An intolerance to disaccharides (two sugars (saccharides) bound together), of which the best known is lactose intolerance, is caused by an impairment to the breakdown and absorption of certain sugars.
What should happen is that complex carbohydrates (polysaccharides and oligosaccharides) are broken down by enzymes in the digestive tract into disaccharides. The disaccharides are then split into their two monosaccharide (single sugar) components by special disaccharidase enzymes in the cells lining the small intestine. The monosaccharides are then absorbed through the gut wall, into blood. Monosaccharide sugars are normally efficiently absorbed in the small intestine.
However, if there is a deficiency in the production of the enzymes, the disaccharides remain undigested and move into the large bowel intact where they are fermented by the resident microorganisms – resulting in the common symptoms of gas production causing abdominal bloating, pressure, pain, wind and diarrhoea.
The carbohydrate content of the normal western diet is about 60% starch, 30% sucrose, and 10% lactose, and each of those is digested differently.1
Lactose is the sugar in milk. It occurs in the whey (liquid) part of milk. Foods made from milk will contain specific quantities of lactose, depending on the amount of whey in their composition, Hard cheeses are mainly casein; the whey (liquid) is removed in their manufacture. Most contain negligible amounts of lactose and are tolerated by most lactose-intolerant individuals. Soft cheeses contain a higher percentage of whey, and consequently, a higher level of lactose and may not be tolerated by the lactase deficient person
Lactase, the enzyme that breaks down lactose, splits the lactose into two monosaccharides or single sugars: glucose and galactose. Someone who produces very little lactase cannot break down large quantities of lactose. So the undigested lactose moves into the colon, where it provides an excellent base for microbial fermentation.
Lactose intolerance is quite different from milk allergy, in which a person’s immune system reacts to the protein in milk.
Table sugar (white sugar, demarara sugar, brown sugar, icing sugart, etc.) and syrups are examples of sucrose. Sucrose is usually derived from sugar beet or sugar cane but is also found in many fruits and some grains and vegetables. The enzyme that breaks down sucrose, sucrose alpha-glucosidase, or sucrase, splits sucrose into the two monosaccharides or single sugars: glucose and fructose.
These make their way through the gut wall into the blood stream. A deficiency of sucrase results in inadequate breakdown of sucrose, which moves into the large bowel and provides an excellent substrate for microbial fermentation, resulting in the symptoms described above.
Maltose is the disaccharide which results when the starches in grains and starchy vegetables are digested. The starch, which is composed of long chains of glucose molecules, is gradually split into smaller and smaller chains by amylase enzymes. Finally, the last two joined glucose molecules become maltose. The enzymes maltase and isomaltase then split maltose into individual glucose molecules, which are absorbed through the intestinal wall into circulation. If there is a deficiency in the enzymes that split these linkages, free glucose molecules will not be released and absorbed, and the remaining undigested starch or sugar will be pass into the large bowel where bacteria ferment it.
Symptoms of disaccharide intolerance
Diarrhoea, abdominal distention, pain, and flatulence (wind) are the usual symptoms of disaccharide intolerance.2 , These symptoms are the result of microbial fermention and a change in osmotic pressure in the large bowel.
As excessive amounts of undigested sugars enter the colon, fluid is drawn in to normalise the increased osmotic pressure. Watery diarrhoea or loose stool results from this increase in fluid in the bowel.3 Gases are produced as a result of an increase in microbial growth and fermentation. This results in abdominal bloating, pain, and flatulence (wind). In addition, organic acids are produced by microbial fermentation in the bowel, which tend to increase motility in the digestive tract. The increase in speed with which food passes through the digestive tract results in inadequate enzymatic breakdown (digestion) of the food, thus increasing the amount of substrate available for microbial fermentation in the large bowel. Consequently, maldigested disaccharides lead to symptoms in a cyclical pattern:4 The initial diarrhoea caused by fermentation in the colon leads to speeding up of intestinal transit of food. As contact with intestinal enzymes is reduced because of inadequate churning and mixing, more undigested starches and sugars move into the colon. This increases the amount of fermentation products in the colon, which perpetuates the cycle. Once it starts, removal of all maldigested carbohydrate is needed to interrupt the cycle and allow the system to return to normal.
In most cases, a disaccharide intolerance is dose-related. Usually the intestinal cells are producing a limited amount of enzyme, so that small doses of disaccharides in foods can be processed. Problems occur when the amount of disaccharide in the food exceeds the capacity of the enzymes to digest it. The important thing is to determine a person’s capacity to handle the sugar. As long as the amount consumed remains within an individual’s limits, they should remain symptom free.
