is prevalent among the African American, Hispanic, and Asian populations. 

Contrary to a common belief, lactose intolerance, present in some 70% of the world s population, is not a major obstacle to widespread consumption of dairy products, because the disaccharide is virtually absent in fully ripened cheeses, and it is reduced to much more tolerable levels in yogurt see Suarez, F. L., and D. A. Savaiano. 1997. Diet, genetics, and lactose intolerance. Food Technology 51(3) 74-76. 

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