Conditions that may trigger a disaccharide intolerance
Intolerance may occur as a result of any condition that causes a decrease in disaccharide enzyme activity:5
• Inherited (congenital) enzyme deficiency, which is a rare condition that is present from birth
Inherited (Congenital) Disaccharidase Deficiencies
Congenital Lactase Deficiency
Congenital Sucrase-Isomaltase Deficiency
The prevalence of congenital sucrase-isomaltase deficiency is estimated to be 1 in 5,000 people of European descent. This condition is much more prevalent in the native populations of Greenland,10 Alaska, and Canada, where as many as 1 in 20 people may be affected. This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of a child with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Primary and Secondary Disaccharidase Deficiency
If the deficiency is a result of an inherited tendency, it is likely that the intolerance will be lifelong. This is called a primary deficiency. The foods that cause the problem must always be avoided. In the case of lactose intolerance there are two types of primary deficiency: Congenital (discussed above) and adult onset lactose intolerance. In adult onset lastose intolerance, lactase enzyme production starts to decrease as a person matures. After childhood, 80% of the adult population of the world starts to experience varying degrees of lactose intolerance. In some cases, the deficient enzyme can be provided as medication to be consumed with the food or as drops to be added to foods (e.g., lactase in the form of Lactaid or Lacteeze). The treated food usually will be tolerated.
If the enzyme deficiency is a result of damage to the intestinal cells, caused by infection, food allergy, food protein enteropathy, or strong drugs, it is called a secondary deficiency and is usually temporary. When the cause is removed, the cells will start to heal and gradually resume production of the enzymes. Over time, foods to which an affected individual was intolerant will be processed adequately and tolerated.
Identifying the disaccharide enzyme that is deficient
The most definitive method of diagnosing deficiency in any of disaccharide enzymes is by measuring the activity of the enzyme in the epithelial cells of the small intestine.11 This technique involves taking an endoscopic biopsy of the epithelium and homogenizing the tissue. A sample of the homogenate is then mixed with each of the substrates: sucrose, lactose, and maltose. The activity of the enzyme is then calculated by measuring the amount of glucose released from each substrate, since all of the disaccharides contain glucose which is released by the action of the enzyme on the disaccharide.
Because the test is invasive, many people prefer to try to control the symptoms by dietary methods. If the deficiency is due to a temporary deficiency, dietary exclusion of all the disaccharides, followed by reintroducing each one individually in increasing doses, may be feasible.
In general, if an individual is consuming a wide range of the allowed foods and the condition is a secondary (temporary) deficiency, nutritional supplements should not be necessary. The amount of supplement that may be required will depend on individual tolerances to the disaccharide-containing food; some people will be able to tolerate a small amount of the food and so any deficiencies will be minimal.
Feeding the lactose intolerant baby
A breastfed baby will ingest significant quantities of lactose in the mother’s milk. The lactose composition of her milk will remain constant, regardless of whether she consumes milk and dairy products. Human milk contains 6% (weight in volume) lactose compared to 4% in cow’s milk. Human milk does not contain sucrose, maltose, or starch, so intolerance of other disaccharides is not a problem for the baby during breastfeeding.
If the baby’s lactose intolerance is secondary, as a result of a gastrointestinal tract infection or other transient condition, most specialists advise continuing breastfeeding and as the diarrhoea will gradually diminish as the underlying inflammation disappears.
Alternatively, the mother can pump her breastmilk and treat the milk with lactase drops (4 drops per 250 mL milk), and allow the enzyme to act for 24 hours in the fridge. The baby will be fed the lactose-free milk the next day. This is continued until the diarrhoea stops, when the baby can be gradually put back to the breast.
• Infant formulas that are lactose free and sucrose free can be given to a disaccharidase-deficient infant.
• If the baby is not allergic to milk, a milk-based formula that is free from lactose and sucrose is suitable.
• If the infant is allergic to cow’s milk proteins an extensively hydrolyzed sucrose-free casein formula such as Enfamil Nutramigen (Mead Johnson) and Enfamil Pregestimil (Mead-Johnson) is recommended..
The Disaccharide-restricted diet
A convenient way to manage disaccharide intolerances is to conduct the diet in three phases:3
A serving size or more of each of the relevant food types (see below) should be consumed. Development of symptoms (particularly diarrhoea) over the following 24 hours should indicate the culprit disaccharide
• Lactose tolerance is determined by consuming complete milk and dairy products containing complete milk.
3. Lloyd-Still JD, Listernick R, Buentello G. Complex carbohydrate intolerance: diagnostic
4. Joneja JMV. Maldigestion of carbohydrates. In: Joneja JMV. Digestion, Diet and Disease.
5. Perman JA. Carbohydrate malabsorption. In: Lifshitz F, ed. Nutrition for Special Needs
6. Torniainen S, Savilahti E, Järvelä I. Congenital lactase deficiency—a more common dis-
7. Savilahti E, Launiala K, Kuitunen P. Congenital lactase deficiency: a clinical study on 16
8. Jarvela I, Enattah NS, Kokkonen J, Varilo T, Savilahti E, Peltonen L. Assignment of the
9. Belmont JW, Reid B, Taylor W, et al. Congenital sucrase-isomaltase deficiency presenting
10. Gudmand-Hoyer E, Fenger HJ, Kern-Hansen P, Madsen PR. Sucrase deficiency in Green-
11. Lu J, Grenache DG. High-throughput tissue homogenization method and tissue-based
First published in September 2013
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